Topic: Help with 89 YJ 2.5 TBI missing on cylinders 3 & 4 at

[Erik]

at idle cylinders 3 and 4 are missing... i can pull their plug wires with the engine running and it has no effect on idle.

i replaced the distributor thinking the shaft might have been bent, i replaced the coil, i replaced the dizzy cap, the dizzy rotor button, and the plug wires.   undoubtably i have a much stronger spark but still no combustion.

once i hit the gas it sputters slightly but then it's fine... it drives just fine as well.  so, once the rpm's get above idle, all 4 cylinders are running fine... this just happens at idle.

is it possible cylinders 3 and 4 are not getting fuel?  is there a way to test this?  has anyone ever had a similar problem?

thanks in advance.

-Erik  <--- REALLY aggrevated

[Jeffy]

Have you checked for spark at the cylinders?  How about the pickup in the distributor?  Do you know which cylinders aren't firing?  If they aren't firing, and fuel is still getting to the cylinders, the plugs might be damp.

I don't think it's the CPS since you said it is fine when you rev it.  I'd probably still suspect something between the distributor and the cylinders.

[Erik]

cps?

i thought along those same lines but after pulling the plugs i'm finding that 1 & 2 are covered in carbon/soot/black while 3 & 4 look perfect and just as clean as a properly running car's plugs should.

i have strong spark at every plug and have tries swapping plugs around with no change in idle.  i also checked gap and they were perfect.  i really think the fuel isn't making it back there to 3 & 4.... but i don't know why that woudl happen.... vacuum related?  egr related?

i have all my egr stuff removed except the valve itself, and i have all my vacuum lines (the hardlines that line the back of the engine and feed from the 4 ports on the throttle body) removed and replaced with individual lines going to MAP, 4WD, PCV, and the 4th is blocked with a nipple.  

i'm going to do a compression test tomorrow afternoon.  i've got my fingers crossed that i don't find a problem there... i can't afford to pull this thing apart and re-ring it... and it doesn't smoke so... i dunno....

would there be any reason for me to remove the throttle body?  it's not like i could see anything from just looking at it that woudl cause a problem right?  maybe if i removed the TB i could unbolt the EGR valve and block that off.... that woudl eliminate another possible voacuum leak....


think guys, i'm really stuck here....  if you have any ideas, i'm all ears but as i've said, the ignition is now, totally new, everything, and i have great spark on all 4 plugs... just no fuel on 3 & 4 AT IDLE....

-Erik

[chrisfranklin]

Longshot, but, maybe there's an intake gasket leak around 3 and 4. Its an '89, so maybe some deterioration has occurred.  Could be enough to keep those 2 cylinders from lighting at idle, but under throttle, all 4 hit.

I'm guessing you would have spotted a "leak" already, though. And, then you would have sprayed some carb cleaner or oil (to potentially seal it) on the gasket just to see if 3 and 4 fire at idle for a short while.

[Erik]

i have no carb cleaner so i haven't tried that yet... but it makes sense....   i'll try that this afternoon.... might just replace the tb and intake mani gaskets and see what happens.... how hard can it be......



also...

when i replaced the fuel filter and cleaned the tank i blew out all the lines, don't know if that matters... but it did this before i cleaned all the fuel system anyway....



when i put in my new dizzy i had #1 at top dead center.  the oil pump gear or whatever it is that drives the dizzy was at about 3 o'clock if i remember right.  when i installed the dizzy the contact on the rotor button was dead on the #1 spark plug contact on the dizzy cap.  according to eveything i have read that is all correct.



i dind't build this motor but it was rebuilt.  when i bought the jeep it didn't idle like this.  is it possible that the cam timing is off?  i know i've skipped timing on a timing belt before... but never heard about timing chains and skipping timing.....



this afternoon when i get back from raleigh i'm going to do a compression test and i'll put a timing light on it.



any more suggestions?



thanks



Erik

[Erik]

any help would be great...

[Jeffy]

Even the TBI engines have computer controlled timing so either you're 180* off and it doesn't run or it it runs and is able to adjust itself.

You might want to check the timing chain.  If it was original when the engine was rebuilt it could have loosened up.  I believe there is a tensioner on there too.

As for the CPS, it's the crank position sensor.  Basically tells the comptuer when it should fire the cylinders.

Have you tried to recover any error codes from the computer?  That would help narrow down the problem.

[Erik]

good suggestions

no i haven't tried to pull any codes.  it was my understanding from another forum that on the 89 yj i couldn't pull codes.  if that was false then i'm listening with open ears as to how i can do it...

i know it's throwing a lot of codes... it has to... i've removed all the vacuum "stuff" except 4WD, MAP, and PCV......   i should be able to see which codes are relevant to my problem though....

-Erik

[Erik]

compression test shows:

cyl 4 115psi
cyl 3 135psi
cyl 2 120psi
cyl 1 120psi

anyone?  suggestions?

[Erik]

new computer fixed it.  cost $65

[davids89YJ]

Good to hear, i like it when people post their solutions. Now I know if I ever come across that issue. I'll be sure to check it out.

[Erik]

well it's got more new issues now... i'll post details on that next... it's interesting to say the least....

-Erik <--- will give you one hint....

[Jeffy]

Nice, open headers...  Must be loud.  Don't put the cat back on unless you want melted cat.

[Erik]

thats not out of the header... that's out of my piping....  i have a banks header, i think, to a 2.5" pipe, to a 22" resonator, to a 2.5" pipe that ends with a 90 before the gas tank.....  no cat or muffler.... muffler coming soon...