Hi guys....been sorta stumped on this one.

1990 automatic C4 coupe
see signature of mods list

Has developed a skip/miss that is most pronounced when at idle but definitely remains at all RPM levels.

So far this is what I have done.

Checked and replaced Plugs
Checked one by one wires.....(replaced out each one at a time, tested for skip/miss....skip/miss still present....conclusion...not the wires.
Changed out Rotor, Cap, and Upper Coil
Checked at night for any kind of sparks in the engine compartment....none
Changed out Throttle Position Sensor

so far none of these have cured the problem

Today I was going to remove the Throttle Body and clean the IAC (BUT....I just did this about a month ago?...so I dunno) Not so confident this would be the problem....since it is not just the Idle doing it.
HOWEVER....iam not sure if I installed it correctly back in....something I heard about a correct IAC resetting procedure....please if anybody knows how to do for a 1990....let me know.

I have not replaced the Ignition Module yet (but this was replaced about 4 months ago) so again....Iam not sure if that could be a factor...

The car besides feeling like it has a mild cam in it (that lopey feeling) drives and performs no different then before.

How bout the knock sensor? Iam not sure if that would throw a code or not....or cause this type of problem

suggestions welcome...

 

Can you hook up a data logger and get the numbers? It's all about the numbers. Does the RPM change in concert with the miss?

Malfunctioning 02; I just walked that road a week or so ago.

I don't think knock sensor won't throw a code unless it or the ESC has failed. The ECM tests the KS each time the engine is started and if it fails, you'll get a code. Otherwise all it'll do is cause the ECM pull out timing when knock is detected.

I'll check the manual on that one and see what else GM says to look for.

Did you install a coil with the correct wire colors? Good connection of the ground wire?

Did you check for a vacuum leak using the old garden-hose water method.

Did you check the resistance of the injectors and plug wires?

Jake

 

Iam gonna try to get some EASE software or at least the cable...my brothers got something on his computer that diagnoses the car....not sure if its any good or not....but willing to try....

Yep I installed 2 different coils...wires correct color....no difference, problem remains.

I did not check for vacuum leak....what are you referring to by saying old garden hose check? Iam not aware of this tip..lol

I still have to check the resistance of the injectors... what does your manual say...can't seem to located now the correct ohms they are suppose to read....12 maybe?

Might be time for Ford SVO replacements. I mean at $99 who can pass that up....by the way....anybody know if those just go right in without modification? I know about lowering the fuel pressure.....Iam talking bout the clips....I have read something about them being different?


Thanks
Jeff

 

Could it be bad,old gas? Water in the fuel? I once chased a miss for about 400 miles. Next fill up it went away. Just a thought.

 

replace the fuel filter. My 89 did the same thing, I replaced all kinds of parts. It was the fuel filter all along

 

well Iam about to go and filler up....so we will see...

I just changed the Fuel Filter like 1000 miles ago...sorry I forgot to mention that one.

Oh yeh, I did put on a AFPR....and its set to almost stock.... 38.5 was stock I have it at 40....so no biggie there.

 

The garden hose trick is to pour water around all the sealing areas with the engine running and watch for a change in idle, white smoke out the exhaust (when the water gets sucked into an intake port and turns to steam).

Some use carb cleaner, an unlit propane torch, etc. I just use water.

The injectors should all check with 16 ohms minimum. I checked an old set I have that worked fine in m 355 when I was running that engine. Each checked 16 to 16.5 ohms, so they may not all hit 16 ohms on the head, but if one or more is/are bad, you'll see a noticable difference in the reading.

I didn't get a chance to look in my Shop Manual for other GM tips and clues since I'm dealing with my Anti-Lock dash light. I'll try to get to that today.

I wouldn't be too quick to jump in a buy new injectors. You wouldn't be the first guy to do that and not solve the problem. To me, throwing parts at the problem isn't the way to go about it. You could end up spending a lot of money needlessly and still have the same problem.

Just like at the doctor, diagnose then treat.

Jake

 

add fuel system cleaner.... Techron then fuel filter... AS a service

 

Check your oxy sensor.

 

Accel injectors did that on my car. Yep, got a new set of injectors, Accel, and runs like new.

 

Here take a look and see if you can pick out whats wrong....

Fuel Injectors:
Drivers side
#1: 17.3 ohms
#2: 17.4 ohms
#3: 17.2 ohms
#4: 17.4 ohms
Passanger side
#5: 17.3 ohms
#6: 8.9 ohms
#7: 17.3 ohms
#8: 17.4 ohms

When resistance is that low what does that mean? The injector is partially clogged? Is not working at all and Iam running on 7 cylinders?
or is broken altogether?

hmmmmmm....I am thinking a change is in order for in the springtime seeing how I only really have less then a month to drive it here now in New England.

Running the car like this won't hurt anything will it?
I put in some of that injector cleaner to see if it might free up...I doubt it, but worth the $2 I spent.

Also in the spring when I do them all what do you guys recommend to go with....Iam looking for a cheap but effective alternative....I have heard much about the ford SVO injectors...something about they are like 100 a set....whats the deal with them? do they go right in or do you have to mess with them...I think I read somewhere about the clips being different or something....

 

ttt

 

6 is the problem - coil is shot and the injector needs to be replaced - you might want to replace all of them, though you don't have to.