About a year ago I posted about my 91 Firebird 5.0L having an idle "miss" that could not be solved. With your help and after replacing everything under my hood that could possibly contribute to a bad idle the problem persisted. In fact almost all 5.0L TBI's have this idle "miss". I recently took a diagnostic class by Snap-On that featured an instructor that does diagnostic trouble shooting for GM, Ford, and Chrysler on new vechicles at the factory. The instructor also has his own shop on the side. Anyway! I asked him about the 5.0L miss and another class mate had an 88 5.0L Camaro to test with the same problem as my bird. After using the scope and speaking with the instructor I have discovered that the injector drivers in the ECM on 5.0L F-bodies and 5.7L trucks have transistors that start to short out. A new ECM does not always fix this due to remanufacturers not checking injector drivers. Although a 73 cent capacitor in parallel with each injector will suppress the problem and keep the injectors from bouncing off of their seat at idle and that's not all we found! The distributor shaft on GM TBI's gets magnatized and supresses the trigger pulse signal! The fix? Get a new shaft from GM and walla the trigger voltage goes from 6 crappy volts to about 30 where it should be! This did fix the idle problem and the Camaro drove like new after these changes. If you would like the capacitor number I can get it to you, just ask. I just thought you might find this interesting.

------------------
84 Camaro ZZ4 with HOT cam. Ported Heads, Installed Larger Race-Flo Valves, RPM Air Gap Intake, and 1 3/4" SLP Headers (Best 60',Quarter Mile, MPH) (1.88, 12.91, 106.77)
Other Mods: You name it and I have probably changed it.

2001 Dodge Ram Quad Cab 5.9L 4*2

The Bowtie
ASE Certified Auto Tech
LIVE AND DIE BY THE ALMIGHTY BOWTIE!

 

I knew about the injector drivers, didn't know about the capacitor. Thats interesting. Unfortunatly, if I were to come accross another w/ that, I wouldn't be able to install the capacitor, because its not "GM Approved", so another ECM it is.

I havn't seen the reluctor wheels loose magnatism, usually just crack. But I guess being cracked disrupts the magnetic field anyway, but yes, a new distributer would fix it. You say you got just a shaft? I never saw just the shaft for sale. Usually you get teh whole distributer.

Thanks for posting your findings, its always interesting to see what is fixing what.

------------------
FREE CARFAX Record Check

If you live in Southeastern US, check us out!
South East Thirdgen

GM Master Tech
ASE Master Tech + L1
Savannah, GA

'87 Trans Am
S/D TPI retrofit including functional PassKey,
22# injectors,
Whatever chip I feel like burning,
JET AFPR, Ported Plenum,
TB Coolant Bypass, Custom Cold Air,
SSM SFC, KYB Shocks, Boxed LCAs, Wonder Bar,
8mm Accel wires,
Flowmaster Exhaust,
16" GTA rims,
Corvette Servo,
3.73 Posi
4wheel Disc Brakes
Summit 1-5/8" headers, 2.5" Dynomax catback.

Best 1/8: 9.519@72.74

'97 Bonneville SSE

 

Curious, any effect on a TPI car?

------------------
Mike

'90 IROC-Z , 5-speed, ZZ4, G1 Trick Flows
Moderator SEThirdgen