Engine electrical issue

[68Chev]

89 Chevy K2500 4x4, 350 TBI, TH400 transmission. 250K miles

Have had progressive issue with motor stalling and dying. Started several yrs ago, intermittently (2 or 3 times yearly) would stall and die as I approached stop light and motor idled down. Would restart fine early on, then started having trouble starting after stalling at light, but would re-start after 1 or 2 attempts.

Issue progressed to misfiring, stalling and dying after warm up. Would also run same at cold start occasionally. Now stalls and dies after warmup, 5-10 minutes at idle.

Have r/r'd numerous parts and corrected several issues. Replaced following components: Distributor, ign coil, temp sensor, oil press sensor, oil pressure gauge sensor, MAP sensor(except MAP filter), TPS, IAC, knock sensor, O2 sensor, spark plugs/wires, EGR valve, PCV valve, fuel pump fuse at firewall. One fuel injector replaced, other tested and flow matched at shop. All vacuum lines checked. Checked fuses at fuse box.

Replaced fuel pump and filter. Had minor leak at fuel pump and ground wire was broken at connector at top of pump. Tested fuel pressure at TB after fuel pump r/r, checks at 12 psi.

Inspected battery, all motor grounds (cleaned and replaced several grounds but most looked healthy).

Rebuilt throttle body, replaced fuel metering valve, and had throttle shaft line-bored and re-bushed by shop. Throttle shaft had some play.

During t/shooting and parts r/r, issue has changed some. After stalling and dying, with key still on, pass side injector will begin to click intermittently. Swapped injectors from one side to other, both injectors now have same intermittent clicking, but left side injector occurs most often. OBD scan with jumper clip at port reads code 43 consistently now. Peeled back wiring harness from firewall to distributor and to injectors. No obvious issues, all wiring well insulated and connectors looked solid/clean. Have moved all connections and wiring harnesses to try to induce stall or injector clicking, no joy. Pulled ECM, inspected wire harness from ECM to f/wall, no obvious issues.

After all this, two consistent issues are repeating now.
1. Fuel injector clicking intermittently after stall, with key on.
2. During OBD scan, if I allow system to run through loop, injector will begin to click intermittently and CEL will flicker, interrupting scan process.

Any advice/help is appreciated.

 

[Chewy1576]

Did you replace the ICM with the distributor? When mine went bad, it would start and idle fine when cold, but as the engine got warmer and the ICM heated up it would run progressively worse until it would just die. Couldn't be started again until it had cooled off. Make sure to use heatsink compound when installing it in the distributor. If you use dielectric grease, you'll cook the new one too on the first startup.

 

[evilunclegrimace]

check the connection at the ESC module, at the Knock sensor and check the wire from the ESC connector Terminal C to ECM connector B7

 

[68Chev]

Yes, r/r'd spark control module next to MAP early on t/shooting, and swapped orig back in, no joy. Swapped out ICM prior to replacing distributor, no joy. Distributor was worn out, so it got r/r, came w/ new ICM.

Per Unclegrimace, will go through ICM and SCM wiring again. During all this t/s, I left clip in OBD port and started truck a time or two, which prob is a bad thing.

2 q's:

1. Would bad ground at fuel pump, (which was prob bad awhile), cause fuel pump relay to fail? Understand bad fuel pump ground could have had other neg effects on elec system. Does that relay have any effect on injector pulse issue described in first post?
2. Would leaving clip in OBD at motor startup fry modules like ICM spark control mod, PCM? May have done more damage with that bonehead mistake.

Side note - was looking for ICM heatsink compound at parts store and they told me to use dielectric grease or white lithium grease. Have read much blogging on this issue, but will stick with heatsink compound since that is what new ICM is supplied with.

Thanks all for assist.

 

[Schurkey]

89 Chevy K2500 4x4, 350 TBI, TH400 transmission. 250K miles

OBD scan with jumper clip at port reads code 43 consistently now.

That's not a "scan", that's "code reading".

I would want to connect a proper scan tool, so I could look at the data stream.

I'd also want to know--and follow--the full GM diagnostic procedure for code 43.

Peeled back wiring harness from firewall to distributor and to injectors. No obvious issues, all wiring well insulated and connectors looked solid/clean. Have moved all connections and wiring harnesses to try to induce stall or injector clicking, no joy. Pulled ECM, inspected wire harness from ECM to f/wall, no obvious issues.

After all this, two consistent issues are repeating now.
1. Fuel injector clicking intermittently after stall, with key on.
2. During OBD scan, if I allow system to run through loop, injector will begin to click intermittently and CEL will flicker, interrupting scan process.

The injectors should not fire if the ECM is not getting signal from the pickup coil through the ignition module, and on to the ECM.
1. Failed pickup coil
2. Failed ignition module
3. Failed wire harness
4. Failed ECM

The vehicle supplies power to the injectors whenever the key is "On" or "Crank". The injectors fire when the ECM provides ground. If the wire harness is grounding, you'd interfere with the proper firing of the injectors, and the injectors would fire whenever the harness grounded.

However, the intermittent and semi-regular nature of this fault makes me suspect the ECM.

I'd diagnose Code 43 first, and see what happens. If there's still stalling or injector firing when the engine is not running, I'd be looking at the harness again, and then pricing out a new ECM.

 

[68Chev]

Yes, just reading codes, don't have scanner or factory pubs. Anyone know what amp rating the fuel pump relay at firewall is, 15 or 30 amp?

Was doing other t/shooting and I forgot to install fuel pump relay at firewall. Truck ran great, no stall or misfires. May have bad relay, but I expected it not to run at all w/out the relay installed. I know the relay can be jumped direct to fuel pump to test it, but I didn't have it jumped either.

Thanks for the help.

 

[Schurkey]

The truck will run just fine without a fuel pump relay. The only problems it causes are 1) lack of 2-second "prime" when ignition is turned on, and 2) extended cranking time before engine starts. Engine has to crank long enough to build oil pressure before fuel pump will run.

The oil pressure switch ALSO powers the fuel pump, the load is shared by the oil switch and the pump relay. If either one is faulty, the other will carry the full electrical load.

 

[68Chev]

Thx for info Schurkey. Will continue t/shooting ECM and wiring. ECM you refer to is computer under glove box - correct?

1. If fuel pump relay removal eliminates misfire/stall, would that indicate possible short in relay? Did not notice crank time taking longer, will do longer test run tomorrow. Didn't want to induce a problem w/out knowing if relay was essential.

2. If I reinstall fuel press relay and disconnect oil pressure switch, run truck, and stall/misfire returns, would that indicate an issue w/ an elec component other than fuel press relay or oil press switch, or would it indicate bad oil press switch? Oil pressure switch you refer to is behind distributor - correct?

I replaced oil press switch about 2 yrs ago while working to fix same issue, along w/ plugs/wires/rotor/dist cap. Used aftermarket oil press switch tho. Oil pressure has been healthy per stock gauge in dash.

Also learned ECM (under glove box) is not OE. Replaced many yrs ago. Had it out to reinspect wiring and discovered I have the heavy duty model 2500 with a fuel pump control module on the rack under the PCM. Any idea what that components' purpose is?

Thx again for assist.

 

[Schurkey]

ECM you refer to is computer under glove box - correct?

Yes.

1. If fuel pump relay removal eliminates misfire/stall, would that indicate possible short in relay? Did not notice crank time taking longer, will do longer test run tomorrow. Didn't want to induce a problem w/out knowing if relay was essential.

I will be REALLY surprised if the fuel pump relay has anything to do with the misfire/stall.

2. If I reinstall fuel press relay and disconnect oil pressure switch, run truck, and stall/misfire returns, would that indicate an issue w/ an elec component other than fuel press relay or oil press switch, or would it indicate bad oil press switch? Oil pressure switch you refer to is behind distributor - correct?

If the stall/misfire comes back when the relay is installed and the oil switch disconnected, the oil switch and wiring is not at fault. The relay and/or relay wiring might be.

Yes, the oil pressure switch is behind/beside the distributor (at least on my truck.)

I replaced oil press switch about 2 yrs ago while working to fix same issue, along w/ plugs/wires/rotor/dist cap. Used aftermarket oil press switch tho. Oil pressure has been healthy per stock gauge in dash.

On my truck, the switch for the fuel pump is totally separate from the sending unit for the gauge. Sending unit for gauge is on block casting above oil filter.

Also learned ECM (under glove box) is not OE. Replaced many yrs ago. Had it out to reinspect wiring and discovered I have the heavy duty model 2500 with a fuel pump control module on the rack under the PCM. Any idea what that components' purpose is?

I don't know what the fuel pump control module is.

One wonders if it regulates voltage to the pump based on engine load or RPM, in which case if it's faulty--or getting faulty information from some sensor--you could have fuel pressure problems that might include stalling or misfire.

 

[68Chev]

Thx again Shurkey.

Fuel pump control module is unique to HD models from what I've learned. Pic attached. Mounted under ECM rack, still figuring out what function is.

Anyone know of a reliable source for ECM repair/rtn and programming for these old trucks, (besides bone yard)? Will post q in general electrical forum. I can find many replacements online, but I'd rather test mine before I replace, if I get to that point.

I have same setup w/ oil pressure switch at distributor, and oil press sensor for dash gauge at oil filter housing.

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