91 Pontiac Bonneville Timing

[allynnc]

I know there is no distributer. I have changed plugs and wires. I drive 100 miles per day. About once every 500 miles I get a stumble on acceleration. Every 1500 miles I actually get a backfire after the stumble. Then it runs great. Acts like a sticky vacuum advance, but have no idea where to look for the real problem since there is no distributer. It drives great in between stumbles and it always accelerates just fine after the stumble. Suggestions?

[richtazz]

If you have a check engine light on, pull the codes and post the findings. If there is no check engine light on, then I'd suspect a sticky egr valve.

[allynnc]

Originally Posted by richtazz

If you have a check engine light on, pull the codes and post the findings. If there is no check engine light on, then I'd suspect a sticky egr valve.

Thanks for the reply. No check engine light. This particular engine has no egr valve. I have also tried the throttle position sensor.

One other symtom of stuck timing. Sometimes when starting it acts like the timing is way off and barely turns over...almost backfiring. Hitting the starter again it starts instantly. It only does that about once a month. If I had just removed and replaced the distributer, I would guess that I had it 45 degrees off from the way it sounds when I hit the starter.

It acts like sticky timing or sticky vacuum advance, but there is no distributer and therefore I have no idea how the vacuum advance works or if it even has one.

Engine burns no oil even though I commute with 50% at 80mph interstate (44 miles) and 50% stop and go city (32 miles) per day plus another 20 miles near the house daily and makes 26 mpg in this kind of driving. It has been doing this for a year now. Naturally it won't do it when you want it to. Makes no difference whether hot or cold, premium or regular. Speed does not matter. The stumble or severe hesitation occurs after driving constant speed for 10 minutes or more. Sometimes I can go 350 miles of my normal driving without a stumble. Sometimes it will happen twice in 50.

I love the car. It has excellent power, good economy, excellent handling - better than most newer cars. It is like new inside and out...except for this stumbling.

[maxwedge]

Originally Posted by allynnc

Thanks for the reply. No check engine light. This particular engine has no egr valve. I have also tried the throttle position sensor.

One other symtom of stuck timing. Sometimes when starting it acts like the timing is way off and barely turns over...almost backfiring. Hitting the starter again it starts instantly. It only does that about once a month. If I had just removed and replaced the distributer, I would guess that I had it 45 degrees off from the way it sounds when I hit the starter.

It acts like sticky timing or sticky vacuum advance, but there is no distributer and therefore I have no idea how the vacuum advance works or if it even has one.

Engine burns no oil even though I commute with 50% at 80mph interstate (44 miles) and 50% stop and go city (32 miles) per day plus another 20 miles near the house daily and makes 26 mpg in this kind of driving. It has been doing this for a year now. Naturally it won't do it when you want it to. Makes no difference whether hot or cold, premium or regular. Speed does not matter. The stumble or severe hesitation occurs after driving constant speed for 10 minutes or more. Sometimes I can go 350 miles of my normal driving without a stumble. Sometimes it will happen twice in 50.

I love the car. It has excellent power, good economy, excellent handling - better than most newer cars. It is like new inside and out...except for this stumbling.

According to my info you have a digital egr, may not be the problem as a stumble can also be a suttle misfire, but the info regarding the egr can be found at autozone.com/repairinfo

[richtazz]

The AC-Delco part number for your EGR is 214-5004. It's a 3 solenoid electronic valve, but it's expensive, about $210. It's mounted on the drivers side of the engine, right behind the throttle body.

[allynnc]

Originally Posted by maxwedge

According to my info you have a digital egr, may not be the problem as a stumble can also be a suttle misfire, but the info regarding the egr can be found at autozone.com/repairinfo

The stumble could definitely be called a misfire as the occasional backfire would suggest. Normally when I hit the gas the car goes. Sometimes after driving any constant speed from 20 to 80 the delay can be 1-2 seconds of sputtering and potenitally a backfire before it suddenly takes off like normal. It acts just like the timing is grossly off, but only occasionally. Taking it to a shop costs hundreds and they cannot duplicate the problem. Most people with my income would be driving a new expensive car, but I just don't believe in wasting money and like the Bonneville just fine. I tried a new Impala and was extremely disappointed in comparison, didn't have the handling of my Bonneville. It felt lightweight and cheap. I can afford the fix if I can find it and plan on driving it at least another 100K.

[BIGTYMEHUNTER]

It may also be a cam sensor going bad which tells the ecu at what point to advance and decrease ignition timeing

[richtazz]

good suggestion Big, but normally a bad cam sensor will trip a code. I say normally because it doesn't always, so if teh EGR checks out, that would be the next thing I'd check.

[allynnc]

Result. Bad coil. Idled fine, ran fine. Under heavy load the hot spark from one point on coil was jumping to the weak point on the coil and getting two cylinders trying to fire at the same time...backfire.

[GTRider0]

I had a 93 bonneville and everything went on my my timing started to go wrong and there is no way to get that fixed because it is all electronical and controled by a computer and then my lights wouldn't work radio door locks i would sugest looking for a new car and waiting till this one just craps out on you thats what i did good luck hope i helped