[SOLVED] 1995 k2500 7.4 TBI running HORRIBLY

[Cuckfield]

You need a DC voltmeter--which will probably be part of a multimeter including AC and DC volts, Amperes to about 10 amps, several Ohms ranges, perhaps capacitance, perhaps a "battery testing" (AAA, AA, C, D, 9-volt) set of ranges which puts a small load on the battery when testing it's voltage, that sort of thing. Features vary with the meter selected. There's a million choices, and almost all of them are going to be cheap Chinese even if they're not inexpensive.

You will need either fine-wire "back probes", or a "test harness" that you can pierce the insulation and not damage the actual vehicle harness. The "back probes" may or may not be included with the meter you buy.

You'll turn the meter on, and select a DC voltage range that's as low as it goes and still accommodates 15 volts. On MY meter, that's the 40-volt scale, but other meters might have a lower voltage range--20 or 24, perhaps. A 6-volt scale won't accommodate 15 volts, so that's too low.

Testing the power supply TO the pump will require grounding the black meter probe, (preferably at the negative battery terminal, using a length of ordinary primary wire as needed) while sliding the red back-probe pin into the connector, past the silicone-rubber seal, so that the back-probe contacts the metal pins of the connector, and the meter is connected to the back-probe pin(s). You'd probably run the engine at this point, so that the pump is running, and you'd read the voltage on the meter. The alternator is likely charging at 14+ volts, so you'd better have 12.0 volts or more, showing on the meter. Remember, you're not testing the harness between your test point and the actual pump--the harness going up and over the tank, and the in-tank harness. A problem there is "invisible". But this is the best you can do without damaging the vehicle harness or dropping the tank/lifting the bed.

When testing the ground side, you'd do essentially the same thing. Ground the negative lead. Touch the red probe to the ground wire conductor as close to the pump as you can reach. This will require piercing the insulation of that wire, and you'll have to "patch" the insulation with something--"liquid electrical tape", real electrical tape, a dot of RTV silicone, etc. You're looking for the lowest value--under one volt, less is better.

Fantastic write up. Didn't know using one was so easy! Gonna go out and buy a multimeter with back probes tomorrow.

 

[Schurkey]

Trying to visualize this...
got a pic?

No. But in this case, it's three, one-foot long 16-gauge wires with "male" and "female" Weatherpack connectors on each end to fit into the existing harness connector. Then you can pierce, strip, mutilate the extension harness leaving the vehicle harness un-molested.

If I can find my extension harness, I'll pop a photo. No promises.

 

[scott2093]

No. But in this case, it's three, one-foot long 16-gauge wires with "male" and "female" Weatherpack connectors on each end to fit into the existing harness connector

If I can find my extension harness, I'll pop a photo. No promises.

I see...so like a jumper in between that you can stab/probe?

 

[Schurkey]

Exactly.

 

[Cuckfield]

Tested fuel pressure with brand new gauge. Reads at a solid 30 psi, steady.
Gonna replace the ICM and see if that works.

 

[Cuckfield]

Consider replacing the ICM(ignition control module),you'll find it in the distributor.I've had similar problems with my '95 Burb and replacing the ICM would solve them.If you do replace it be sure to use an ACDelco part and nothing else.I recently had problems with wifey's '99 Burb and tried two Delphi ICMs and both were bad,put an ACDelco in it and it fired right up.

I replaced the icm with a genuine acdelco, and I replaced the ignition coil. Still running poorly. Any other ideas?

 

[scott2093]

I replaced the icm with a genuine acdelco, and I replaced the ignition coil. Still running poorly. Any other ideas?

I'd try to find and borrow an obd1 scanner. May be something glaringly obvious it could show. Not a code reader although it probably couldn't hurt to check if there are any stored...
Can't recall but, have you tried pulling any codes by jumping the aldl connector? Does your truck allow that?

also, ICM is mounted on the outside distributor in my 93. The nasty little troublemaker pickup coil is inside the distributor in mine....

 

[Cuckfield]

I'd try to find and borrow an obd1 scanner. May be something glaringly obvious it could show. Not a code reader although it probably couldn't hurt to check if there are any stored...
Can't recall but, have you tried pulling any codes by jumping the aldl connector? Does your truck allow that?

also, ICM is mounted on the outside distributor in my 93. The nasty little troublemaker pickup coil is inside the distributor in mine....

You can jump them. My service engine light IS on, upon inspection. Is there a list of codes to read?

 

[Cuckfield]

I'd try to find and borrow an obd1 scanner. May be something glaringly obvious it could show. Not a code reader although it probably couldn't hurt to check if there are any stored...
Can't recall but, have you tried pulling any codes by jumping the aldl connector? Does your truck allow that?

also, ICM is mounted on the outside distributor in my 93. The nasty little troublemaker pickup coil is inside the distributor in mine....

I have codes 32, 33, and 42.

 

[Carlaisle]

The parts you first replaced, do you still have them? If you put them back on and it runs differently you'll have learned something useful at no cost beyond your time. Swap out each individually so you can identify the specific failure point. You would not be the first person to receive new in box parts that are bad.

Did you reconnect the bypass?