95 pa jerking

[bejoly]

hi my 95 pa is and has been jerking. While cruising lightly on the gas and as i hit a slight incline in the road going about 45-50. i can step on the gas a little bit more and it will drop down a gear and be fine. my 92 pa did the same thing so i'm thinking it's just a characteristic of the cars but I do remember seeing a tech service bulletin on it. Any one have an idea. Thanx mark

[HotZ28]

Usually what you described is called "spark scatter", in mechanic slang.
By the way, “spark scatter” is caused by applying high voltage from the coils, to weak wires, or a high resistance in the plugs. Electrical current will travel the source of least resistance. In auto engines, that source is the nearest ground!

The problem is a common dilemma on these cars, due to the high final drive ratio and the lock up converter engaging at low RPM. Everything ignition and fuel related, has to be in top notch condition to overcome this problem. Even the slightest malfunction of any component will be noticeable while the engine is under load, and at low RPM.

I would start with the basics first, like plugs, wires, fuel filter and checking fuel pressure. That would be a good preventative maintenance function, if not recently done. You could also have a weak coil giving low voltage on one or two cylinders. Do the other items mentioned first and if that don’t solve the problem, try to isolate the problem to what cylinder is missing, and change the coil. Also, try some Lucus injector cleaner with your next three tanks of gas. (One tank, is usually not enough)

[jag_man653]

Originally Posted by bejoly

hi my 95 pa is and has been jerking. While cruising lightly on the gas and as i hit a slight incline in the road going about 45-50. i can step on the gas a little bit more and it will drop down a gear and be fine. my 92 pa did the same thing so i'm thinking it's just a characteristic of the cars but I do remember seeing a tech service bulletin on it. Any one have an idea. Thanx mark

I have the same problem in my '95 PA Ultra. Moreover, I have found many similar reports here and in other forums. I posted my story (still unfolding) at the alt.autos.gm Newsgroup, under the subject Herky Jerky. I have :

replaced the plugs and wires (yes, with good ones)
replace the fuel filter and pressure regulator
Replaced the throttle position sensor
Replaced the mass air flow sensor
Replaced the coolant temperature sensor
Replaced the coil packs

Some of this I did myself, but other things were done by a trusted independent and a GM dealer. The coil packs were replaced by the dealer due to supposedly being out of spec on resistance, but I then measured them myself using techniques far better than the dealer probably used and found them to be the same as the new ones to 3 decimal places. On these grounds and the fact that the problem remained, I asked them to put the old ones
back on and refund the charges, which they did.

None of this had any lasting effect on the problem. Throughout all of this there has been no Check engine light except once, and that was discovered to be due to the shop having put the wrong mass air flow sensor on the car.
The shops test drive the car with scanner attached and find no cods are being set. I bought a pretty good scanner and did it myself whth the same result.

Setting aside the engine miss theory, there being little else to pursue there, the car is now at the tranny shop. They assured me they would find the problem if there was one, but that was 2 days ago and still waiting to hear from them.

The only conclusion I can draw at this time is this is a serious and wide-spread problem with the Park Ave (and most likely with all the GM cars that use the same engine and/or tranny), but there has never been a technical service bulletin. Exacerbating the problem is the GM implementation of OBD II on the car is not good enough to even know anything's wrong.

I doggedly keep trying to fix it. My wife had a simpler solution, and we are moving forward with it: we will take delivery of a new Avalon next week.
Being a long time Buick family, going back to the '39 my father owned, we first looked at the Lucern. But, as nearly as I could see it has the same basic technology, if not the identical 3.8L engine and tranny, as in the 90s' Park Aves and La Sabers, delivering less power and having poorer gas mileage than the Toyota 3.5L DOHC variable valve timing and 5 speed tranny.

So, I sympathize with you and others with this problem. BTW, is you dual climate control system still working? There is a similar situation there.

Ed

[jag_man653]

Originally Posted by jag_man653

Setting aside the engine miss theory, there being little else to pursue there, the car is now at the tranny shop. They assured me they would find the problem if there was one, but that was 2 days ago and still waiting to hear from them.
Ed

Just got a call from the transmission shop. They drove the car for 2 days with whatever scanners or test equipment they use and found nothing wrong with the transmission. That was good news in the sense that I really was not looking forward to a $1200 rebuild job, but bad news because I still don't know what's causing the problem.

Forgot to mention before I also looked into the EGR valve, making voltage measurements per a tech bulletin found in AllData. It tested OK. And, I put a fuel pressure gauge on it and found pressure to be within specs. Some have said it could be the fuel pump nonetheless, since it's intermittant and it's nearly impossible to monitor fuel pressure while driving around. Injectors? Possibly, I suppose, but seems unlikely.

Ed

[HotZ28]

For those of you who have tried everything external, to overcome this problem, I would like to suggest that you check the timing set. If the timing chain is loose, or if the magnet is cracked, or partially missing, the injector timing will be out of kilter and therefore cause the same symptoms as you have described here. When I first bought my PA Ultra (used), it ran very smooth, until one night I decided to open it up on a 4-lane highway (no other cars on the road) reaching speeds in excess of 110 MPH +, then all of a sudden, the perfect running engine changed. I continued to drive it for several months without any codes, but it had an erratic exhaust note and surge or misfire under load. Finally, after several months, it spit out a code 41. Upon further investigation, we found the cam gear magnet was shattered and the timing chain was stretched, which would cause the timing to be retarded. We installed a new timing set, along with a cam sensor, and it has been running like a new one ever since. This was very hard to diagnose in the beginning, since all sensors and pressures were within specification. This is a common problem with the 3.8 in excess of 100+K. Just another thought and experience I wanted to share.

[jag_man653]

Originally Posted by HotZ28

We installed a new timing set, along with a cam sensor, and it has been running like a new one ever since. This was very hard to diagnose in the beginning, since all sensors and pressures were within specification. This is a common problem with the 3.8 in excess of 100+K. Just another thought and experience I wanted to share.

Thanks. Sounds like a big job. Since I have never pressed the car as you describe, would you think it likely in my case? We got the car with 20K miles
in '97, and the shudder appeared for the first time about 6 months ago.

Can I check the timing set myself? I have a timing light and an Actron
9145 scanner.

Ed