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ase_master327, Shop Owner
Category: Chevy
Satisfied Customers: 5288
Experience:  +15 years experience with Chevrolet. Bumper to bumper diagnosis & repair.
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94 chevy 1500 replaced plugs wires distributor cap, iac valve,

Resolved Question:

94 chevy 1500 replaced plugs wires distributor cap, iac valve, and still misses when running. what else could it be?
Submitted: 7 years ago.
Category: Chevy
Expert:  ase_master327 replied 7 years ago.
Well.. you can have vacuum leaks, or low compression in 1 or more cylinders, or even still a messing up sensor if you did those repairs right. You could still have other problems.. I am getting at, if the engine light is on, it will help point us in the right direction.. So is it?
Customer: replied 7 years ago.


Expert:  ase_master327 replied 7 years ago.
OK.. how do you know it is misfiring?.. I mean.. what is it doing?
Customer: replied 7 years ago.

When idling, it runs fine with no cutting out. When you start pulling out it starts cutting in and out, like a timing issue. Checked timing, it's fine. Cylinder compression test between 135 and 140. Checked codes, said the IAC was bad, changed that. Plugs and wires were old, that's why I changed them. The only thing I didn't change was the electronic ignition in the distriubutor. It's not backfiring through the carburetor.

Expert:  ase_master327 replied 7 years ago.
OK.. I thought I had a good idea of what was happening until you said.....Carburetor?
.. or did you mean TBI?
Customer: replied 7 years ago.
Sorry yes TBI
Expert:  ase_master327 replied 7 years ago.
OK.. There re some likely things that can heppen to this 'unit' for 1, I have had to replace MANY sets of injectors in these for similar problems. Also, I do not see where you changed the fuel filter.. if it is clogged, this will happen also.
Another thing is that the TPS might not be putting out a 'steady' signal.. it could have a 'drop' in voltage from just being worn out on the inside.
Still another thing is that the EGR valve is not opening, or the ports are clogged.
Here is a picture of the diagnostic steps for when an engine stumbles on acceleration, because I know there are some things I forgot to mention:

So. what I would do to start.. is run the engine and pull each plug wire off (one at a time) while the engine is idling, and see if ALL cylinders change the way the engine idles when you pull the wire loose from the distributor cap. If they do, then all cylinders are working. If you remove one and the idle of the engine does not change.. then we will look into that cylinder a little closer.

If I have been helpful (so far) be sure to click Accept, so I can get credit for helping you.. and THEN, if you need more help with these test procedures or anything else, just let me know.. Fair? Cool
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