2000 Bonneville starting problems. Help
 

Just picked up a 2000 Bonneville. Started up just fine, shut it off, and then decided to start it up again right away and it didn't want to start. It was acting like it wanted to hit, but just wouldn't. After a few tries it finally started. General concensus was I shut if off while it was still on high idle and was just loaded up as you could smell a little fuel. Drove it home and it ran great. Stopped to get gas, no problem. Next morning it started just fine. Pulled it back to the garage to do a couple things to it. Went into town, came back, changed oil, air filter, just general maintenance stuff. Won't start. Doing the same thing. It acts like it wants to, but won't. Went to my dad's house to pick up his fuel pressure tester, came back (10 minutes) hooked up the tester, made a dumb mistake and instead of just turning the key on to read the gage, I hit the starter...and it started. Tried 3 or 4 more times periodically after that and it started every time. But I'm a little gun shy now. Any ideas??

Leave the gauge on,start it up and let it run the same as before. Shut off and see how quickly the gauge drops off and what your reading is after 1/2 hour. If it drops to 0 -10psi see how quickly it goes up to 50-55 (what ever the spec is) WITH just turning the key on. You could have either a injector leaking into the cylinders or a faulty pump check valve that's not holding the pressure forward.

To take the above to the next step. If it holds pressure, the fuel system has integrity. (regulator, injectors and fuel pump are good). If the pressure drops to near zero, you have an issue. You can use shutoff valves in the feed and return lines to isolate. Shut off return valve to the tank. If pressure still drops, leaking injector, (s) . Much more common issue is failing crank sensor. They fail in an intermittent mode all the time. Do a quick check for ignition, next time it won't start. Also, next time it won't start, hold the pedal WOT and see if it starts. That would indicate a leaking injector as well. 3800's are pretty easy to deal with for the most part. Take care.

Go over to Pontiacbonneville.com, join, and describe your problem. There's a million buys there who can help.


I would also suspect the security system. An easy fix, but annoying,

"Much more common issue is failing crank sensor."

Quick check on a crank sensor would be if car has a tach see if the needle is moving while cranking or scan tool show any rpm while cranking.

It’d be interesting when it doesn’t start to hold the throttle wide open and see if it starts (treating it like it’s flooded). Some models seem to flood when started cold a couple times and not run for a bit.

The other suggestions are great.

I've had one before with a bad crank sensor. This one acts a little differently than my other one did. My other would just act like the ignition is turned off when cranking. This one acts like it's trying to fire but won't.

The fuel pressure with it running was at 45 psi. I think they are supposed to be 45-50??

That is a great "quick and dirty check". No tach wiggle or 75-150 RPM on the scan tool, you have your answer.

See what the pressure does when you key off? If you determine the injectors are a problem, pull them out and get them to me. I can ultra-sonic clean them and flow test them. I would need them for a week if you can be without.

Started the car several times today. No problem. Put the fuel pressure gauge on it and it was between 45 -50. Left it on for 45 minutes and it was at 32. Is that an issue?

I would say that test is slightly inconclusive. Probably not an issue. I would move in the direction of verifying the ignition is functioning when it won't start. Is there a chance this model has the trouble prone Motorola ignition? Or is it the Delco system with the 3 separate coils?

I don't know. I didn't pay any attention to that Mike. I'll look tomorrow and get back to you.
I've driven it to a few diferent places today, started it about 8 or 9 times and haven't had any issues.
Thanks.

32 is low, I don't work on many GM but does the car have a vacuum operated fuel pressure regulator up on the rail? If so unplug while running and see if that 32psi goes up. Also see if fuel is coming out that nipple,had one that was leaking though the diaphragm causing rich mixture screwing up the o2 sensor.

To be clear, the 32 was after I shut the car off. Was watching it to see if it leaked down fast or what would happen. After 10 minutes it was still close to 45. Then I got sidetracked doing other things and came back to it at 45 minutes. For all I know that leakage could have been in the gauge. With the key on it's always been at 45 to 50. And yes, it does have a vacuum operated regulator.

My '99 Bonneville had the Delco coils.

I gave the wrong address for the club. Here it is. http://www.pontiacbonnevilleclub.com/. Lots of good info here.

45-50 pounds while running is perfect.

So I drove it to work today and just went to lunch. On my way to town the "Service Security System" alarm came on. I've made 2 stops since then and it has restarted every time without hesitation, but the alarm makes me wonder if that isn't the issue. I knew of an Oldsmobile that had starting issues and it was found that there were some corroded or broken wires going to the anti-theft system causing the problem.

Yeah. The wires are tiny and frequently break.


What you need to do is use an ohm meter to "read" the key to see what the reading is. Next, your order the resistor (I got mine at Radio Shack, RIP) and they were 5 for a dollar. I'm sure amazon has them.


You just wire the resistor into the circuit before the key and that solves the problem. I've had 2 Bonnies, a '99 and '97, and they both eventually failed and required this fix.



If you got over to pontiacbonnevilleclub.com and search the archives, this fix will pop up, and it's an easy fix.

Thank you.

To add to the security system issues. It is very possible that is causing your problems. The tiny wires are under the steering column. Green, yellow, white, I think. They are like 24 gauge, very small. You can bypass the system by supplying the correct resistance to the module and bypassing the key chip as mentioned above. Pretty easy. There are several Youtube videos showing how to do it. I have done half a dozen over the years.

Old thread, new problem. Car was running rough and even died a few times. Put a scanner on it and it said Mass Air Flow Sensor. So I replaced it. Now it runs down the road ok, but idles rough. Doesn't die but will act like it's going to and the idle will fluctuate from 600 to 1100. Scanner just says idle rpm unusually high detected. But doesn't say why. Any ideas?

Remove and clean the throttle body thoroughly, paying special attention to the throttle blade. And make sure you have no leaks in vacuum hoses.

If your model has the PVC valve in a pocket in the plastic intake manifold? If it does, carefully turn the plastic cap that holds it in and remove the PCV valve and check the O-ring that goes around it. Those were problem areas for vacuum leaks. Also if this model has the plastic intake manifold they were famous for a melt through where the EGR tube sends the exhaust gas back into the intake near the throttle body. Famous for water leaks, vacuum leaks and other chaos where the pipe attaches. Dorman sells an improved replacement intake. Finally, the EGR valve could be sticking slightly open, another common problem. Check the pintle position with a scan tool. Should be 0 +_ 2% at idle. Desired vs actual position should track +- 2%. It's always possible the "new MAF" sensor is defective. Should pass 6-8 grams per sec at a hot curb idle. Hope this helps.

Thanks guys. Gives me at least some direction. I would love to just stick a Q-jet on this and be done. lol

"Also if this model has the plastic intake manifold they were famous for a melt through where the EGR tube sends the exhaust gas back into the intake near the throttle body."


If this were so, it would be eating coolant like crazy.


There are aftermarket intake manifolds where they are "sleeved" with metal to prevent this. They run around $125, and it's an easy swap, too.

Check and see where the IAC, Idle Air Control number is at idle. This is the bypass when the throttle is closed. It should be around 10. If it is at zero, then you have a vacuum leak. At 0 it is all the way closed and if it is still running, then air is getting in somewhere else.

Mike, you were right. I just went and purchased another MAF sensor and now it's running fine. It's sad that you can't always trust new parts. Thanks.

Glad you have it running good again! Couple little things I always try to remember from my mentor, James Halderman. You may remember him from Sinclair College and he is the author of dozens of automotive textbooks. 1. "New doesn't mean good", (just means it is clean and in a box) 2. "When in doubt, take it out". This means the computer has a back-up system for most of the sensors. If you think a sensor is defective, un-plug it and try to drive the car. If it runs better without that sensor, the problem is the sensor. It's a good test for O2 sensors, MAP, TPS, IAT, ECT.

The Dorman replacement intakes were pretty good for a long time, then went to hell. The last one I did (for my 99 bonneville), was so malformed inside that I used a heat gun and wood scraps to "re-form" the damn thing to where it would fit. It was a train wreck. I was just gonna order another and then I heard from someone that they were ALL bad.

I made my own. Took another dead manifold, drilled the hole out to 7/8" and sleeved it with 7/8" stainless steel tubing and fixed it in place with JB weld. Held for 90K and was still OK when I sold the car.