86 GN cuts out and miss at light throttle

[timdesu2000]

Hey all. I have been searching a gremlin for some time now and I am just about to the point I don't want to drive the car.
I am fighting a light throttle cut out condition. At times almost feels like a miss but today it was the worst yet. Could even feel it cut out while coasting.
So far I have replaced the Ign module with a new delco. New coil. Rechecked plugs and wire. Added an ignition hot wire kit. Swapped ECMs. Checked and rechecked grounds. Added an extra ground to the coil bracket. Swapped out proms. Tap tested the MAF. New delco crank sensor. Checked the crank bolt. Checked voltages at the ecm while the car was acting up. Ran a new circuit from the ecm to the ign coil for the est circuit and the bypass circuit.
Here is what I found out today. If I put it in back up spark and fuel mode it quit cutting out so it seems to be an input to the ECM causing this. Also the MAF needed to be less than 40 grams of slow. After 40 it will run fine. Wide open is fine. Will do it in any gear but when the tcc is locked up it will jerk you badly. Its done it at various TPS voltages. I have swept the TPS with a volt meter and didn't see any drop outs. It seems when it acts up the o2 voltages will drop way down lean. Almost like all fuel is cut off for a second. I am leaning towards a MAF sensor dropping out.
Guys tell me your thoughts. IF it does lean towards a MAF would I be better with a translator and LS1 sensor?
Thanks,
Tim

 

[TurboTGuy]

Be sure to contact "turbo89".

He will tell you to return you car to "absolutely pure stock" to avoid the EPA...............

Oh, and the sky is falling, too.

 

[Nick Micale]

........ Almost like all fuel is cut off for a second. I am leaning towards a MAF sensor dropping out.
Guys tell me your thoughts. IF it does lean towards a MAF would I be better with a translator and LS1 sensor?
Thanks,
Tim

My thought is you have gone over your electrical system to find the issue, but have you checked your fuel system?

A simple test is to hook up a fuel pressure gauge which is visible when driving to verify ample fuel delivery.

I have cured a few GN's with a similar issue by just raising the base fuel pressure, sometimes as much as 10 psi?

 

[gunzandgearz]

Another thing you might check is the injectors being plugged as this could be causing your issue.The injectors can have trash or a lot of carbon buildup and not flow worth a dang at idle but when you give it throttle the fuel pressure will rise and overcome the flow restriction in the injectors.Try putting in a fuel cleaner in the tank and use the bg 44k as this is the best stuff on the market bar none, problem is you can not buy this from any auto parts store as they only sell to auto repair shops,but look around and see if any shops carry this product in your area and see if they will sell you a can of it. Also look at your fuel trims at idle, if your lean at idle and not at cruising speed this may be your problem.As far as the maf I doubt that is it because its doubtful that it will meter airflow everywhere except idle.

 

[TT/Ameasap]

sounds like a tip in stumble? What injectors and what chip?

 

[VtheGNMan]

I had a similar stumble last year when cruising but not when accelerating just like your description. I swept thru the TPS with car off and never saw a drop off either. I would drive it with the SM turned to the TPS voltage because I just had a feeling. Finally I caught it dropping off. Replaced and cured problem. I don't condone throwing parts at a car but it could be the ECM is getting a drop off signal and the refresh rate just isn't showing or catching it. A logger would catch it.

 

[TurboBuRick]

Pull the cam sensor cap and check the wheel for play. Grab the wheel and try to turn it right and left. Also pull up and push down. Any kind of play will translate into driveability issues. Especially down low.

Rick

 

[timdesu2000]

I did a BG fuel service on it a few hundred miles ago. Also added the 44k to the tank. I have the fuel pressure set at 43 psi with the vacuum hose off per the turbo tweak chip. Its not a tip in stumble. More of a steady state cruise cut out. I have thought TPS many times but its not at the same TPS voltage each time it happens. It will do it from .60ish range up to about 1.0 volts.
I have not checked the wheel in the cam sensor. If it has play I am guessing the whole shaft and sensor assembly will need replacement? It about has to be an input to the ECM as it quits bucking and cutting out if put in back up spark and fuel mode.
I can try to up the fuel pressure and see if it helps. If so then I could have an injector giving me fits but it feels like the whole engine cuts out not a single cylinder misfire.
Thanks for your ideas. Keep them coming and I will check these few things in the next few days and post back.
Tim

 

[Linewalker]

When mine was doing this, I pulled the ecm and found that water had gotten to it and corroded the pins. I used steel wool to clean the corrosion and then put some dielectric grease on them. The problem went away. Just another thing to check.

 

[gunzandgearz]

Have you done a tap test on the ecm like you did with the maf, you might try this to.Also if you have only endplay with the cam sensor and not side to side play you can drive out roll pin and shim it.Also does it do it every time you drive it or only when hot, any certain gear, need info for diagnostic help.

 

[VtheGNMan]

I couldn't find a single dead spot in the TPS either. It would also do it sometimes and not others. Drive it with the TPS up on the SM display. It took me a while to finally catch it on the display. I was thinking it was like the torque converter locking and unlocking but it was more like a cut out or surge than just a change in rpms.

 

[timdesu2000]

I have tap tested the ecm and also swapped ecm's. It was usually after warm up but when I drove it 2 days ago it did with in 1 minute of starting it and continued for the 23 mile trip to work. Doesn't have any difference on what gear its in. Actually did it when I backed in to the garage when I got home. I cam put my DVOM on the tps and do a min max record to see of I can catch any drop out. Its more violent than the torque convertor locking and unlocking.
I have checked the ecm terminals and even did a tension drag test. This issue has been going on for a couple years now and 2 days ago it was the worse its ever been. As stated earlier it was even cutting out on a coast at 40 mph.
I haven't had a chance to pull the cam sensor cover off yet but I am heading there next.
I have also checked the fuse links and tugged and cant get them to separate so they seem to be intact.
Keep the info coming and thanks again for the suggestions.
Tim

 

[GNRick]

If you still have the factory MAF you should upgrade to a MAF/translator anyways. Plus it might cure your problem. LT1 MAF works fine on my car.

 

[gunzandgearz]

I have tap tested the ecm and also swapped ecm's. It was usually after warm up but when I drove it 2 days ago it did with in 1 minute of starting it and continued for the 23 mile trip to work. Doesn't have any difference on what gear its in. Actually did it when I backed in to the garage when I got home. I cam put my DVOM on the tps and do a min max record to see of I can catch any drop out. Its more violent than the torque convertor locking and unlocking.
I have checked the ecm terminals and even did a tension drag test. This issue has been going on for a couple years now and 2 days ago it was the worse its ever been. As stated earlier it was even cutting out on a coast at 40 mph.
I haven't had a chance to pull the cam sensor cover off yet but I am heading there next.
I have also checked the fuse links and tugged and cant get them to separate so they seem to be intact.
Keep the info coming and thanks again for the suggestions.
Tim

Yep you've definitely got a wild driveability issue.Try to wiggle test all of your wiring by the sensors especially the ones that control air or fuel (ie cam sensor maf tps) to see if it will act up with no load on engine in driveway. If non of this works this is where I break out my scope and start eyeballing all of the sensors electrically to see if I can catch any of them dropping out or any weird signals, problem is most people don't have a 2 or 4 channel scope to check this stuff with.Your meter might catch the tps or another sensor dropping out if it has a good quick sample rate like a fluke,its worth a shot.im beginning to wonder if computer or chip is bad. One more thing is trying to use a heat gun to get the sensors hot to see if that is an issue as sometimes this works, also,see if a friend or buick guy in your area will let you swap out with their computer to see if anything changes, your on the right track as most people don't even know how to drag test connectors or spaids good luck and report back.

 

[timdesu2000]

I have a 2 channel scope. I can watch for any glitches but I don't have a good signal to compare it with on something this old. I can give it a go. The problem has been it usually wont act up on just a stall test. Tuesday was the first time it has done it this bad and at low rpms and speed. I just didn't have time right then to start testing. I do have a fluke with 100ms record on it. Same issue with the original ecm and also an AC delco reman. Also the factory prom and my turbo tweak prom. I have wondered about the calpac but I don't have a spare. I am leaning towards the cam sensor signal being erratic or the MAF dropping out at low flow. I will have to bring my scope home from work.
Thanks all and keep the ideas coming.

 

[gunzandgearz]

Ill tell you one other thing to try that has also worked for me when cars have come into my shop with driveability issues like this and they are intermittent like this I will hook my meter to the pcm wiring and check all of the power and grounds coming into and out of the pcm, one at a time while driving the car and when it screws up see if you still have your 12 volts or 5 volts or grounds,, I have found a lot of issues this way because when the computer glitches out or the sensor drops it will show on the meter.You do need a wiring schematic though to know what your looking at.

 

[turbo89]

I have a 2 channel scope. I can watch for any glitches but I don't have a good signal to compare it with on something this old. I can give it a go. The problem has been it usually wont act up on just a stall test. Tuesday was the first time it has done it this bad and at low rpms and speed. I just didn't have time right then to start testing. I do have a fluke with 100ms record on it. Same issue with the original ecm and also an AC delco reman. Also the factory prom and my turbo tweak prom. I have wondered about the calpac but I don't have a spare. I am leaning towards the cam sensor signal being erratic or the MAF dropping out at low flow. I will have to bring my scope home from work.
Thanks all and keep the ideas coming.

one thing at a time .. if you suspect the cam sensor .. with the car running disconnect it and then drive it .. if it goes away you know what it is.

If I was to bet ... either MAF or throttlebody ...

Maf is far more frequent so I would follow up the cam sensor diagnoses with putting in a known good maf .. anyone near you that you can borrow a MAF ... make sure its a ACDELCO non reman unit .. the reman stuff is junk.

 

[David Husek]

Hey all. I have been searching a gremlin for some time now and I am just about to the point I don't want to drive the car.
I am fighting a light throttle cut out condition. At times almost feels like a miss but today it was the worst yet. Could even feel it cut out while coasting.
So far I have replaced the Ign module with a new delco. New coil. Rechecked plugs and wire. Added an ignition hot wire kit. Swapped ECMs. Checked and rechecked grounds. Added an extra ground to the coil bracket. Swapped out proms. Tap tested the MAF. New delco crank sensor. Checked the crank bolt. Checked voltages at the ecm while the car was acting up. Ran a new circuit from the ecm to the ign coil for the est circuit and the bypass circuit.
Here is what I found out today. If I put it in back up spark and fuel mode it quit cutting out so it seems to be an input to the ECM causing this. Also the MAF needed to be less than 40 grams of slow. After 40 it will run fine. Wide open is fine. Will do it in any gear but when the tcc is locked up it will jerk you badly. Its done it at various TPS voltages. I have swept the TPS with a volt meter and didn't see any drop outs. It seems when it acts up the o2 voltages will drop way down lean. Almost like all fuel is cut off for a second. I am leaning towards a MAF sensor dropping out.
Guys tell me your thoughts. IF it does lean towards a MAF would I be better with a translator and LS1 sensor?
Thanks,
Tim

Disconnect the cam sensor after starting engine and see if problem disappears. If so, check condition of the cam sensor. Reset cam sensor to factory setting and test again.

 

[timdesu2000]

I pulled the cam sensor cover off of the assembly and checked the wheel for loose play. All was good. Due to the weather I didn't drive it with the cam sensor unplugged. I will bring my scope home from work and try to look at the patterns this week.
Thanks for all the info.

 

[turbo nasty]

Like dave says ...start car and with engine idling unplug cam sensor. This puts engine in batch fire and if it clears up. Your cap is bad. Recently, I had a car that started and idle fine but would stumble n pop around 2 k rpm and the cam sensor cap was the issue.