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help with a 2.5L

2K views 19 replies 1 participant last post by  **DONOTDELETE** 
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#1 ·
I need some help with my 85 S-15 2.5L engine. It seems to run rich and I can't get the timing right. When I adjust the timing to 8 deg it tries to die out on me. I have to run the timing way high for it to even run good at all. I have checked for vacuum leaks and can't find any. The injector seems to spray too much fuel but I dont know how to correct it. The O2 sensor looks original. Maybe that could be causing the problem? Any advice would be apreciated!

92 S-10 Blazer 4x4 Vortec 4.3
85 S-15 Pickup 4x4 2.5 iron duke
 
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#2 ·
Hey Fredbear, listen this happened to me last month, in mine I changed the map sensor, plugs and wires, oxegen sensor, TB gasket, ERG valve, I was feed up of changing parts and nothing was changing, so I went to a garage to get the computer analized and presto ... all my problem was, was lean fuel pressure so I changed the fuel pump and it runs like a charm. It`s like you said I was running bad, I couldn`t time it it would die out on me on the mark. so check out your fuel pump.

I`d rather push a Chev than drive a Ford
Hachey, 88 Blazer 4x4
 
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#3 ·
yea but mine is running rich not lean. I think the O2 sensor may be bad. When the engine is running and I look at the injector it seems to be putting too much fuel to it. If I unplug the vacuum lines at the charcol canistier a little raw fuel runs out. This would indicate too much fuel allso. I think that it may be a bad O2 sensor but I was just wanting some advise. Thanks for your advise but I dont think that that is my particular problem. I have the exact oppisite problem. Too much fuel.

92 S-10 Blazer 4x4 Vortec 4.3
85 S-15 Pickup 4x4 2.5 iron duke
 
G
#4 ·
CHECK OUT YOUR VACUME LINES, I DO KNOW THAT WHEN MY VACUME LINE FOR MY MAP SENSOR IS OFF, IT IDLES VERY HIGH AND DRIVES REALLY BAD MAYBE PLAY WITH THAT UNPLUG IT AND SEE IF THERE IS SOMETHING IN THE LINE ITSELF BLOCKING THE VACUME. MY TRUCK IS AN 88 AND I CHANGED A LOT OF MY LINES ALREADY BECAUSE OF VACUME LEAKS

I`d rather push a Chev than drive a Ford
Hachey, 88 Blazer 4x4
 
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#5 ·
silly question: when you try to adj the timing are you disconecting the tan wire under
the glove box?

HAWG WILD
ALL THOSE WHO WANDER ARE NOT NECESSARLY LOST /wwwthreads_images/icons/cool.gif
 
G
#6 ·
no! what tan wire? I know that on older conventional engines you have to disconect the vacuum advance but this engine has no vacuum advance. So do I have to disconect a tan wire under the glove box? Where is it exactly?

92 S-10 Blazer 4x4 Vortec 4.3
85 S-15 Pickup 4x4 2.5 iron duke
 
#7 ·
Since you don't know the age of the O2 sensor it's probably good to make the expense and change it out. That silly little frickin' sensor lead is the main cause of a lot of frustration.

Another cause might be faulty injectors. You might want to consider having them cleaned out or rebuilt/replaced. Try the cheaper stuff first and see what you get from there.

Hope that helps.

/wwwthreads_images/icons/shocked.gif- J.R. -/wwwthreads_images/icons/shocked.gif
 
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#8 ·
Yup, those O2 sensors can be a real pain the the as$. That would be the first thing I would check. I replaced mine after failing emmisions, it ran great...for about 2 weeks. Then, the check engine light became what I called the JFK eternal flame. The brainchild at the autoparts store gave me the wrong one.

 
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#9 ·
the reason why there is no vacuum hose is that EST (Electronic Spark Timing)
controls all of the timing ( i.e. no vac adv or centrifugal weights). I was off slightly, later
models have the tan wire, what you need to do is jumper the A/B terminals of the ALDL
connector (screwed to the bottom panel about where your right knee is)the A term is the
one in the upper right corner and the B term is the one to the left.
(THIS IS FOR MOST S/T TRUCKS, LOOK AT IT IT SHOULD BE MARKED)
___________
|F|E|D|C|B|A|
|-----------------|
|G|H|J|K|L|M|
-------------------
Jump the two terminals together with the ignition OFF, this will over ride the EST module
and let you set base timing. by the way if you do this with the ignition on, it should flash
the CHK ENG light 12 times (diagnostic mode) or flash out trouble codes (i.e. O2 sensor)
(get a good service manual for diagnostic codes)
happy wrenching

HAWG WILD
ALL THOSE WHO WANDER ARE NOT NECESSARLY LOST /wwwthreads_images/icons/cool.gif
 
G
#10 ·
Sounds like you're truck is having the same problems my wife's Nissan Sentra has. For the last year or so, her car has shown horrible accelearation. It hardly accelerates at low rpms and then literally jumps up to speed at a certain rpm (no tachometer so I don't know exactly when). I tried a tune-up and $15 fuel injection cleaner, but neither helped. The vacuum hoses all look fine and are connected, and the motor runs great except for the acceleration problem. Also, the car's oil smells like gas every time I change it. This and some other stuff led me to believe the carb is running too rich.

I was going to change the air/fuel intake ratio, but I came to find out that it is all computerized. Fortunately, a salesperson/ex-mechanic informed me that if the O2 sensor goes out, the computer won't mix enough air because the computer thinks the engine is getting more oxygen than it really is. I called the Nissan service center and they confirmed this. Unfortunately, the sensor costs $70, but if it works, it's more than worth it.

Of course, my wife's Sentra doesn't have the timing problems you mentioned. Also, the lifetime on an O2 sensor is around 100,000 miles, so if your truck has considerably lower miles, I'd look elsewhere first. In any case, I'm ordering the sensor this Sunday. I should have it changed in two weeks or so and I'll post how it went for future reference. If you replace yours in that time, please let me know how it went.

/wwwthreads_images/icons/cool.gif Steven Fairchild /wwwthreads_images/icons/cool.gif
/wwwthreads_images/icons/wink.gif 96' S-10 4x4 /wwwthreads_images/icons/wink.gif
 
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#11 ·
let me try and better discribe what's going on, without writing a book:
EFI systems have two modes OPEN LOOP and CLOSED LOOP

OPEN LOOP: generaly when cold, before the cat heats up, the ECM(brain)
retards the timing and richens the mixture to help get the system up to
operating temp as quick as possable.While it does this it ignores all input
from allmost all the sensors.

CLOSED LOOP: as the cat, engine temp and O2 sensor heat up the system
switches to closed loop, which adj the air/fuel ratio automaticly to lower emmision
and produce more power on less fuel.

when the O2 sensor is not sending the correct info to the brain, the system
never goes to closed loop and runs way rich all the time. this is why you can smell fuel in
the crankcase, the realy bad part is that it washs the cylinders and strips the
oil from the rings(not a good thing) causing serious wear/damage. the other
bad thing is the acids and other nasties you get in the lubricating system. If
any of the critical sensors fail the system automatical goes to open loop and
sets the check engine light(limp home mode) and all you realy notice is performance
sucks. O2 sensor is guilty alot but theres 5-10 other sensors in the sys too.
MORAL TO THIS STORY: find out what set the light and fix it.
happy wrenching

HAWG WILD
ALL THOSE WHO WANDER ARE NOT NECESSARLY LOST /wwwthreads_images/icons/cool.gif
 
G
#12 ·
ok, Today I replaced the O2 sensor and man what a differance. My instincts were right. The check engine light never came on but I suspect this is because the engine allways told the ecm that it was cold and to run in the rich mode. The sensor (a bosch) cost me $17.95 at Auto Zone.

92 S-10 Blazer 4x4 Vortec 4.3
85 S-15 Pickup 4x4 2.5 iron duke
 
G
#13 ·
I know all of this great info but-- my ALDL connector has no wires going to the top row. I dont want to try and go to the bottom row in fear I may short the ECM out. The manual and you tell me to jump teminal A to B but I have no wire in A or B. I see no apparant signs of anyone messing with this connector so I dont understand why I dont see wires in the top row. I did replace the O2 sensor and it made a big differance but now I need to go back and adjust the ignition timing. No engine check light ever came on and I suspect that the ecm was allways operating in the closed mode because it was running rich. Do I have to jump A to B to over ride the advance and adjust the timing? Any ideas?

92 S-10 Blazer 4x4 Vortec 4.3
85 S-15 Pickup 4x4 2.5 iron duke
 
G
#15 ·
OK, now ya got me scratchin my head. I pulled down the elect diagram books
and found some strange stuff. According to the book the 2.5(fed emissions)
has a vacuum advance and the 2.5(Cal emissions)uses EST, also the fed emission
truck doesn't even have an ALDL connector(according to my book),sooo I'll take a
shot in the dark-you probably have a Califorina truck(good guess or not??) or the general
made a mid year design change because all 86 and up have EST.That still
doesn't explain why there is no A/B wires. Here's a couple things that might help:
1)The A wire on my truck is black/white and the B wire is white/black-but mines an 87
2)according to the 85 Cal emissions diagram there IS a tan wire that runs to ground
(late model style)so on the passenger side,pull the black plastic panel under the
dash off and see if there is a tan wire running all by it self with a connector in it,
that is the one you need to disconect to disable the EST.

let me know if that helps if not I'll go back to banging my head on the wall
(it help me think-but starts to hurt after a while)

HAWG WILD
ALL THOSE WHO WANDER ARE NOT NECESSARLY LOST /wwwthreads_images/icons/cool.gif
 
G
#16 ·
ok I will look and see if my truck is a california truck but I dont think it is. I will look for the tan wire and let you know. Thanks for the great information. But I have another question. When I got the truck the exahst was broken and burnt the vacuum lines for the front diff in half. I need to find out what line goes to what. Can you help me on this one?

92 S-10 Blazer 4x4 Vortec 4.3
85 S-15 Pickup 4x4 2.5 iron duke
 
G
#17 ·
yes and no,If memory serves me there are three hoses. The large
diameter one it the t-case vent. The two smaller ones, one is vacuum
source the other is signal to the accuator. I don't THINK (not positive)
it will make any diffrence if the vac is reversed because it a mechanical
valve and will flow either way. hope it helps

HAWG WILD
ALL THOSE WHO WANDER ARE NOT NECESSARLY LOST /wwwthreads_images/icons/cool.gif
 
G
#18 ·
ok I checked it out and here is what I have. My connector only has 4 wires in it. on the bottom row to the very left it starts with a black wire with a white stripe then the next connector to the right is a white wire with a black stripe. then it skips 2 and the 5th hole from the left has a orange wire and the last one on the bottom to the right is tan with a black stripe. I have no wires in the top row and I found no tan wire under the glove box. Can I just jump the wires in the bottom row to the left? Or will this fry my ECM? HELP!!!!


92 S-10 Blazer 4x4 Vortec 4.3
85 S-15 Pickup 4x4 2.5 iron duke
 
G
#19 ·
I figured it out!!!!!!!!!! The picture you gave me and the one in my manual were upside down. Or my ALDL is upside down. Anyway on mine the A and B terminal is in the lower left corner of the connector. I got the timing adjusted and the engine runs good. I also was able to fix my vacuum hoses to the front diff and now I've got 4 wheel drive. Thanks for the help this has been a lifesaver. Now I'm going rabbit hunting in the morning!!!!!!!!!!!

92 S-10 Blazer 4x4 Vortec 4.3
85 S-15 Pickup 4x4 2.5 iron duke
 
G
#20 ·
/wwwthreads_images/icons/cool.gif/wwwthreads_images/icons/cool.gif/wwwthreads_images/icons/cool.gifcool/wwwthreads_images/icons/cool.gif/wwwthreads_images/icons/cool.gif/wwwthreads_images/icons/cool.gif
HAPPY HUNTING

HAWG WILD
ALL THOSE WHO WANDER ARE NOT NECESSARLY LOST /wwwthreads_images/icons/cool.gif
 
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