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Discussion Starter · #1 ·
I have a problem with my 95 YJ with a 2.5L engine. It runs rich, backfires between shifts, stumbles when accelerating, and has really bad mpg. There are no codes in the computer, the fuel pressure and injectors are ok, the spark is good. I've replaced most sensors, spark plugs, cap and rotor. etc. Please email me at [email protected] with and suggestions, i'll respond to them to inform you if your suggestion helps or not,
Nick Hagen

Nick Hagen
1995 Wrangler
33" Mud Tires and a four banger

Discussion Starter · #2 ·
weren't u going to change some stuff with the computer to give it an extra 20 hp, is that the problem?

1988 Wrangler Laredo 4.2L w/5spd Manual
1995 Wrangler 2.5L w/ 5spd Manual-dixie horn

Discussion Starter · #3 ·
Yes I was going to; however, I never got the chance because I wanted to get it running right before changing anything. It's also not the timing as timing on a 95 is controlled by the PCM (Powertrain Control Module, a fancy name for the computer). Thanks for the help, keep the suggestions coming,
Nick Hagen

Nick Hagen
1995 Wrangler
33" Mud Tires and a four banger

· Registered
13,180 Posts
Here's a starting point...

1. Double check:
a. Fuel pressure.
b. Return line fuel pressure.
Remember the fuel pressure regulator delivers fuel to the injectors, and the surpluss fuel goes back to the tank.
If the return line is kinked, or is clogged, the fuel pressure to the injectors is raised. For a given time that the
injector is open, the higher fuel pressure will cause more fuel to be sent into the cylinder.
c. Injector seating.
d. Look for vacuum leaks, use Carb spray and check for a change in RPM.
e. Remove power from one injector at a time while the engine is running. Do symptoms change equally with removal of each
injector? If so, their all OK, if not, one may be leaking.
f. Have you run some quality fuel injection cleaner (3M, etc.) through the system to insure the pintles are clean and debris free.
g. Spark intensity.
h. Timing.
Distributor advance plates.
g. Timing Chain and distributor gear.
h. Throttle Position Sensor. This may be bad and never throw a code.

2. Remove all spark plugs.
3. BLOW DRY the cylinders with compressed air.
4. Clean and gap the spark plugs.
5. Reinstall the spark plugs.

6. Start the engine.

7. Does the engine IMEDIATLY blow black smoke?
If yes, then the computer is enriching the mix in during Open Loop.
The CTS sensor may be bad.
The computer may be bad.
Use the diagnoistics or voltage readings to determine which.
If no, then the computer and the CTS are working OK during Open Loop.

8. Does the engine blow the black smoke after warm up?
If yes, then the computer only enriches the fuel mix when the fuel system goes into Closed Loop.
This brings other sensors into play, O2, MAP, CTS, Knock, etc. The computer is most likeley OK, and depending on bad sensor input to
enrich the fuel mixture..
If no, then... of course, there must be nothing wrong.

Good Jeepin'


Discussion Starter · #7 ·
Here's what I've done so far, in the order of your suggestions:
1.a. fuel pressure is at 31 psi
b. if you block the return line it spikes to ~70 psi so the return line is ok
c. the injectors are seated ok
d. checked for vaccuum leaks with carb cleaner
e. Yes, all cylinders are equally contributing to engine rpm at idle, there is no leakage.
f. I removed the injectors and had them proffesionally cleaned, injector cleaner is just deisel which p[oured into a 20 gallon gas tank is too diluted to have much effect.
g. The spark intensity is within spec
h. Timing is computer controlled and not adjustable
i. I have 80K on my motor, i probably should check the timing chain
j. The throttle position sensor is new, the old one did die.

2-5. I just installed new spark plugs, gapped correctly.
6-8. The engine never puffs black smoke but according to the Snap-On Scanner, the O2 sensor says itis running rich in closed-loop mode. It has new: MAP sensor, IAC motor (was idling poorly), CTS, I haven't replaced the Knock sensor yet though. Another indication of a rich condidiont is that the cat used to make the floor on the passenger side too hot to touch due to the excess fuel, I removed it because it was starting to melt the insides out of it. It seems to be running rich for no apparent reason, any idea how long the injectors should remain open at idle? mine are at ~5 milliseconds. Everything points to a rich fuel/air mixture but there seems to be no reason for it. Any more advice? I'll check the Timing chain and knock sensor today,
Nick Hagen

Nick Hagen
1995 Wrangler
33" Mud Tires and a four banger

· Registered
1,736 Posts
Doesn't the 4 cyl. have timing gears, not a chain? Perhaps a bad / loose pick-up in the distributor? Got any cracked vacuum lines from age? That could maybe throw the computer off? How long has this been happening? Maybe you got a bad tank of gas, or where you typically get gas got a bad tank(er). You didn't mention fuel filter, or fuel pump flow (not just pressure) been checked?

I'm not a compooter-engine guy, just trying to mention stuff I didn't see mentioned.

Man, you guys sure know your stuff - I'm glad I have a carb though. /wwwthreads_images/icons/smile.gif
Good luck

88YJ, 4"susp, 33"BFGMT, 9k#winch, rear homemade swingout, reb.258, 999, 4.10, weber32/36, GMHEI.

· Registered
6,355 Posts
/wwwthreads_images/icons/wink.gif I sure agree with you about these guys knowing the fuel injection systems, Pete. I'm a fifties kind of guy and was somewhat fearful of the FI on our late-model rides (like our '97 ZJ), but thanks to posts from LEVE and others, I'm beginning to feel more familiar with what is going on up there in front. I feel as if we have the best possible carburetor on our CJ 304 (the 2150), but it will never be the functional equivlent of computerized FI./wwwthreads_images/icons/wink.gif

I never believe any statistics unless my moonguys /wwwthreads_images/icons/crazy.gif/wwwthreads_images/icons/wink.gif made 'em up themselves.

· Official Curmudgeon
5,207 Posts
I did a lot of reading before I put an injected engine in my Jeep. From my understanding in closed loop
mode the O2 sensor takes nearly total control of the fuel. If it thinks it's running rich, it would correct it if
it could.

Some things that would cause this are leaking injector, injector signal wire partially shorted to ground,
(the injector is connected to 12v and the computer supplies the ground to fire it on most models),
injectors firing too often due to engine position sensor errors from distributor (or did I read that yours has
a flywheel sensor).

Lastly, solenoids used in high firing speed applications like dot matrix printers and such have a diode in
the reverse direction to dissipate the current from the coil when power is removed. Otherwise the
solenoid stays energized for a short time after the power is removed. I think I read that injectors have
this diode, but I'm not sure. The ability of a coil to continue current flow after the power is removed is
how your ignition fires the spark plugs.

Sounds like you have been fighting this for a while.


· Registered
6,784 Posts
Here are some things to think about,
**6-8. The engine never puffs black smoke but according to the Snap-On Scanner, the O2 sensor says itis running rich in closed-loop mode. It has new: MAP sensor, IAC motor (was idling poorly), CTS,**

You stand a very good chance on not having the throttle position sensor in the correct position. If your TPS isn't adjusted correctly, your computer may believe the throttle is as much as 20% more open than it actually is.
If the idle air control motor isn't responding, or can't respond enough to compensate, then you will run rich.

Is the computer functioning correctly? How do you know?
**Another indication of a rich condidiont is that the cat used to make the floor on the passenger side too hot to touch due to the excess fuel, I removed it because it was starting to melt the insides out of it.**

There is no way that the oxygen sensor can be functioning correctly if the exhaust temperature got as high as you say it did.
It sounds like you had a plugged converter, and it killed the O2 sensor, and now you are chasing a ghost, O2 complete or partial failure combined with a bad IAC or misadjusted TPS.... (Explains what's happening pretty fast)

Unplug the O2 sensor, and see of that little Strap-On gadget can find the problem...
Does the computer register a trouble code? Is it the correct one for the O2 sensor failure?
Does the computer go into open loop? Does the engine run better in open loop?
(Sometimes it's what doesn't happen that counts, and you must learn to test the test equipment)

(No black smoke, popping back through the intake and over heated exhaust sound like a lean condition to me... What do the spark plugs look like, black and carbon covered, or chalk white?.... Use new plugs to test...)
**I haven't replaced the Knock sensor yet though.**

If your Strap-On toy doesn't say there is a failure, don't worry about this yet. All the Knock sensor does is kick the timing back some.
**It seems to be running rich for no apparent reason,**

This one always gets me. Everything in the Universe, every single thing, obeys just a few simple laws of physics. There is a reason, and it's usually human error...
**any idea how long the injectors should remain open at idle?**

Now you may be on to something...
**mine are at ~5 milliseconds. Everything points to a rich fuel/air mixture but there seems to be no reason for it.**

Combine that with this statement you made...
** I removed the injectors and had them proffesionally cleaned, injector cleaner is just deisel which p[oured into a 20 gallon gas tank is too diluted to have much effect.**

Learn of what you speak, BEFORE opening your mouth.
It is not diesel fuel in the injector cleaner bottles. Diesel would be illegal to sell, because it would damage the converters, and possibly the soft parts of the fuel system, not to mention the critters living in diesel fuel...

The stuff in the bottles is usually solvent designed to remove the plack that builds up on the injector pintles and seats, and in some cases a microbe killer, to keep the little nasties from breeding in your fuel system.

Has the thought crossed your mind that the so called, "Professional Cleaners" may have screwed up the injectors more than the computer can compensate for?

You need to abandon the injector open time theory, and go to a leakage test, and a volume test for the injectors.

You might want to do an electrical resistance test on the injectors, and on the injection circuit as a whole.

It wouldn't be the first set of injectors that were ruined by some stooge with a reamer or abrasive blaster, posing as a fuel injection man. The clearances in an injector are measured in 1/1,000,000 of an inch. (Millions of an inch.) They are pretty easy to screw up.

Anyone at Strap-On ever stop selling you toys long enough to tell you how a timing light can be used to inspect the injector spray patterns?
How about using an outside pressure source and timed injector trigger to see how much 'fuel' the injector will pass in a pre set time?
How about a graduated beaker to catch and measure the 'fuel' in? (Use mineral spirits)

(The Electronic Fuel Injector Tester is made by OTC (way under $100), and the beaker or baret can be bought at any scientific supply store, and only has to be wide enough to fit the nose of the injector in. The 'fuel' source is an old in tank fuel pump, pumping solvent to clean the injector.)
**Any more advice? **
Take time to think about what is happening, and what ALL of the possible causes would be.
Sir Auther Connon Doyle wrote, "When all other possibilities have been eliminated, what ever is left, how ever improbable, is the truth."

Discussion Starter · #12 ·
The injectors aren't leaking, I have to check the computer ground wire. I've replaced the O2 sensor ~1 year ago. However, it is reading voltage within spec and it does vary lean and rich a little. It tends to stay around .7-.85, .4 is the line between lean and rich. Mine has a camshaft position sensor and a crankshaft position sensor. If they don't send a signal, fuel flow is shut off.

Nick Hagen
1995 Wrangler
33" Mud Tires and a four banger

Discussion Starter · #13 ·
The TPS can't be installed incorrectly, it only turns so far, when you floor it it would break the sensor. The computer is the last thing I'll try, it is more expensive than the sensors and diagnostic work (which is done for free). The Snap-On scanner will read the voltage across the O2 sensor and it reads 0.7-0.85. The cut-off for lean Vs rich is 0.4. Over that is rich and under it is lean. It does vary in it's reading but not much. It acts like the computer doesn't change the mixture ratio even though it knows there is a rich condition. I'll pull the O2 and see what it does, however it seems to run too rich in open loop, at startup if you punch the gas from an idle it stumbles for a few seconds and then finally goes. The injectors have been holding open for 5 milliseconds long before the injectors were cleaned. They have the correct flow rate and I just tried to clean them because that would at least eliminate one possibility of one injector being out of spec, all use similiar amperage to operate. The place I had them cleaned is a place that does it on every tune-up that they do, I couldn't find any complaints about they method, only great praise. The injectors aren't the problem, They flow equal amounts and are very well matched for stock injectors. That cleaner in a bottle is useless, you might as well just throw your money out the window. That's MY opinion, to each his own. If you have any other ideas, let me know. I always appreciate help; however, a less condescending tone would be nice.
Nick Hagen

Nick Hagen
1995 Wrangler
33" Mud Tires and a four banger

Discussion Starter · #14 ·
Nick -
I read the whole thread before something clicked. That's not really surprising since the thread has a wealth of good information in it that caused me to think. (Hard work.) The click at the end was a certain '81 Buick Skylark V6. That was the first year that GM used computers in all of their passenger cars. I went back to the initial post and read the description of the symtoms all over again. It matched my Buick of many years ago to a "T"!!!! Not kidding! It (cat) got so hot that it melted a good camera case and contents in the trunk right above the cat location. The sheet steel case of the cat itself was hot enough to deform just from it's own weight. That means that it probably got white hot or close to it. The reason this can happen is that unburned fuel is burning in the cat. The reasons I got that much unburned fuel in my cat are that I was on a long high speed trip across the Kansas plains in the middle of summer and I kept my foot flat on the floor to make up for the loss of power and stumbling miss and that made the computer give maximum fuel flow. The culprit turned out to be a carbon track in the distriburator from one of the electrodes to a coil attatchment screw base and thence to ground. I never found it myself, a mechanic hired by a wife fed up with me not fixing her car did. I'm older and wiser now and know better than to have an ' 81 GM anything but the principle is still the isn't necessarily the high tech electronic stuff that will cause the rich just might be a simple reason also. I don't think that this is necessarily your problem, but maybe it will get you to thinking.

The amount of talent on this BBS never ceases to amaze me! Where do you get the information about five milliseconds, anyway? That ain't no stopwatch datum!

You do understand that you are now obligated to keep us all completely informed as to the future of the problem and that includes diagnoses and treatments and prognoses!


· Registered
13,180 Posts
In my last post I had hoped to lead you to conclude the problem was happening in Open or Closed loop or both... to me it was not clear. From your last post it seems, if I read correctly, the problem exists in Open Loop. The O2 Sensor is out of the loop during Open Loop, as are lots of other stuff. That's why it is important to know when the problem occurs.

By eliminating the Closed loop monitoring the casuse can be brought back to some elememtal items only active during Open Loop.

To be running rich in open loop only a few conditions can exist;
a. The injectors are being held open too long.
b. The fuel rate past the injectors is to high per the time thier open.
c. There is not enough air in the mixture.

Item C can probably be crossed off the list.. as you've checked for vacuum leakage, etc. and the air flow has not been restricted in any way.

That bring us back to Items a) and b).

Because there are no comptuer codes being thrown, this in itslef could be a clue. Does the computer throw a code for too High a fuel Pressure? This would be different than a code for a faulty pressure regulator.

You said the fuel rate was in normal paremeters when the injectors were cleaned and tested.. This tells us that the injectors open and close per spec. Good news!

I have to assume the injector on time pulse is correct. This timing is a set time while in open loop and it is controlled by the computer.

The only other varriable left that I can think of is the fuel flow rate past the open injector pintel during on time.

Flow rate is determined by fuel pressure. Regulating the pressure to the injectors is the job of the pressure regulator. It takes the incomming fuel at the higher line pressure delivered by the pump and delivers it at a lowered pressure to the injectors.

Excess fuel is diverted back to the gas tank through a relief line.

Test the relief line by unhnoking that line and diverting the fuel into a gas can aside the Jeep. It will come out fast, so be prepared. If the problem goes away, you know the relief line or the regulator is at fault.

I'e not heard a lot of talk about fuel pressure as yet, and that requires a fuel pressure meter. Measure the input flow and the relief flow to see if they are in spec.

Nick you said: "I always appreciate help; however, a less condescending tone would be nice." That's an oxymoronish statement. There ain't no shame in asking for more help, but there is shame in giving thoes who offer unkind remarks.

If you want more help, a simle thank you will do quite nicely. IF you do not want more help, a simple thank you will do...

As you know, trying to help other out virtually is not easy, give the guys a little credit who are trying to help you by imparting their sills and knowledge to you...their not trying to show you thier smart and you're stupid. That would be a foolish waste their time. Don't furhter waste yours, or theirs.

I'll chalk your remark one up to frustration and not a lack of civility. Again a simple thank you will suffice.

Good Jeepin'


Discussion Starter · #16 ·
In open loop on some mornings, it runs bad. In closed loop is when it backfires between shifts, misfires randomly during acceleration, runs too rich, and just seems like it tries to flood out. Thanks for the help,
Nick Hagen

Nick Hagen
1995 Wrangler
33" Mud Tires and a four banger

· Registered
13,180 Posts

Sorry, I gotta read your posts better, I missed the Fuel Pressure stuff. Aaron at TeamRush makes a lot of good points. I wish I had his understanding of Fuel Injection. But it seems something is being overlooked, or missed. I don't have a lot of sophticated equipment to test with, the kids like to eat, so I try to do everything as inexpensivly as possible.

IS the fuel pressure in spec? And is that the pressure delived to the injectors? If so, I'll quit beating a dead horse. If it's the input pressure, then we still don't know how much is delivered to the injectors. Then it's time to measure the relif pressure, subtract from the input pressure and that should be about the pressure delivered to the injectors.

Otherwise, IMHO, it's time to start again at the basics and write down your findings to insure nothing is overlooked. It always helps me when I make a chart such as:

Sensor Name | Voltage Reading, high to Low| Resistance, Cold to Hot| OK? |

Then I start pulling the sensors, clean and bench test them and mark the results. Since the O2 sensor is a year old let's start there..

The O2 sensor fins must be free from any build up. If the fins are clogged, the sensor will not perform accuratly. It may however, fall within the normal voltage parameters. In short, it can trick you to thinking it's good when it's not.

Tools needed:

1. Propane torch.
2. Locking Pliers (I like vice grips).
3. VoltMeter (Analog: 10 meg ohm imput impedaance)
(Digital: 10k ohm imput impedance)


1. Connect the meter leads accross the sensor wiring if it's a two wire sensor. If it's ony got one wire then one lead the wire, and the other to the sensor case (ground).

2. Set the meter to read milivolts.

3. Clean the 02 sensor fins.
Heat the tip of the 02 sensor so that the flame enters the fins, and the tip turns to a dull to hot red colour.

4. The O2 sensor should produce a small voltage. Is the Ohm reading over about 600 mv?
If you move the flame, does the mv reading change quickly?
If so, then the O2 sensor is OK
If not, then replace the O2 sensor.

Idle Air Control:

The IAC is just a solenoid that responds to the Compuers signals. Remove the IAC and use some good carb cleaner to clean all the passages and the pintle. Make sure it moves VERY freely before you reinstall it.


1. Remove the TPS.
2. Set the leads of the VoltMeter to K Ohoms.
3. Measure the Ohm value of the TPS while slowly turning the TPS wiper. Does the Ohm value drop out? The TPS could be dirty inside and the wiper may not always make contact.


As far as I know there ain't no "Cheap" way to test this out of the car. I take mine to NAPA and have them throw it on their sensor Testors. But this sensor is does a lot of stuff real fast when it reacts to manifold pressure. I trust the NAPA test about as far as I can throw it. If you can substitute the sensor for a known good one that's the best test.


Aaron is right about the compuer possibly being bad. When it is very wierd symptos can occour. A computer can sometimes be tested with the factory voltage tests and Ohm tests, and by thier scopes. Do you have any way to determing the quality of the computer? If not, this is sure one BIG single point of failure.

As for the timing issue, it's pretty easy to see if the timing gears/belts are OK, try this:

1. Remove the distributor cap.
2. Put a socket and ratchet on the cranshaft pully bolt.
3. Have a friend note the position of the distributor rotor.
4. You note the position of the ratchet handle.
5. Start to turn the enine by hand.
6. Have your friend yell when the distributor rotor starts to move.
7. Stop turning over the engine.
8. Note the position of the ratchet handle.

If there is more than about 6 degrees of movement, the distributor gear, or the timing gears are worn and should be replaced.

That's all I can Think of right now... let us know more...

Good Jeepin'


· Registered
6,784 Posts
Thanks for the good words LEVE!
We could have used someone as methodical as you when we started our aftermarket fuel injection company back in '84. We had the hardest time finding people that would stay with a problem long enough to figure it out.
Most people want to make a surface inspection, declare this, that, or whatever OK, and jump to something else. No one wants to 'Flick the fly sh*t out of the pepper' as it were.

I would not tell him what was wrong now even if I was sure what was wrong. If he quits bashing me and companies that know what they are doing long enough to THINK....
This really isn't that hard, but it's just easier to blame everyone else than to get a half a dozen brain cells to work together...

Nick is doing OK by himself, just ask him...
He deleted the catalytic converter (a federal offense), and declared the exhaust system OK.
(IF the converter was bad, what made the converter give up? Has he ever seen double wall head pipe, with the inside tube collapsed?)
He gave a cursory inspection to some sensors, and declared them OK...
(How did he verify the sensors? How about the sensor connectors and wiring harnesses?)
He gave a cursory inspection to timing/ ignition systems and declared them OK.
(How did he verify the timing/ ignition systems?)
Then he jumped to the IAC, then to the MAP, then to the TPS again...
(Always an easy target when things get frustrating...)
If everything is OK, then it should be running great.
(Surprise! It's not, so something got missed... AGAIN! Time to stop bashing respectable companies, with engineers that know what they are doing, and stop bashing products you don't understand, and do your homework...NICK...)

Here is something to think about, Nick said it was 'backfiring'... Is it 'sneezing' up through the intake, or 'popping' down through the exhaust?
If it is the exhaust, it's almost always ignition. What does the ignition trigger look like?
If it is intake, it's almost always fuel metering. (excluding bent or burned intake valves, or ignition timing so screwed up it's firing while the intake valve is still open, or when some genius bundles the plug wires together and it induction crossfire happens)
There are some exceptions to the rule (which I'm sure I'm going to hear about...), but this is a pretty good guideline.

BTW, there is adjustment in EVERY TPS mounting, there has to be to correct for manufacturing variations and resistance in the wiring and connectors.
The TPS is critical in every closed or open loop system, and it has to be calibrated correctly, or you engine thinks the throttle is opened, assumes the MAP sensor and/ or the O2 sensor has failed, and works as a speed/ density system, and adds more fuel.
Every system goes rich instead of lean to save the engine...

Have you checked/ replaced the water temperature sensor, and (if it has one) ambient air temp sensor? I didn't see anything about it here. If the temp sensors don't agree, (and there will be at least two) then the system thinks it's too cold of a day to register correctly, and adds fuel for the 'choke' effect. This can also keep the engine in the 'warm up mode' about 5 to 14% rich, in most cases.

The rule of thumb in working on any closed loop fuel injection system is, with O2 sensors, have a pair and a spare. The same goes for MAP sensors. There is so much that can kill a O2 sensor that extras are mandatory in a diagnostic shop.
Fuel 'Drying' additives, many 'Octane Boosters', several types of gasket sealer and gasket maker, tack cote to hold gaskets in place, and about a thousand other common engine products will kill an O2 sensor, or worse, impede it's function.
I suspect the O2 sensor in your engine has failed, but I don't think that is the problem here...

The digital fuel injection we sold to a customer for a blown big block drove us crazy trying to figure out what was wrong, and it turned out that the factory had slipped in a regular 2 bar map sensor, instead of the 3 bar that was supposed to be in the box...
Another time the guy laid the injector harness next to the SOLID CORE plug wires...
Another time a guy had the flywheel trigger actually touching the teeth...
Another time a guy had is crank trigger firing on the triggers and the mounting bolts...
Another time the guy had decided to add extra injectors to the system...
Another time we got a batch of bad O2 sensors...
Another time we got a bad batch of injectors...
...and the list goes on... It's just life on planet earth.

If you don't know how to verify every part in the system, take it to someone that can.
If you can't or won't verify the wiring harness, take it to someone that can.
If you can't stop to think it through, take it to someone that can.

So many cats, so few recipes...

· Registered
1,736 Posts
Nah, I gotta be with Nick on this one, dudes. Great answer by TR, and the guy seems to know his stuff, no question about that, but the words did seem a little strong to me too. Granted, a tone-of-voice is difficult to get across via this medium, and he could have just been trying to give him a fake punch to the gut /wwwthreads_images/icons/smile.gif but some of us are not as smart as some of the rest of us. ...kinda why we're here. No reason to belittle those of us who don't run, own, or work for "aftermarket fuel injection companies." I think Nick took it in stride, and thanked you for your help, and for your continued help, and asked very politely if you could use a better tone. If you can't help the guy without belittling him, what's the point?

fake punch to the gut back at ya /wwwthreads_images/icons/smile.gif

88YJ, 4"susp, 33"BFGMT, 9k#winch, rear homemade swingout, reb.258, 999, 4.10, weber32/36, GMHEI.

Discussion Starter · #20 ·
You have to appreciate the maturaty on this BBS. I says a lot when we can take what we dish out. But now, back to the problem....damn, you guys know a lot...I'm just glad I know how long 5 msec really is.

Based on all the input, my gut feeling is mechanical timming and the computer is trying like hell to compensate. I would at least verify that its may have to pull the valve cover to verify when the valves open as related to TDC.

John......southern CA
84CJ7, 3"lift, 32"BFG, 4.10's, ARB Locker, Solid Axle's, Durabak
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