'91 Chevy 4x4 electrical problems...

[Hammack_Welding]

Guys I have a '91 chevy 4x4 that has been giving me fits. I was running down the road the other day and the gauges started going crazy. ( flipping back and forth or pegging out) The truck seemed to lose power, but was still driveable. I made it the 4-5 miles back home. after getting back it got where it would turn fine, but would not crank. Today after some inspection, I noticed my starter solenoid had a part broken out of it so I pulled the starter, and replaced the solenoid. There was also a few wires that were cracked etc. (mainly 4x4 wires) and she started right up, and drove down the road. A half mile later it starts the same thing again. Sounds like the engine has a load on it, and while it is running now the volt meter shows about 11 volts, but when checked at the battery it shows the altenator is charging fine. Any suggestions on where to look now are GREATLY APPRECIATED! I need this thing up and running by the end of the week for a job I have scheduled. :confused:

[duaneb55]

First thought - fusable link at starter feeding electrical system?

. . .or corroded/burned connection(s) at fuse block/wire harness connector on firewall?

I'm still thinkin'. . .

[Magnetic Mechanic]

"The truck seemed to lose power, but was still driveable"

That distributor has a limp mode function that locks the timing at TDC if you experience ignition input failure. Sounds like you are there.

Put a jumper in the A and B slots on the ALDL to ground the diagnostic terminal and trouble codes will flash on the dash when you turn on the ignition. Each code will flash (i think) 3 times then go to the next code. Keep reading till codes repeat.

code - code definition
12- diagnostic mode
13- 02 sensor or circuit
14- coolant sensor or circuit/ high temp indicated
15- coolant sensor or circuit/ low temp indicated
16- system voltage out of range
19- crankshaft position sensor or circuit
21- throttle position sensor or circuit- voltage high
22- throttle position sensor or circuit- voltage low
23- mixture control (m/c) solenoid or circuit (carbureted models)
23- manifold air temperature (mat) sensor or circuit (1990 and earlier models) 23- intake air temperature (iat) sensor circuit (fuel-injected models)
24- vehicle speed sensor (vss) or circuit
25- manifold air temperature (mat) sensor or circuit - high temperature indicated (1990 and earlier models)
25- intake air temperature (iat) sensor or circuit - high temperature indicated (1991 and later models)
26- quad driver module circuit
27- quad driver module circuit
28- quad driver module circuit
29- quad driver module circuit
31- park/neutral position (pnp) switch circuit
32- baro sensor or circuit (carbureted models)
32- egr circuit (fuel-injected models)
33- manifold absolute pressure (map sensor signal voltage high
33- mass air flow (maf) sensor or circuit - excessive airflow indicated
34- manifold absolute pressure (map) sensor signal voltage low
34- mass air flow (maf) sensor signal - low airflow indicated
35- idle speed control (isc) switch or circuit (shorted) (carbureted models)
35- idle air control (iac) valve/ circuit
38- brake switch circuit
39- torque converter clutch (tcc) circuit
41- no distributor signals to ecm, or faulty ignition module ( carbed models)
41- cylinders select error- mem-cal or ecm problem ( fuel-injected models
41- cam sensor circuit (3.8 engine)
42- bypass or electronic spark timing (est) circuit
43- low voltage at ecm terminal l (carbureted models)
43- knock sensor circuit
44- oxygen sensor or circuit - lean exhaust detected
45- oxygen sensor or circuit - rich exhaust detected
46- power steering pressure switch circuit
48- misfire diagnosis
51- prom, mem-cal or ecm problem
52- calpak or ecm problem
53- egr fault (carbureted models only)
53- system over-voltage (ecm over 17.7 volts)
54- mixture control (m/c) solenoid or circuit (carbureted models)
54- fuel pump circuit (1986 and later models)
55- oxygen sensor circuit or ecm
55- fuel lean monitor (2.2l engine)
61- oxygen sensor signal faulty (possible contaminated sensor)
62- transaxle gear switch signal circuits
63- manifold absolute pressure (map) sensor voltage high (low vacuum detected)
64- manifold absolute pressure (map) sensor voltage low (high vacuum detected)
66- pressure sensor or circuit air conditioning

[Hammack_Welding]

Thanks, I will check that tomorrow!

[transit]

One more thought, after witting the error codes down. Disconnect both battery cables to reset the ALD. Reconnect the battery, drive and see if any new codes show up.

[denrep]

...while it is running now the volt meter shows about 11 volts, but when checked at the battery it shows the altenator is charging fine....

That makes me suspect that the body or chassis ground is open, and current is taking a stray return path.

Quick test with your jumper cables: Connect two clamps to the negative terminal of the battery, then the other two clamps; connect one to the body, and the other to the frame.

Good Luck

[Atomik777]

Sounds like a short on the line from the starter to the battery

[denrep]

What'd she say, boss?

[David R]

I am pretty sure you have a bad wire some place. A poor ground, a poor hot connection, a small control wire with a "green" spot in it. I run into these occasionally. Its a bear to find. You can check connectors for green terminals. I would check power in and ground for the computer.

Its NOT a short between the battery and starter or you wold have instant smoke.

Intermittent problems suck.

A toasted wire to the ign switch?

Are all the wires going to the starter CLEAN at the connections?

Are the main ground wire and + wire all in good shape? No green stuff at the ends?

Battery terminals clean?

Hot wire form the alt to the junction box in good shape?

You could pull out the power distribution box and look in from the bottom for corrosion (more green stuff)

A poor connectioin would make the guages jump back and forth like you turned it off and on, so Its probably in the heavier circuits.

"runs like crap" is a symptom, not a problem.

Codes may point you towards the problem, but may be misleading because you do have low voltage at times. If you do get a code, please post it here. Some are important some are useless.

Check for 5 volt reference on the Throttle position sensor, or Map sensor and a good ground for both. This will tell you if one item (any thing) is draining down your 5 volt reference or computer ground is bad. Each of those sensors have 3 wires. +5 volts, the output and ground.

You can have some one watch the gauges while its running (or not) and wiggle wires. This may narrow it down.

Wiggle the key while its running, watch the gauges......

There are connections on the passenger side inside the engine compartment on the fire wall. I have seen those corrode. This is where your alt wire meets up with some other heavy battery wires.

For sure its a poor connection some where.

Just a bunch of random thoughts. Good luck

David :)

[Hammack_Welding]

Thanks for the info guys, we are working on her today. So far I clean all starter ignition connections I can get to, and/or replaced cracked or damaged wires. Still pretty much the same. I went ahead and ran a new ground strap from engine to frame and from battery to the body plus cleaned other ground connections. I think it has to be a bad wire somewhere. We are going back out after lunch and started chasing wires. I'll post back this evening with what we come up with if anything. Thanks again for the help!

[David R]

Well Jackson, its 10:30 here, are you still out there working?

Sometimes I gotta walk away for a while. I do have a book on that truck at work with wiring diagrams.

Good luck

David :)

[tigmusky]

One more thing It's along shot. but, maybe... your alt. if it gos bad and put ac volts instead of dc it will make the emc or comp think it's on drugs!!! computers don't like ac voltage.
Daye

[Hammack_Welding]

we have been chasing wires for two days and found nothing bad. I even checked for continuity to ground with a meter thru most wires. the alt will be changed in the morning as it was replaced shortly before the problems started. i also have a spare computer to try tomorrow just in case.

[Hammack_Welding]

Still gotten no where. Crank the truck up and it will idle all day. Pull wires, nothing changes. turn on something to place a draw on the electrical system and the truck will die. when you switch the ignition on the temp gauge pegs out, and the rest don't register. Grab the truck and rock it back and forth and the gauges start flipping back and forth like a loose connection. Still looking, no progress. The battery load tests ok, and the alternator is new and reads 15v charging which is a bit high I thought but It hasn;t given me any trouble.

[denrep]

I'm still betting on an open ground.
While the ground is being meter-checked with the truck being stationary, the ground path could be being shared by some stray path, leading to a good reading; when the truck shakes the stray path opens.

Run a temporary ground from the bare metal stamping that supports the dash and steering column, directly to battery Neg, and see what happens.

Good Luck

[Hammack_Welding]

Denrep, you are correct. It was a bad ground. Where I have no clue, but we added two new additional ground straps from the engine to the frame, and two more from the body to the frame, and then a new ground from the body to the negative side of the battery. Problem solved. Thanks for the help everyone. Now if I can figure out how to get the dang air conditioning blower fan out of it I can finish everything on the list for this truck.

[denrep]

Good that you fixed it, because the barge operators are starting to complain a little, about some of the larger sunken metal they hit when passing under the bridge.

[Hammack_Welding]

Good that you fixed it, because the barge operators are starting to complain a little, about some of the larger sunken metal they hit when passing under the bridge.

Yea, another day, and it was gonna be there!!!:realmad: