'86 Bonneville Throttle Problems - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 10-31-2007, 11:41 PM   #1
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Default '86 Bonneville Throttle Problems

Hey guys, new to the boards. I've got a dilemma!

Someone recently gave me an 86 Bonneville. It'* one of the 4.3 liter models, and apparently rare, because it'* fuel-injected, and not carb. I'm wanting to fix it up into basically a new car, and it'* in great shape as it is, but I have one small problem.
For some reason, it doesn't idle correctly, and when running, it has a tendency to cut off. It'* like theres a spot in acceleration where it just bogs down. Trying to get away from a stop sign is also difficult. If it were a carb vehicle I would assume the carb needed a rebuild or something, but it'* fuel injected.
A mechanic I know was under the impression that the throttle body was bad. I didn't think that was it, but I went ahead and got one off a junker, cleaned it up and put 'er on.
Nothing.
So I started changing sensors. I've replaced the map sensor, the oxygen sensor, the air idle sensor, the thermal sensor that sits in coolant on the front of the engine, I've replaced all but one. It'* one that has been discontinued called a EGR control valve relay solenoid. I have tried every auto parts store in the town (advance, O'reilleys, napa, autozone, pontiac dealership) looking for it.
The only reason I know it exists is because I also replaced the EGR valve, and the heat sensor which connects to it. The Pontiac dealership I went to for help not only couldn't tell me what the part was called, but insisted there was no such thing as a fuel injected 86. I had to convince the mechanic on duty to actually check the computer, at which point he admitted he was wrong. Finding the part amounted to letting me look at an exploded diagram of the engine and identifying it by sight.
So after all this, the problem really hasn't changed. I have discovered it will idle correctly if warms up enough, but there'* still a spot in acceleration where it wants to die.
Most mechanics I talk to tend to believe the car doesn't exist or else are reluctant to work on it. The Pontiac mechanics couldn't give me any advice either. I'm sort of at my wits end at moment and quite honestly debating scrapping the whole thing and gluing a carb on it.
Anyway, has anyone heard of a fuel-injected 86? Does anyone have any ideas where the problem might lie?

Thanks in advance......
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Old 11-01-2007, 12:36 AM   #2
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If you're fuel injected, you almost certainly have a TPS. I'm not familiar with your setup, but I've had other TPS equipped GM cars in the past (3 in the last 15 years or so) that developed 'dead spots' and were (in all 3 cases) bad TPS'*. Throttle Position Sensor. Should be installed on the throttle body on the opposite end of the throttle shaft from the cable.
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Old 11-01-2007, 11:38 AM   #3
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That'* one of the first sensors I replaced when I changed out throttle bodies. On my model it looks something like this:



It had no noticeable effect on the car'* performance. You think it'* possible the harness it plugs into could be bad or have a short?
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Old 11-01-2007, 12:16 PM   #4
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Snap a Picture of the engine if you would...

Back in the day or at least 86 this car should have either come with the 3.8, or 5.0( Chevy 305 )

If it has a Chevy 4.3, chances are it not the original Motor


But just for **** and giggles... Post the 1st 8 characters of the Vin for me

This will give me more ideas as to what direction to go in

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Old 11-01-2007, 09:32 PM   #5
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I'll throw up some pictures and the vin numbers sometime before Monday. I'm keeping it parked at a friend'* garage...

It'* definitely factory. I don't know what makes it so special, but there aren't many of them. People refuse to believe it exists until they pull it up on a computer.
The Haynes repair manual for 70-05 lists it, as well as the Pontiac dealership'* computers, and all the auto parts store'* computers.
It'* just that no one'* actually ever seen or heard of it.

I'm not sure how reliable he was, but one mechanic told me that this particular engine was used in some GMC pickups around the same time period. Like I said, I don't know if that'* true or not...

Also, as of today, every sensor has been replaced save for the solenoid we couldn't find that runs the EGR valve. As things are, I don't think it'* bad. The vacuum line is working, and checking voltage on it proves it'* getting power. Also, All the fuses have been checked.

In other news, I finally found a nice 60/40 seat cover. Now if I could just get the car running right.
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Old 11-02-2007, 11:08 AM   #6
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Yes that would be the first one I have heard of... GM always did have some odd balls here and there.. lol

But that 4.3 makes it interesting

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Old 11-02-2007, 11:21 AM   #7
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Have you checked the ground to the engine? I know that frequently enough in these sensor based engines..a bad or questionable ground can cause serious sensor issues. Battery connections being clean might be another possibility.

Another item would be fuel pressure. Maybe your initial start off is pulling enough from the pump that it can't keep up for that bit.
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Old 11-05-2007, 01:23 PM   #8
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Well, I wasn't able to tinker with the Bonny this weekend- I had other commitments. So I don't have any pictures yet. Though, whether it gets fixed or not, I'll have some soon.

However, we managed to get ahold of a computer key and it was hooked up and checked this weekend. The resulting code corresponds to "electronic spark control". If I'm right that is a large electrical connector on the left side that looks something like this?:



Anyone know for sure? My repair manual says nothing about the thing.
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Old 11-05-2007, 04:47 PM   #9
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That may be plugged into the Spark control unit on the firewall or there could be a possibility the Module( if it has one ) inside the distributor is going bad... Forgive me as I haven't seen a RWD GM for a long time

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Old 11-05-2007, 10:54 PM   #10
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I got around to the garage this evening to find the ESC. It was where I thought it was, but I don't think it'* the real problem.


This connector underneath which runs through the same wiring harness and uses the same fuse is for some reason almost melted on the inside. I'm going to try to find a junker tomorrow and get the whole harness (ESC, this piece, and the fuse), and see what happens. Just for the experience, I tried just disconnecting both, but the car wont start without them attached. Hopefully this is THEE problem.
Here'* a couple more shots...


With the hood up and the breather off. There'* no real rust, just some spots where it'* losing paint. As soon as it runs correctly we're going to paint it as well. Probably a deep blue with some flecks/sparkle to it.
I'm also set on getting some new rims. Nothing Terribly fancy, and certainly no spinners. Just something with a little more class.


Here'* the best I could do trying to get a shot of the engine.


Here'* the new throttle body and the injectors. The injectors work, but I'll probably replace them sometime down the road. The car'* been sitting a couple months and I think the old gas probably hasn't been good for it. We drained what we could before we put it back on the road, and ran some cleaner when we filled up the tank.


Here it is again with some of the new sensors. The throttle position sensor is in the middle of the picture. Wires run from it to the new map sensor.


Part of the interior. It'* in great shape. I was incredibly surprised the dash hadn't split or cracked. All the control panels and the wood grain faceplates are in good shape. For now I'm going to cover the seats, but I may replace or else re-upholster them in the future. The front ones are well-worn with a split or two, but the back are more or less unused.

Also, as promised, the first 8 of the VIN:
262GN692


I really appreciate the help you guys have offered with this thing.
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