Here's a story from a reader that has a few messages for you. First, is GET THE SERVICE MANUAL!! Second is that throwing parts at a problem is not the efficient way to solve a problem, a syndrome I call the Dealer Syndrome. Third is, don't give up; Bart didn't! Use logic to try to find what the root cause of the problem is and what the conditions are which exacerbates the problem, in this case it was a simple bump in the road.
I think your idea of having a place where do it yourselfers like me can read what others have done to fix their car problems is a neat idea. I wish I had it for this one.
It all started when my brother in law called and said his 1992 Isuzu Rodeo had lost power on the Mass pike and would not go over 15 mph and kept bucking. Thanks to triple A + he had it towed 120 miles back to the Isuzu dealer he bought it from. After 4 hours of looking they called him and said they were getting no communication errors from the computer which cost 1200 dollars and did he want them to continue. Knowing that I'm always fooling around with cars he calls me and says what should he do. I said the computers are pretty reliable its usually a sensor or wire, maybe you should get a second opinion try Pep Boys maybe they can find something. The next day he calls and says he had it towed to Pep Boys and they said they were not sure what was wrong but it needed a tune-up. Then he says he has not had one since it was new and now has 89000 miles on it and can I do one for him maybe that is all it needs.
Day 3 - and here comes the Rodeo in tow at my doorstep. So its Saturday, its nice out it can't be that bad can it? We run down to the local parts store (I love doing that) and pick up plugs, wires, rotor, cap, air filter, fuel filter. We take out the plugs. A little worn but otherwise OK .we install the new ones. We check the plug wire resistance, no problem there, we install the new ones. We check the cap for cracks, not a crack to be seen. We check the rotor with a meter 0 ohms its fine but we replace them anyway. The moment of truth. It starts right up and its running like a fine Swiss clock. We drive down the street go up a hill and there it is again bucking. We turn around limp back home. Let me get the timing light out and see if that's OK. Much to my amazement the timing was dancing all over the place then no light at all then it would start all over again just before it stalled and then jump all over again. I've never seen this before it must be the computer but they hardly ever go bad do they and spending 1200 dollars to find out that's not it isn't an option yet. I thought about it for a while and thought maybe it's a loose wire somewhere .I started the engine now its running OK again I started pulling on this wire and that harness, no change. OK lets go for a ride, up to 20 mph up to 30 mph and there it goes again and I limp back to the garage .Hey, maybe there's something wrong with the distributor or electronic ignition, makes sense right?
I remove the distributor, no ignition module here but there is a clock wheel with clock pulse pick up sensor maybe the sensors borderline bad. It comes right out doesn't look to expensive lets try that.
Day 6, we call about the part but you can only buy it as one unit which includes the whole distributor for 525 dollars. Not a very good gamble, guess I'll have to keep looking.
Day 8 and a friend at work has lent me the service manual for an 1988 trooper. The wiring and electronics are almost identical. Now I'll find out what's going on, right?. I take the car out and 3 minutes later it bucks, the engine light's on and I limp back. I plug in the access code wire and a code 12 comes up. The code means the computers working OK and there are no other problems found? Has the computer lost it's mind or will I loose mine. Read on.
Day 10 after reading the manual I've decided to check some wiring. The computers + voltages check out OK. The ground side checks out OK. More about this later. All the various sensors and resistances match the book specs. The power transistor for the coil seems a little funny. Maybe it's overheating then causing the ignition to go haywire. This little bugger is hidden so well that even with the part location showing it as being under the intake manifold it's still hard to find. The parts 85 dollars, not cheap but a lot less than 1200 dollars so we order the part.
Day 12 the part's here - we put it in start the car drive down the street hit a bump and the bucking is back the engine light comes on, we limp back. It can't be the computer can it they hardly ever go bad do they? Wish I could just try one - but wait computers don't know when they're is a bump in the road at least not this one. Better keep looking.
Next day I've decided to try shaking wires again when it's running but still no luck. But what's this, I just touched the shift lever and the engine light went dim for a second. I never noticed that before. When the ignition is on but the engine is not running the engine light stays on and means only one thing, that there is power to the computer. So I get one of my kids to watch the engine light while I climb under the car and shake the transmission, it's flashing he says. I shake the drive shaft it's flashing. I shake the engine, it's flashing. I lift the car by the door handle, the light goes out I let go and it comes back on? It has to be a bad connection but I've never seen a bad connection act like this. Well I'll just have to track the wires from the computer's connector back.
The 12 volt supply looks OK and shaking the engine has no effect. The computer's ground supply wire reads 12 volts also until I shake the engine then the voltage starts jumping all over the place. Finally we've zeroed in on the problem but I've checked all ground wires in the engine compartment and non were lose? After checking this wires color code the search is on. THE CULPRIT IS FINALLY FOUND. A 10 CENT RING CONNECTOR!
On the front of the intake manifold is what looked like a large ground connector wrapped with wire harness tape and securely bolted in place but when the tape was removed it was found that there was one ground wire securely in place on one ring connector. Underneath were two more ground wires one was the computers ground wire! These were connected to another ring connector which had broken away at the connector base probably due to engine vibration but then remained partly connected because the tape was holding it in place.
Here's an explanation as to why this made the car act so crazy. When the engine was not running the tape would hold the broken connector against the good connector completing the computer's ground circuit. When the engine was running the vibration would cause the loose connector to vibrate resulting in a voltage drop to the computer. When the vibration was great enough, or a bump was hit, the voltage would drop below what it needs to work. It would then shut down or basically loss its mind (like I almost did) . But now the jack hammer like vibration of the pistons is gone causing the connector to reconnect which causes the computer to come to. Realizing something's not right it puts the engine light on and goes into fail safe mode. Fail safe mode runs the engine with fixed timing and fuel injection to bypass systems the computer thinks may have failed. But the engine doesn't run well in this mode so you guessed it, more vibration, the voltage drops, the computer quits and your bucking along it 15 mph. Finally when you stop the car and try to check for codes the only code is 12 meaning the computers OK and they're are no codes stored because the computers memory has been erased by the power loss. So if you've got a really strange intermittent problem check the grounding wires around the engine real close.
From: Bart Manhard
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