How can you tell if you have a miss?
Thread Starter
Member
Joined: Nov 1999
Posts: 100
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From: Burbank, IL, USA
How can you tell if you have a miss?
The RMP at idle is steady but the car shakes like mad? '89 L98, mods in sig.
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1989 Iroc-Z L98 Original engine-58K miles!!
SLP 1 3/4 SS headers, Hooker Areochamber catback, no cat, BBK AFPR, Hypertech 160* fan switch, ported and gasket matched plenum, TB coolant bypass, relocated MAT sensor, screenless MAF sensor, K&N filters, Accel cap and rotor, Taylor SpiroPro 8mm wires, Bosch Platinum plugs, Mobil 1 Synthetic 15W50 motor oil, and more to come...
Best ET- 14.24@96.76MPH / 2.17 60ft on street tires with the crappy B/W 2.77 gears.
Homepage currently under construction: http://www.iit.edu/~wicktho/len
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1989 Iroc-Z L98 Original engine-58K miles!!
SLP 1 3/4 SS headers, Hooker Areochamber catback, no cat, BBK AFPR, Hypertech 160* fan switch, ported and gasket matched plenum, TB coolant bypass, relocated MAT sensor, screenless MAF sensor, K&N filters, Accel cap and rotor, Taylor SpiroPro 8mm wires, Bosch Platinum plugs, Mobil 1 Synthetic 15W50 motor oil, and more to come...
Best ET- 14.24@96.76MPH / 2.17 60ft on street tires with the crappy B/W 2.77 gears.
Homepage currently under construction: http://www.iit.edu/~wicktho/len
TGO Supporter
Joined: Aug 1999
Posts: 14,811
Likes: 1
From: Jackson County
the ecm will correct for dead cylinders. i took a class on ecm controls and scanners when they first came out and the instructor unhooked 3 of 6 plug wires and the car still started and ran, and idled smooth and didn't shake. for your problem try pulling a plug wire and see if it changes anything. hopefully it will so you'd know that cylinder was working. if you get changes and then one doesn't there is your problem.
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-=ICON MOTORSPORTS=-
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-=ICON MOTORSPORTS=-
Moderator
Joined: Jan 2000
Posts: 19,651
Likes: 309
Slow,
By the description of your symptoms, it certainly sounds like you have a miss.
Do as Ed suggests. Remove a plug wire one at a time to determine if a cylinder is producing power or not. If you don't have insulated spark plug boot pliers, be very careful, since you'll likely become the path of least resistance to ground as soon as you remove a wire.
Another way to perform this "power balance" test on a TPI is to remove the electrical connector from a fuel injector instead of a plug wire. This is much safer for the mechanic and certainly less painful. It will not cause problems for the ECM.
As Ed advises, if you remove an injector connector and there is no change in idle speed or quality, that cylinder is not producing power. If the idle drops briefly when you remove a connector, reinstall it and move to the next one. One or more of the cylinders is probably going to be "dead".
Don't feel bad. My '86 TPI did the same thing with less than 20,000 miles on it, then again after 42,000 miles. Both times, I had plugged/restricted injectors. I think my problem is the fact that the car is stored so much, allowing fuel deposits to build on the injector tips. Judging by the accumulated mileage of your car, it probably gets its share of down time as well.
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Later,
Vader
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"Make Me Bad"
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By the description of your symptoms, it certainly sounds like you have a miss.
Do as Ed suggests. Remove a plug wire one at a time to determine if a cylinder is producing power or not. If you don't have insulated spark plug boot pliers, be very careful, since you'll likely become the path of least resistance to ground as soon as you remove a wire.
Another way to perform this "power balance" test on a TPI is to remove the electrical connector from a fuel injector instead of a plug wire. This is much safer for the mechanic and certainly less painful. It will not cause problems for the ECM.
As Ed advises, if you remove an injector connector and there is no change in idle speed or quality, that cylinder is not producing power. If the idle drops briefly when you remove a connector, reinstall it and move to the next one. One or more of the cylinders is probably going to be "dead".
Don't feel bad. My '86 TPI did the same thing with less than 20,000 miles on it, then again after 42,000 miles. Both times, I had plugged/restricted injectors. I think my problem is the fact that the car is stored so much, allowing fuel deposits to build on the injector tips. Judging by the accumulated mileage of your car, it probably gets its share of down time as well.
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Later,
Vader
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"Make Me Bad"
Adobe Acrobat Reader 4.0
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