Slight miss 1500-2000 RPM **FIXED** - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-24-2005, 09:21 AM   #1
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Default Slight miss 1500-2000 RPM **FIXED**

I drove up to Michigan yesterday to get a hitch from a fellow member (vital 49 is a great person to work with) and I noticed a miss in the engine at anything less than 70 mph. It does not backfire or anything, just not running smooth. Then around 2700-3000 RPM it has a noise I can only describe as static from the engine compartment. Maybe ignition pinging? I checked the plugs, and they are all good, the tips are white (running hot? I forget what that means). I also replaced the O2 sensor since all of this is accompanied by really poor MPG (20 on the highway, 16 in town ) but that didn't fix anything.

The car is a 1990 LE, only 75,000 miles. It also has a recent catalytic converter and fuel filter (within 10,000 miles). I am thinking it either has to do with the system that controls the spark or injectors. Everything mechanical is in good shape from what I can tell.

If you have any ideas let me know. Thanks
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Old 03-24-2005, 10:29 AM   #2
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Not really sure... That does sound like a spark related issue... Almost like you have a intermintent dead cylinder... could range from the coil pack to the plugs and wires... I have seen these coils go bad many times.... You wouldn't by chance have another Magnavog ignition or a type 2 ignition to swap on there to help you troubleshoot would you?

If you had a missfire to begin with, then the O2 would do nothing for you... When you have a dead or weak cylinder the ECM see the low oxygen content and throws more fuel into the mix... We need to find where the real problem is... Most of these bonnies will do 28-31 or so on the road... I have done as good as 31 with the AC kicking and me driving a little fast...

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Old 03-24-2005, 11:53 AM   #3
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Is it only at higher RPM? Sounds maybe like the coil pack is loose and that causes that weird feeling. There are three bolts under the bracket and just check 'em to make sure they are all there and tight [I think they are 10mm, but don't quote me on that]. But yeah, you need a spare ICM + coils to test this. If you don't mind taking a little trip, I have one here [I live about 45min from valpo] you can test with [works fine, but that'* about it].


-justin
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Old 03-24-2005, 01:15 PM   #4
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I wouldn't mind doing a type 2 upgrade. Cold starts are not the best lately either, usually about a 5-10 second crank time. Plug wires were new a year ago, so maybe it is a coil. Still no check engine light, but the fact that a problem would throw more fuel into a weak cylinder sounds like the kind of symptoms I am having. I still have a hole in my radiator so I think I'll pass on driving up to MI again this week, thanks for the offer. (MPG is bad with fuel and antifreeze now ) No worries, I got one off of ebay for $56!

Could it be that the ecm is not changing my timing as needed? (I think I remember reading something about that in an old post, I may be completely wrong ) That would account for the strange noise around 3000 RPM too then. Like I said before, if enough signals point towards the coil pack, I'll do an upgrade since I have been wanting to anyways and see if that can take care of a few things at once.

Thanks for the input!
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Old 03-24-2005, 01:45 PM   #5
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That'* your coil or ICM dude. 5-10 sec crank time? Holy **** dude, I have never had a crank time above .5 sec. Turned over twice and fired. $56 for the Magnavox ignition? Dude, no offense, but you got RIPPED. Unless you got it new or something. I can get those $5 a pop, and fill a trunk up with 'em. That'* how abundant they are in this town.


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Old 03-24-2005, 08:08 PM   #6
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No way would I pay $56 for a magnavox ignition, I paid that for a new radiator . I don't even plan on buying another magnavox at all, I am going to look around the old posts and get the upgrade ready to go. I really wanted to do that anyways, now I have a good excuse!

If I buy new coils, which brand should I get? Anyone have much experience with aftermarket coils? I saw Accel on the Autozone website, Wells are about half the price...

Thanks for the input.
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Old 03-24-2005, 09:11 PM   #7
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I have Accel coils, I have heard reports of them prematurely failing, but I bought mine used, and they are great. No problems after 300-some miles. Didn't drive the car much in Fall.. me being 14 and all.


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Old 03-25-2005, 02:40 AM   #8
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The 5-10 second crank time was all to familiar to me. Upgraded to the Delco unit, and got new wires and plugs. Fixed it right up.
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Old 04-01-2005, 07:28 PM   #9
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I got a set of coils and a module off of a 1997 Buick. I got it mounted up fine, car started
fine, but the miss is still there and getting worse. The plugs look good, kind of white
looking, does that mean anything? The wires pass the visual test (they don't look very
old) but they have been on there for the 25,000 miles I have owned the car.

Should I go ahead and try new plugs and wires? I really don't want to keep throwing
money at the car, but I need to get rid of the miss.

Thanks!
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Old 04-01-2005, 08:37 PM   #10
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White plugs usually indicate they are running too hot. Check the gaps on them to see if they are right. If you don't know when they were last replaced, just do it. It is inexpensive and easy. If the the car is stock, just get regular AC-Delco plugs (forget part #). Make sure they are gapped at .060".
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