99 Jimmy Misfires

[wigglewerks]

Misfires on cylinder 6 all the time. I checked the wire and plug and they look good. Is this a problem that appears when the fuel distribution unit goes out? I don't know what else i can check without replacing the $350 unit.

[MT-2500]

Welcome to AF.
We need more info.
What engine?
How many miles on tune up?
What kind of plugs?

Replace plugs and wires or switch them from another cylinder.
Check for good compression and spark to that cylinder.
Any vacuum leaks?

Is the plug wet or dry on the end?
How is the dist cap and rotor?
Check fuel pressure and camshaft retard setting.

Check for good injector pulse to that cylinder.
And make sure the injector is pluged in good and making cnnection.

If the injector is bad you do not replace the unit on that year they can replaced seperate.
Let us know what you find.

[wigglewerks]

Sorry about that but thanks for the greeting
It's a 4.3l vin W, I tried switching plugs and did not follow but could not switch wires cause it's a straight boot and all the others are 90 degree boots. But I put a plug in it and grounded it to see good spark. After running for a few minutes found the plug was slightly wet. Compression is good at 180. How do i check the injector pulse? I though the injectors were under buried under the upper intake. No vacuum lecks that i can find. If it was avacuum leak wouldn't it be a random misfire instead of always on #6?

[MT-2500]

How many miles on plugs and wire?
Good Ac delco plugs?
If the plug is wet is INDUICATION OF WEAK SPARK OR OR BAD PLUG.
Is it gas or coolant or oil on plug end?
Check plug wires and cap and rotor.

You can check for injector pulse at the 2 wires for no 6 going into top of intake

[wigglewerks]

I was able to sway wires from a friends car, the misfire is still on #6, Unknown miles on plugs and wires. THe plugs are acdelco but are good spark. I looked under the cap and the cap and rotor dosen't look to bad.
Checked the injector pulse and it is pulseing good. Ohmed them out and they are all 11.5ohms. Thanks for helping me. Hope i am giving you good info.

[MT-2500]

Can you feel the miss or does it just show on the scanner?

Is the fuel pressure up to par?

[wigglewerks]

Both Feel and scanner. I don't have a tool for fuel pressure testing

[MT-2500]

Originally Posted by wigglewerks

Both Feel and scanner. I don't have a tool for fuel pressure testing

Borrow/rent/buy one.
Some parts places loan tools.

If plug is wet with gas on end that cylinder is not firing good.
Recheck plug cap and rotor and wires and compression and for vacuum leaks.

With A good scanner and a fuel pressure gauge you can run a injector test.
And also check the camshaft retard setting with the scanner.
Good Luck

[wigglewerks]

Checked fuel pressure and found within specs that a friend at GM told me. installed new spark plugs, wires, cap and rotor. Also bought the mfi conversion, and installed that. Misfire was present with the tune-up, and corrected the misfire with the new crab unit. thanks for the help

[knottybuoyz]

Originally Posted by wigglewerks

corrected the misfire with the new crab unit.

I've got the same problem with a '99 Jimmy. Engine was rebuilt a yr ago and the symptoms started then. They seem to appear when it's cold and damp and go away once warm and dry. Mechanic who rebuilt and serviced this truck since new is stumped.

What's a crab unit?

[wigglewerks]

The crab unit is the same as the sypder unit. Its the fuel injection unit in the intake manifold. The fuel comes from the tank and is distributed in this unit. I think the correct term is the "fuel meter body"