Misfire, runs like poop

[mockspeed88]

So I had the truck running pretty good. A slight hesitation off idle. Then it developed a constant misfire. I checked the plugs (fine), wires are new Napa premium. Distributor is a new duralast gold (second one) but I put in a gm genuine icm.

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[78Monte]

I put in a duralast gold last year and The ICM was bad out of the box, I swapped out the ICM for another one I had on hand and the trucks has been running great since.

How old is your genuine GM ICM?

 

[mockspeed88]

Just bought it this morning. Truck ran perfect for 5 minutes, warmed up and have a misfire throughout the Rev range. I believe my next goal is to goto the junk yard, the junk yard by me has a bunch of tbi 350s in it including a text school training truck with 295 miles on it. So I am going to pull a distributor and ignition coil

 

[78Monte]

How old is the distributor? you mentioned this is the second one?

 

[mockspeed88]

A month. First one I bought in October, and within 4 months the points on the cap were already green and corroded. So I pulled it and returned it. The icm lasted a day, I replaced that with a fancy car quest premium one, the when it developed the misfire I bought the gm genuine parts one.

 

[Schurkey]

Make sure you keep replacing distributors and modules, and maybe a coil--without doing any diagnosis.

Absolutely do not perform a cylinder-balance test by sequentially shorting-out the spark to each cylinder in turn, and watch a vacuum gauge to see how much the intake vacuum drops with each cylinder. Any cylinder that gets shorted but doesn't drop vacuum is dead; a cylinder that's shorted and doesn't drop vacuum as much as the others is weak.

Do not connect a scan tool and view the data stream. Don't verify every sensor, and don't assure that the computer outputs seem reasonable.

Do not verify fuel pressure.

Do not check for vacuum leaks at the accessory hoses like power brake hose, or PCV hose; or inspect for failed intake manifold gasket(s) or throttle body base gasket.

It's completely possible that you've had multiple distributor/module failures, and replacing the coil and the module together could fix it. And if not, maybe you got more defective parts. Try again. And again.

 

[mockspeed88]

Well where do I find this scan tool for a reasonable cost? It's obd1 which aren't in abundance anymore. I replaced every vacuum hose. Fuel pressure was checked its 12psi. Throttle body was rebuilt with a full kit, brand new gasket on the base. I replaced the ecm with another one out of the junk yard. I have tools, but not the budget to buy multiple vaccum gauges, $1300 dollar gm tech 2 scan tools, and like I'd be able to accurately decifer what the scan tool is displaying. I'm not a master mechanic with a huge knowledge base of working for 30 years at a gm factory or dealership. But that's why I post on here, to tap into others knowledge and experience and to see if others had simular issues and what they accomplished to fix these issues.

 

[df2x4]

Well where do I find this scan tool for a reasonable cost?

Chinese clones of the Tech 2 can be found with a little searching for $350 or so. There's also adapters and software like VXDIAG/Tech2Win which will emulate a Tech 2 on a computer for about half that price. I know @Schurkey has recommendations for used Snap-On tools that will do OBD1 as well.

 

[Supercharged111]

Well where do I find this scan tool for a reasonable cost? It's obd1 which aren't in abundance anymore. I replaced every vacuum hose. Fuel pressure was checked its 12psi. Throttle body was rebuilt with a full kit, brand new gasket on the base. I replaced the ecm with another one out of the junk yard. I have tools, but not the budget to buy multiple vaccum gauges, $1300 dollar gm tech 2 scan tools, and like I'd be able to accurately decifer what the scan tool is displaying. I'm not a master mechanic with a huge knowledge base of working for 30 years at a gm factory or dealership. But that's why I post on here, to tap into others knowledge and experience and to see if others had simular issues and what they accomplished to fix these issues.

You can look into ancient WinALDL stuff too.

 

[PlayingWithTBI]

Or a laptop, an ALDL/USB cable, and TunerPro RT - total investment $60, less the laptop. Then, some research on how to configure and use it.

OBD Diagnostics

aldlcable.com

TunerPro and TunerPro RT - Professional Automobile Tuning Software

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Tutorials, Write Ups, Tips and Questions!

www.gearhead-efi.com