Hey there,

Got a problem that seems more iritating than anything else.

1989 IROC 5.7 - had to do the head gaskests last summer. Had most of the engine apart. All is back together. Car starts great and runs fairly well. There is however a small stumble (vibration)when you first accelerate (just off idle) but only under load (when car is in gear). It does not seem to be a problem when car is not in gear meaning you hit the accelerator and get good throttle response. The stumble only seems to happen when you accelerate normally. If I nail it, it responds as expected.

When under small to no load at road speed 40-50 MPH in 4th gear the same kinda thing happens, the engine seems to virbrate or what some might call, "pulse". It is almost like it has a resonance. If I drive in 3rd gear (drive) it seems ok. Only when I let it go into Overdrive (4th) do I have the problem. Once I hit higher speeds in 4th it is ok as well.

I am getting no codes at all, I have checked and rechecked the spark plug wires and firing order. Rechecked all the intake bolts for tightness.

I am thinking that it may be a bad EGR, or something that did not get reconnected properly. Maybe it is the timing (I had the distributor out and back in to do the head gaskets). One other thought or more of a quesiton is the fuel injector connections. I labeled the wires and the injectors that they came from when I took the engine apart but with the dirt and grease, the lables were less readable than I had anticpated when it came time to put them back on. They are grouped in pairs and from what I can read on-line, it seems that the injectors are pulsed all at one time for each side of the engine. Can someone confirm that there is no real "firing order" for the injectors.

Thanks,

Rick,
89 IROC 5.7 TPI
Flowmaster Cat Back.
Accel Ignition.
K&N
Factory Leather

 

The injectors are all fired at the same time (called "batch fire"), so the order they are plugged in doesn't matter at all. You're fine on that front.

If you've had the distributor out and not checked the timing since replacing it, that should be your very first thing to do. NEVER pull a distributor without checking the timing when you reinstall it. It is physically impossible to get it back exactly right. Timing always needs to be checked after installing a distributor.

See if you have any problems after checking the timing and get back to us, okay?

- Vern

 

Thanks Vern,

Any ideas on a "do it yourself" way to check the timing? Any posts?

Rick

 

You should probably do a search, but since this is pretty short to describe, I won't "make" you do it this time....

First - Turn off the motor and disconnect the ESC wire over by the passenger's side strut tower. It's a single brown wire with a circular/tubular connector. Hook up your timing light to the #1 spark plug wire and battery. Instructions for that come with the timing light you need to have/borrow/buy/etc.

Find your timing pointer on the upper driver's side of the crank pulley. Should be some lines marked on it. Find the one for six degrees and put a little chalk or fingernail polish there. May have ti use a rag to clean it off a little bit first. If you don't see any marks, bump the motor over a couple of times until you do.

Then start the motor and point the timing light at the crank pulley and see where the mark is in relation to the pointer. If not exactly lined up, loosen the distributor bolt a little bit and very slowly turn the distributor a little bit at a time until they do line up. Hold the distributor from the sides (not the top) to try and avoid getting a spark wire shock (those smart!!!) Also make sure your other hand is not touching anything metal while turning the distributor to help avoid those jolts. Then tighten down the distributor and recheck it. Somethimes it shifts a little when you tighten it down.

Once they are lined up when the motor is running, shut it off, remove the timing light, and reconnect that brown wire you un-did earlier.

Last thing is disconnect the negative battery cable for a few minutes (go grab a smoke or something to drink). This will erase the error code generated from running the motor with the brown wire disconnected. You may not have noticed it since you've been under the hood, but disconnecting that wire caused your check engine light to come on.

Good Luck, and be sure to let us know how this works out for you.

.

- Vern

 

Hey vern, you seem to chime in on every thread i look at and have a wealth of knowledge. I just posted a thread in regional. I set the timing with out using a light sunday. Car runs better than it ever has too. But i got an SES light on my way to work today. I didn't think to unplug the battery to reset the codes.

 

If it was from disconnecting the ESC wire, it should have been there from the time you turned it on today. Is that what happened? If so, reset the codes and see if it happens again.

I'd still recommend using a timing light. $20 at A/Z for a cheapie, but would still work until either the bulb burns out or you melt it against a header.... and be much more accurate than any other set timing method.

Thanks for the compliment, but there's still lots I don't know. I just try to keep quiet and lurk on those threads.....

 

nevermind, found it in tech article.