1994 k1500 wild misfire

[Murderedgtp]

Hey so I have a 94 k1500 with the 5.7 and I’ve replaced the rotor the cap and rebuilt the tbi unit. I had it running somewhat fine with one side oem plugs and one side hot plugs, but when I switched it to all oem it ran worse. Someone plz help

 

[thinger2]

Hey so I have a 94 k1500 with the 5.7 and I’ve replaced the rotor the cap and rebuilt the tbi unit. I had it running somewhat fine with one side oem plugs and one side hot plugs, but when I switched it to all oem it ran worse. Someone plz help

Damnit ill bite.
Why did you run it with different plugs on each side.

 

[Schurkey]

As always:

Verify fuel pressure, and assure the fuel filter is OK.

Make sure all the "tune-up" parts/procedures are OK. Cap, rotor, plug wires, spark plugs, PCV, EGR, EVAP, heated air intake systems all working properly. Initial spark timing OK, electronic spark advance working properly.

Assure the plug wires are routed as GM intends--including all the plug wire looms.

Replace the O2 sensor if it's got more than ~50K miles on it.

Look at the spray pattern of the fuel injectors. Should be a nice, even cone of fuel spray from each injector. At low speed, the injectors fire sequentially, but at higher speed this is so hard to see that they look like they're both firing all the time.

Connect a scan tool, verify EVERY sensor and computer output. Look at fuel trims. Assure it's got an RPM signal that varies with engine rpm, and never "drops out".

 

[name]

Assure the plug wires are routed as GM intends--including all the plug wire looms.

I am having the same issue with a random misfire as the OP after installing all new tune-up parts from Autozone ( Duralast Gold wires, cap, rotor and AC CR43TS plugs ) and came upon this thread looking for a solution. I did put a wire loom on the coil wire witch was resting on the #1 plug wire and it did help it out, but did not compleatly get rid of the miss. so I am thinking this recommendation by Schurkey is legit and would like to pursue it further .

The problem is, after searching for how to run the plug wires for a SBC I get diagrams that show a variety of ways, and none that show the wire looms. Like the OP, I also have a 94' K1500 5.7 ( Mine is a GMC suburban ) but need to know where I can get the right spark plug wiring diagram for the wires and looms ?

 

[Road Trip]

...so I am thinking this recommendation by Schurkey is legit and would like to pursue it further .

The problem is, after searching for how to run the plug wires for a SBC I get diagrams that show a variety of ways, and none that show the wire looms. Like the OP, I also have a 94' K1500 5.7 ( Mine is a GMC suburban ) but need to know where I can get the right spark plug wiring diagram for the wires and looms ?

Hello name,

There actually is 1 best way, and many many suboptimal ways to route the spark plug
wires on a SBC. Especially the ones in the GMT400 family, for the way these engines are
tasked vs the emissions calibration the secondary side of the ignition system is run right
up against the limits of the spark plug wire harness's ability to reliably contain/route the high
voltage pulses to the intended destination.

And if you want to see a visual version of the old 'Telephone Game' (children's game demonstrating cumulative error)
just wander around at the next local Show & Shine and look at how many different
ways the spark plug wires can be hung off of a 1st-gen SBC. Lot's of creativity,
artistic vision, or evidence of making it up as you go along, but at the same time a lot of reliability
vs routing rules are ignored/broken.

****

So in order to get the best guidance on this subject, let's go to the source and see how the General's
engineers recommended routing these wires in order to minimize cross-firing, shortened lifespan cats,
higher emissions, etc. Since you are working on a '94, I opened that year's FSM and did a global Find (Ctrl F)
on 'spark plug wires.'

Here's a detail on the passenger side from the FSM:

You must be registered for see images attach

And here's a detail illustration of the driver's side spark plug wiring:

You must be registered for see images attach

Note: Take a careful look at the effort to keep the wires from both firing order &
physical neighbors #5 & #7 as far apart as possible in the factory loom. There's an
important message in this illustration, direct from the people paid to worry about
this stuff for a living. (!)


Note: In the 1st attachment I took a big picture screen snap of what it's like to
search the '94 FSM for every instance of 'spark plug wires'. As you can see in the
upper right hand corner there were 20 instances of this phrase in the book, and
4/20 gave me what I was looking for. If you haven't given yourself the gift of
using the Factory Service Manual in order to keep your GMT400 on the road, then
run, don't walk over here to the forum's FSM cache and download a free copy for
yourself. (88+ GMT400 FSM cache)

****

But wait, there's more. I saved the best for last. There is a gentleman on this forum
who combines top-notch workmanship with way better than original levels of power
production. His work is his signature, and my great Uncle Hank would approve.

Follow this link to this reply, and study carefully how he routed his wires.
Hint: It's among the closest in the real world that I've seen to the guidance
out of the General's books. :0) (L31MaxExpress photos of his spark plug wire installation.)
NOTE: This guy routinely monitors his live data, including the misfires, so
his implementation details are based on hard data instead of wishful thinking.


****

Hope all this proves helpful in your efforts to eliminate those random misfires.

Best of luck --

 

[name]

Many Thanks for the quick and detailed reply, I will get out to the garage later today and compare what I got, with what the experts do.

 

[Road Trip]

Many Thanks for the quick and detailed reply, I will get out to the garage later today and compare what I got, with what the experts do.

Sounds good! By the way, bonus points if you find something amiss you then take clear photos and
share them here so that others can learn from it. Sometimes showing how it's not done is even more
informative than showing how it's supposed to be done. The whole compare & contrast teaching scenario.

Best of luck finding the root cause of your intermittent misfires...

 

[name]

Well, I made it out to the garage before I read Road Trips post, so I did not take any " before pictures " But this is what I found.

1) Half of the OEM wire clips that are shown in the above pictures are missing on my unit. There are some metal tabs ( #8 support in the photos ) where I believe the plastic wire clips go ( #9 Retainer in the photos) but the plastic parts are missing. The only OEM wire clips that I have left on my unit are the ones closest to the plugs themself.

2) I did have wire #5 and #7 running together , witch is a big NO NO

3) In the above pictures, It talks about "spark plug wire shield " coming off the 2,4,6,8 side plug wires, but my search for these " wire shields " only produced the Metal ones for the newer Corvettes and the cloth ones for running headers. So seeing how I had some success in wrapping the coil wire in a plastic loom, I figured that was what they were talking about and ran all the plug wires coming from the cap in 1/4" wire loom until the first Aftermarket wire divider that came with the wire set. Because I did not have all the OEM retainer clips I simply did my best to separate the wires with the plastic loom .

Here are the pictures of my current set up. Witch runs good when cold but the miss still comes back when it comes up to running temp.

 

[name]

1,3,5,7, side

 

[name]

New Dizzy and ICM, New Cap, New Rotor, New Wires, New plugs, New EGR valve, New IAC valve, it is not throwing any codes.

The only thing I have not replaced is the Coil but It did check out OK with an volt meter test. Are these coils noted for creating a miss when they warm up ?