97 K3500 7.4l spitting, sputtering, backfires, and stalls

[Agibson]

I didn't ohm it for ground. I didn't think 11.7v was bad for a 12v system.

Not sure what the knock count is I'll have to check it when I get off work.

But from power wire on the icm plug to ground on the battery was reading 11.7v with key on engine off

 

[Macs Garage]

Check your fuses? My truck was doing the same thing and the ecm 20a fuse blown.

 

[Agibson]

I've check the fuses multiple times. I was wondering if maybe the fusebox had corroded and not getting a good connection or if a relay is going bad.

 

[Schurkey]

11.7 is a volt down from a fully-charged battery at 12.6--12.7.

I could see a volt of voltage drop depending on where you connect the meter in the harness. I'm not saying that's good, I'm saying that's probably typical.

 

[94K3500PROJECT]

Make sure no damage/corrosion/burns to the ignition wire running to the starter solenoid.
Had similar issue in the past

 

[Agibson]

Ok I'll have to check that out. I was going to replace the battery wire to the starter anyway.

 

[Jeepwalker]

I didn't read through this whole thread ....but did anyone suggest water in the fuel? It can happen a number of ways and the results are what you've described. I've fueled up before and taken on a big 'slug' from the gas station. Same issue you described and I looked at EVERYTHING before looking into the fuel. It took a handful tanks of fuel and many bottles of gas-line antifreeze to work it out in my case.

Other items: Fuel delivery, Check cam timing (in case cam jumped a tooth), remove valve covers and inspect/measure rocker movement.

 

[Agibson]

Ok update checking the wires on the starter the small wire pulled out of connector real easily. Now question where does that wire run to?

 

[Schurkey]

Ok update checking the wires on the starter the small wire pulled out of connector real easily. Now question where does that wire run to?

Purple wire? (Sometimes fades to pinkish)

Depending on the vehicle, it either goes to the ignition switch via the neutral-safety switch or the clutch switch; or it goes to the starter relay in the "electrical center" near the left front fender.

I had a similar problem on my '97. The wire had been spliced before I bought the truck to repair corrosion, and it corroded again. Salt on the roads, and road splash are hard on the starter wiring. I cut the wire back as far as I could access it; and still had corroded copper. I had to splice about three feet of fresh wire from above the engine, and then drop the new wire down to the starter.

Wire from previous repair:

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Additional wire cut back as far as I could reach before the harness became inaccessible behind the engine. Even the "good" end is still too corroded:

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Broke the purple wire out of the harness above the engine, spliced-in a similar-gauge red wire (didn't have purple) and routed it down to the starter. Tucked and secured it to the original harness so it was protected from heat and chafing.

Crimped, soldered, shrink-wrapped.

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[GMTMark]

11.7 volts is too low imo. Start simple by checking the battery (should be 12.5 at least with engine not running). If the battery checks good then crank the engine and test again; you should be getting 13.5 to 14v. If not then you have either a bad alternator or bad positive wire from alternator to battery or bad ground. If all that is good then start testing the system from that point all the way through. I don't know of any reason why the voltage should drop most anywhere in the system. Test with engine running. Test voltage into the ecu, to the injection system, to the coil, to everything that makes it run. The fuel pump as well. I'm thinking somewhere there is corroded wiring or bad ground. if voltage drops anywhere along the system then there's your culprit. Always start simple and be careful not to burn yourself. Sometimes it's just tedious work and time consuming. Just my 2 cents.