1994 Pontiac Bonneville Repair Question
Pontiac Bonneville Engine Problem
Amazing. Why are mechanics held to much higher standards than doctors? The first thing to look at is the car stalled on the side of the road. That is the most common way fuel pumps fail on GM cars, not most other brands. Your mechanic spent his time diagnosing the cause. We don't know how, but he came up with the fuel pump. He replaced it, and apparently the engine started. At this point all we could assume it was fixed and you owe him for his time, just like with any other profession.
The problem now is there are many other things that can fail intermittently and they require more in-depth diagnosis. How badly would you be complaining if the mechanic told you, "I found your fuel pump has died, . . . but I'm going to keep looking for other things and spending your money"? When you have something obvious staring you in the face, do you ignore it and keep looking?
There are sensors that commonly fail on all car brands that lead to the secondary symptom of a turned-off fuel pump. The clues there are the Check Engine light will turn on as you coast to a stop, and the engine can almost always be restarted after it cools down for an hour. Those sensors can become heat-sensitive. You didn't mention either of those things so we have to assume they didn't occur and / or you didn't mention it to the mechanic either. Even if the light went out, the diagnostic fault codes would have been stored in the Engine Computer. With no reason to suspect that, and with the engine running, there would have been no need for the mechanic to waste your dollars checking those things. He would have had your wallet in mind, and you should be grateful, not trying to rip him off.
Now that apparently the easy, relatively inexpensive, and most obvious repair was not the correct solution and has been eliminated, your mechanic is going to have to start over with the diagnosis, just like the doctors you go to who don't diagnose your ailment on the first visit. Do you demand your money back for services rendered from them?
Now, if you're dealing with a reputable shop, they should be willing to recheck their work at no charge to you. Many will even not charge you for diagnosing the same problem a second time, (something unheard of if you run back to your doctor), but you CAN be expected to pay for any needed parts. They will legitimately not remove any previously-installed parts like that fuel pump because they aren't going to try to sell a used one to the next customer. Also, if it makes it easier to take, at the mileage you listed it is not uncommon to be on your second or third replacement fuel pump already, so that future breakdown has been handled before it let you sitting in the middle of nowhere. No brand of car is immune to fuel pump failures. When my mother needed hers replaced about ten years ago, she made it well over 22 miles before it died again. Turns out the wire feeding it had rubbed through also, and removing the fuel tank disturbed the corroded spot and caused a break that the mechanic had no reason to see or look for. Just bad luck on everyone's part, but that too was a problem that was about to occur anyway and it could have happened when she wasn't so close to home.
Remember too, your mechanic is your advocate, not your adversary. He wants your car fixed as much as you do. He wants you to come back willingly for your next service, not with a complaint about his previous service.
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Sorry, forgot about your mass air flow sensor question. GM did have a lot of trouble with them in the '80s causing no-start and stalling problems, but they are much more reliable today. When they do cause problems, it is usually due to dirt and bug juice getting inside them, or there's a break in the tube between it and the throttle body. A break or gap lets air into the engine that bypasses the sensor and doesn't get measured. Dirt lowers the sensor's ability to measure that weight of the air accurately. Both conditions result in the Engine Computer not commanding enough fuel to go with the incoming air. The symptoms will be stumbling or hesitation on acceleration, and possibly hard starting. Unless that tube becomes totally disconnected, stalling is not going to occur while you're at highway speed. If the sensor did fail, the Check Engine light should have been on, and that also would set a diagnostic fault code in memory.
The problem for your mechanic with this sensor is there isn't much he can test. Based on the symptoms and fault codes, he has to replace it to see if it solves the problem. Since we typically can't return electrical parts to the auto parts store once they've been plugged in, if it doesn't solve the problem, he has to either sell it to you or remove it and set it on his shelf in hopes he will need it in the future. That's like you buying food or clothes you aren't going to use. You can't do that too much for obvious reasons.
Given the known symptoms and what has already been done, I'd start with checking for any diagnostic fault codes, and if I had to throw a dart at my decision board, I would hope it would land on the crankshaft position sensor. Most of GM's are in front of the engine where they don't get real hot, but intermittent failure is still common on all car brands. Loss of its signal will tell the Engine Computer to turn off the fuel pump.
17,655 answers provided