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Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

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post #1 of (permalink) Old 04-27-2007, 02:04 AM Thread Starter
 
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YJ frustration

I have an 87 YJ which I just had the engine rebuilt on. It also has a Holly Projection 1D TBI conversion.

Ok so I can't get the thing to run right and I'm not sure where to look. The main issue is that after the engine has been running rigorously for a while- it bogs. So it starts out fine and the first half hour of driving is good but then at some point it stops working well. It bogs between 1,000 and 3,000 rpm and the rpm where it bogs seems to get lower the longer you use it.
Hence- it seems to be temperature related but I'm not sure. I have taken temp readings with a gun and the engine is never over 200 [so I dont' think it's overheating] but maybe the temp sensor for the Injector ECM is bad...

Ok so ideas I've had:

Temp sensor for injector ecm is bad.
The fuel is too rich or too lean (but could this cause my symptoms? IE performance is bad after it has been running for a while).
The timing of the engine is off.

Other possibilities? injector is bad? I don't think the throttle sensor is bad- I checked it.

Does anyone have any ideas about what I might look at? I really just want to get the Jeep purring nicely and ready for offroad.

Thanks
-Vindication
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post #2 of (permalink) Old 04-27-2007, 09:00 AM
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Rather than try to blame a specific component (shotgunning) just yet - that would take a good guess - or possibly lots of guesses and lots of money, lets find out why, or at least the area. Then a little further testing can find the component.

Back to basics - fuel or timing?

Get it to do it - then check the timing advance - at low, mwedium, and high speeds - especially in the problem RPM range. Compare it with the same readings when it doesn't act up.

And - do a search for "propane trick" - make the device ($10?) - then try giving it propane when it's acting up. The propane will will supplement the fuel - making it richer, if the problem does not change away you know it's NOT fuel related - rich/lean etc..
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post #3 of (permalink) Old 04-27-2007, 11:30 AM Thread Starter
 
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Thanks RRich-

One problem w/ both things you suggest is that the engine only has the problem under load. So I can work it up to having the problem but if I'm parked in neutral it will rev up fine.

Maybe I should just play with the advance and see what the result is...

Also the engine has an oxygen sensor-- does anyone know how to tell if I'm rich/lean by looking at a voltmeter? I can buy a rich/lean indicator that hooks up to it for $100 but seems pretty stupid as it just looks at the voltage from the O2 sensor.

-Vind
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post #4 of (permalink) Old 04-27-2007, 11:42 AM
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That makes it more difficult to watch the timing under load - but if the timing curve is wrong, it can act up only under load but still be obvious unloaded. Check it anyway.

Make sure the distributor is running on Ported Vacuum, not Manifold Vacuum. Just that alone can cause your symptoms.
If it's EST - Electronic Spark Timing - it's a different story, but probably NOT the problem.

Look at the "propane trick" post - it addresses that - easy to do.
The propane can easily be done under load - hold the valve and small bottle in your lap with the hose running into the air cleaner - 6 foot hose. Drive it - put it under as much load as it takes to make it act up, hold the bottle upside down to get liquid (valve at the top - vapor -won't get enough propane out,) open the valve a little - the propane richens the mixture.

Before throwing lots of parts at it - it's usually much cheaper and easier to know WHAT parts to throw!
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post #5 of (permalink) Old 04-27-2007, 03:29 PM
 
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Unfortunately the few times I've heard about the Holley system is from those who can't seem to get it to work right. Rich, lean, what's the difference if the system is not adjustable. Its either broken, and you have to find the faulty part(s) or it never did work right from the factory.

My inclination would be to put a Motorcraft 2100 carb on it if that's legal and enjoy trouble free operation for around $200.00. Sorry if thats a blockhead response to a question about fixing your fuel injection system.

Did it ever run right with the Holley system? What's the history of the rebuilt engine and this system? When did they come together? Have you changed / altered anything else on this motor? Does Holley use generic sensors or are they proprietary Holley parts?

Last edited by TiminMb; 04-27-2007 at 03:31 PM.
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post #6 of (permalink) Old 04-27-2007, 04:08 PM Thread Starter
 
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Why do you say can't adjust it? The ECU allows me to rich/lean the mixture with a control knob. Now if you mean it does have a lot of adjustment (much freedom) then I can agree.

As far as the history- before the engine was rebuilt it worked GREAT with the holley. It had plenty of power, always started, and never stalled. So I know it's capable of getting there... I didn't install the system or tune it originally- it was like that when I bought it. The previous owner told me it was a real pain to get it tuned right and told me to never adjust it. LOL. Well after the rebuild it needed to be retuned.

Not sure about all the sensors. Here's a link to the installation manual if anyone is interested.

http://www.holley.com/data/TechServi...al/R9895-3.pdf

It tells about the parts in it.
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post #7 of (permalink) Old 04-27-2007, 04:14 PM Thread Starter
 
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RRich-

Not sure about the vacuum advance. Attached is a picture of my throttle body. Right now the vacuum advance tube is connected to the port labeled timed spark.

Ok couldn't figure out how to attach the image w/o making it look like crap. I apologize.

-Vind
Attached Images
File Type: gif 1d-tbi_3.gif (77.6 KB, 81 views)

Last edited by Vindication; 04-27-2007 at 04:22 PM.
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post #8 of (permalink) Old 04-27-2007, 06:03 PM
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Usually the "adjustment" on those is only slight - it's just Fine Tuning.

FIRST you need to determine IF it's a fuel or Ignition problem. THEN you track down WHAT component is faulty - IF one is, or what is CAUSING it.
There are probably 3 dozen items/reasons WHY you are having trouble. But probably only ONE is causing it.

Questions - the distributor is connected to a vacuum source that has very little or 0 vacuum at idle, then slowly increases with RPM? That's ported spark vacuum - no matter what a label says - check it!

Make sure it is really getting to the distributor.

And - check base timing - vacuum disconnected - it should be around 8.

Check total timing at 1500 RPM, again at 2000, and at 2500 RPM. Tell us what it is. Too fast, too soon, or too much can cause your stumbles.

Plugs - you ARE using the STOCK ORIGINAL BRAND AND PART NUMBER plugs, not junk aftermarket parts houses love to sell because they make more $. Are you? Wrong or Mickey Mouse plugs can do it - especially since you say it gets worse warm.
No splits, plats, multi's, Kraut, Jap, or any other gimmick plugs. Use what the designers of the head designed the head around. Look in the book!

Contrary to popular belief - what type of fuel system, or what generates the spark has NO BEARING on how the plugs act in the combustion chamber. They don't get longer, change heat ranges, or change indexing just because you have a different coil or carburetor.

Don't go throwing parts at it - changing stuff arbitrarily will not do much more than changing tire pressure will help. (But a couple of STP stickers might.)

It ran fine once, it can again.

Do it and report back for the next step(s.)
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post #9 of (permalink) Old 04-27-2007, 06:13 PM
 
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Well, if it rain properly at one time, that's encouraging.
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post #10 of (permalink) Old 04-27-2007, 06:32 PM Thread Starter
 
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There is no vacuum to the advance at idle. Raising rpm does create suck. So it looks like it is ported vacuum advance.
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