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Testing Park Ave 3.8L coil packs

In the never ending effort to fix the "Herky-Jerky" problems with the '95 Park Ave the dealer reported the coil resistances "out of spec." "Will that fix the problem I ask?" He says "Not sure, but until we replace those bad coils we won't be able to further diagnose the problem." So, I told them to do it and save the coils for me. Since I am writing this note you probably can guess that it didn't fix the problem.

I looked up the specs on AllData and did my own measurements. I get around 0.4 Ohms on the primaries and around 5600 Ohms on the secondary. AllData says it should be 0.5-0.8 on the primaries and 5000-8000 on the secondary.

While the primaries are out of spec I'm wondering if replacement really was indicated. For one thing, it's tough to accurately measure resistance in the range of the primary. I have two digital multimeters and one measures 0 ohms as 0.3 and the other as

0.6. Naturally, I subtract the 0 value from my measurements, but would not bet on the result being accurate to anything better than +/-0.2 Ohms. I also doubt that the tech had anything better to measure with. I would imagine one would need a decade box and a Wheatstone bridge to get a reliable measurement in this range. And, all 3 packs are very close to the same value. My guess is I'd get the same measurement on the new ones. I'm a little reluctant to test them since they have to removed for the primary measurement, and the dealer might tell me that would void the warranty on their work.

So, should I go back and argue with them? Should they put my old coils back on and resume the diagnosis I paid them $88 for, in addition to the $108 labor they charged to replace the coils?

For newcomers wanting full background look for prior "herky-Jerky" post. Basically, it's an intermittent miss in the engine or something that seems to get amplified by driving the torque converter clutch control nuts.

Ed

Reply to
Ed
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Reply to
Shep

Testing DC resistance _often_ will not tell you if the coil is bad or not. It just tells you the DC resistance. Insulation sometimes breaks down when the coil is hot or under stress running a 30 kv ring voltage through it. HOWEVER, since there was no change in the "herky-Jerky", your old coils were probably good. I would ask them to put them back on and get some sort of refund.

Reply to
« Paul »

It's a '95. No Check Engine Light. Scanner (just got yesterday) reports no problems.

replaced plugs, wires, fuel pressur regulator, MAF sensor, coolant temp sensor, and coils. I checked the EGR voltages. They looked OK to me, following the AllData guidelines. Have not figured out how to do the full EGR test shown in AllData... Don't think my Actron scanner will let me do all that is called for there.

Thanks. Wife is pressing me to hand the problem to the Toyota dealer and drive home in an Avalon. Looks tempting. This has been going on for months.

Ed

Reply to
Ed

I've read your old post about this problem. First off go out and buy a bottel of this

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your TCC is the problem this should take care of it for a temp fix. Ifit does fix it you know your transmission will need to come out andrebuilt. Other wise I would be looking into the EGR vavle. It might justbe dirty and sticking. A shop should be able to tell you that info withouttaking much apart. Also have you ever changed your fuel filter? That wouldbe another idea it might be plugged up. If it is be ready to stick a fuelpump in after replacing the filter.

Reply to
scrapir

Ed,

Just becaus the wires and plugs were changed doesn't necessarily mean that they are good. I had the same problem on my '94 Silhouette. I had a slight jerk/miss when under load (slight incline around 50 MPH). I had just changed the plugs and wires. Since I had to have the transmission rebuilt during this time, I thought they put in a bad tranny, or the TCC clutch was sticking. The trans shop looked at it 2 or 3 times, and nothing was wrong with the tranny. I sprayed some water mist over the plugs in the dark, and notices a very pretty arcing show, again!.

Pulled the plugs again, and notice one plug was misfiring (there was a carbon trail along the insulation from the tip to the ground). Replaced all AGAIN and the jerk/miss went away.

Good Luck, Bill

Reply to
wfyehl

Thanks for taking the trouble to dig out the old posts and make the thoughtful suggestions below.

I have read about related EGR valve issues. I did the voltage tests recommended in AllData, such as I could. The reference voltage is good... 5v. The test procedure also calls for using the Tech I tool (a special GM scanner I presume) to set the valve in various positions and take voltage readings, but I have not been able figure out how to do that with my newly acquired Actron CP9145 scanner. I almost won a new valve on eBay but someone else (perhaps with the same problem) beat me out. Dealer price is $200+. Maybe I'll ask the dealer to do the EGR tests to make up for his bad call on the coil packs.

Fuel filter and pressure regulator have been replaced. That was my call, having read here about that possible cause of the missing. Later I subscribed to AllData and learned that the rail pressure should have been measured with engine off, whereas I had done it at idle. So the regulator was probably OK in the firsts place. The tech said the filter looked clean, and since rail pressure was in spec he had no basis for recommending pump replacement. As you know, this is expensive since the tank has to be removed.

I am still interested in the problem, but I have now decided to get a new car. The PA has

105K on it and from all that I have read here there are potentially other problems lurking, e.g., the intake manifold gasket thing, the prospect of that supercharger drive coupling getting noisy again, and the tranny needing an overhaul. I hate to say it, but the new one will not be a GM product.

Thanks for your help. I appreciate it.

Ed

Reply to
Ed

Just to wind up on this...

I measured the primary winding resistance of the old coil packs and the new using a more accurate technique called the Kelvin method. With this method a

2 Watt 100 Ohm resistor is put in serise with the coil primary. The 100 Ohm resistor basically sets the current, and then the voltage drop across the coil primary allow accurate calculation of the coil primary resistance to 3 digits. The upshot is the new and old coils are very, very close. 0.368 Ohms vs. 0.347 Ohms. Both are outside the so called spec range of 0.5- 0.8 Ohms given in AllData. My guess is the spec is based on the coil at operating temps, whereas my readings are at room temperature.

Anyway, I'll be going back to the Buick dealer with some arguments for an adjustment. I don't think the new coils were warranted based on careful measuremenst, and the problem is still there.

Ed

Reply to
Ed

Ed, you've got my sympathies. You've been chasing this for too long now. I've been contributing to and/or watching this thread since you started posting about the herky-jerky. About now I think I'd suggest you check the air pressure in the rear passenger seat, or maybe put a lower wattage in the rear license plate light. Anyway... I certainly would go back to the dealer and approach them about a credit. I'd like to believe they'd work with you.

Reply to
Mike Marlow

If you feel up to it take the EGR vavle off and look for a carbon build up. In the center of it there will be a vavle you can push down with a pen. Move it down a few times it should move easy and it shouldn't get stuck anywhere. If it does it's probably bad.

Reply to
scrapir

Mike,

OK, dealer's got the back seat out, but the tech can't find the air-fill stem. Pls advise...

I'm pretty sure they will do something. This is the dealer that replaced the AC compressor a year after the warranty had run out because the one they replaced while under warranty lasted only about a year and a half. So they're good people. However, this problem is a deep one. I think a lot about it and concluded it is a fundamental design flaw in the engine ignition or EFI, combined with a poor implementation of OBD - II that fails to bring up an error code. I now have a scanner now (soon to go back on eBay, BTW) and when I drive around with it hooked up I see "no codes present" immediately after it stumbled.

Thanks for your support.

Ed

Reply to
Ed

I'll do that. I've been tempted anyway because I've picked up vibs from several sources, including this NG, suggesting an EGR problem Also, AllData shows a bulletin where the EGR valve diagnosis chart was modified to help track down an internal fault. GM wouldn't have done that if they hadn't experienced a lot of problems with it.

I will also pull the plugs out and replace them again, thinking they may have fouled due to some other problem that got fixed along the way. Also, most dramatic effects on drivability have been seen after replacing the plugs and wires the first time, and after later replacing one of those plugs that had mysteriously stopped firing.

Thanks for your support. Ed

Reply to
Ed

It's location is detailed in the Super Secret TSB. Can't publish the TSB number or it wouldn't be Super Secret anymore. Tech must not have gone to the Super Secret training on that day.

That's good Ed. My local Chevy dealer is the same way. You read so much about folks complaining about dealerships because they didn't get something they thought they should get, or because they want something for nothing and I find myself defending dealers more than I wish was necessary. By and large, my experiences with dealers has been just fine. Glad yours is going the extra mile for you. Relationships like that pay off in the end.

Reply to
Mike Marlow

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