This does NOT seem right(re: my '88 Riviers'a miss problem.)

[rca2000]

If youn recall.. I have been keeping you all informed of the progress I am making with my "new old" car--the 1988 Buick Riviera I bought a couple of weeks ago. It had a persistent, but intermittent miss in one cylinder. Plugs and wires did NOT help, and so I gave up, and had it diagnosed Wednesday. The #1 injector was NOT firing all of the time, and the shop thought the PCM was at fault. However..they did NOT have time to replace it. So, I took it home, and it did the "miss/no-miss thing.. I didn't go anywhere much Thursday, and Yesterday...I drove the car, it had it's usual problem.

Today, however, in between digging the blower resistor out of my mom's Malibu, I was going to get a new one, and was wanting to take my car. However--I wanted to try and remove the PCM and try and fix it.

However..(and I STILL don't really know why I did this.) I decided to do the "easy thing first", and check out if there was any connectors from the injector harnes that just MAY be the problem. I found the connector near the back of the PS Pump and alternator. It has 6 or 7wires and plugged into another plug, that led to a big wiring harness.

I pulled the "lock" out of the connector and it broke. SO..I removed it from the plug, and pushed the plug back and forth a few times, and them made sure it was tight. I then went back to see how hard getting to the engine computer is(and it is VERY hard to get at..harder than the blower resistor in my mothers car. )

However..the car was running and it felt like it was NOT missing..I put it in gear, and it did NOT mioss. SO..I drove it to Auto Zone to get the new resistor. It ran fine all the way there...and back. stops..No miss!!

Later tonight..I restarted it...no missing...I went to Krogers to get some gas...STILL no miss.. I decided to go on a "little drive" since it was runing VERY well, and smoothly. I reset the mileage calculator and drove about 25 miles altogether..about 60% highway, the other "in town..not ONE miss all of that time. It has GOOD power, and runs nicely in overdrive in 4th gear lockup.I was getting over 26 MPG average on the highway, and about 23 overall. When I parked the car..it was still running fine. I even gave it an "italian tune-up" just before going home. It accellerated from about 25 to 70 or so QUICKLY, and smoothly, with NO miss or stumbles!!

So...I wonder ..is THIS the problem I have had all along?? What is the chance that the connector is(was) causing the miss..and I have fixed it(for now..anyway...). Or..was this just "dumb luck" that it ran fine EVERY time I restarted it after messing with the connector??This is the LONGEST it has gone without missing since it started to miss. 5 stops altogether and restarts..no miss ANY of those times!!

What are the odds,....that the problem was that connector....and NOT the PCM?? And should I get some "de-ox-it" and clean up that connector, to insure it will not "mess up" again??

 

[Eric H]

It could very well be that was the problem. I believe this uses sequential injection, i.e. each injector is fired individually by the PCM rather than 3 at a time in the non-sequential system.
There is one B+ wire to the all injectors and 6 grounds controlled by the PCM, if one is dirty or otherwise not making a good connection it could cause an intermittent misfire on a single cylinder.

OTOH GM had plenty of problems with the PCM's during that period, these usually show up as intermittents and can often be induced by rapping on the PCM with a screwdriver handle while the engine is running and observing any glitches in the way it runs.

 

[devoid]

You do know about Deoxit, right?

 

[blue_lateral]

It's never the PCM. I have seen bad PCM's, but for every bad PCM I have seen, I have probably seen 50 or more cars where someone hung a new PCM on the harness, and the car was still broken. It may be that it's easy to look back with 20-20 hindsight and say that, but if I had to bet on either the PCM or the wiring, I'll pick the wiring every time.

By the way, these things are *not* usually easy to figure out, especially when they are intermittent. It's quite probable he was not trying to scam you, even if it turns out he was wrong.

John

 

[Pioneer727]

On a car of that age you should clean all connectors they do become dirty and can cause all kinds of problems did all the one's on my 87 Jeep Cherokee Chief.

Ron

 

[Tony V]

John, i hate to disagree with you but it CAN be the pcm in these with this problem. Of course before replacing the pcm in the ones i repaired, i did check the harness and connectors before hand and did clean them if they seemed suspect. The ones that ended up being the pcm i actually pulled a couple apart and saw where resistors had overheated in the area where the injector pulse signals are produced and they actually burned the board. So never rule out the pcm although most will check the obvious first before replacing it. After beating my head against the wall with the first one i had this problem with i learned to start with the check of the injectors and work my way back to the pcm. One good thing about GM's compared to Ford or Chrysler is that the color code at the injector is the same all the way to the pcm so finding a fault although difficult with a wire is easier to find with GM's compared to the others. I do agree with you that the pcm is last on the list to check though. It appears the garage that Jack took his to didnt go through this procedure when checking it out. If they were too busy to change out the PCM i'm sure they didnt spend alot of time checking it out. Concidering how they route these harness' anymore i'm surprised that half of them dont melt.


Jack, it sounds like you lucked out buddy on yours and hope this was your problem. Just clean the connector up good and use a zip strap to hold it together afterwards since the fastner broke on ya. I have used a very light coat of white lithium grease in the past on a few of them with chronic corrosion problems at the connectors as a preventive measure but only if its a repeat problem. Hope your luck continues!
-Tony

 

[blue_lateral]

Tony- I don't really disagree with you at all. It's just that you have to really check the circuitry all the way back to the PCM, and hardly anyone does. I've fixed a lot more wiring harnesses than PCM's

Jack- I think you've nailed it. :thmbsp:

John

 

[madpioneer]

Not really surprised to hear a that a conncector was the trouble. When I bought my 85 Vette it ran like crap till it warmed up. Every time I started it. If you started it cold and gunned the engine it would sputter and backfire badly till it reached operating temperture. This went on for awhile till I could get funds for parts. After doing a tune up and doing various things in the engine compartment I found a dis-connected wire? Reconnected it to its proper mate and solved the problem. Was to the idle air mixture motor. Could not believe that one connection could have such a massive effect on the way the engine ran. :headscrat