1989 C1500, EGR, Headers Question

[FullBlowncustoms]

When you turn the key on, engine off, does your SES light flash on/off once, then come on steady until you start the engine? If it does, the light bulb is good AND the ECM is working. Now we need to figure out what's wrong with your ALDL connector and wiring...

If I had to guess, something's wrong with your O2 sensor and when it goes into Closed Loop. Without a scanner, it'll be hard to diagnose

With a paper clip, or solid copper core wire in or out of the A and B terminals, key on in correct position the check gauge light just stays lit steady, and battery light also, no connection or flashes for codes.... 95 truck works correct though with connections, flashes etc...

 

[FullBlowncustoms]

When you turn the key on, engine off, does your SES light flash on/off once, then come on steady until you start the engine? If it does, the light bulb is good AND the ECM is working. Now we need to figure out what's wrong with your ALDL connector and wiring...

If I had to guess, something's wrong with your O2 sensor and when it goes into Closed Loop. Without a scanner, it'll be hard to diagnose

Why would a bad O2 sensor not even let the unit connect?

 

[PlayingWithTBI]

With a paper clip, or solid copper core wire in or out of the A and B terminals, key on in correct position the check gauge light just stays lit steady,

I meant without and jumpers, just turn the key on - sorry for the confusion.

Why would a bad O2 sensor not even let the unit connect?

I was referring to your issue(s) when hitting it once warm - again sorry for the confusion.

 

[FullBlowncustoms]

Next to the battery is like this shiny tin looking old style relay? the wires are on it but not connected, just tucked in. The ground battery terminal has the ground cable to the block, then other grounds to the chassis etc... but off the ground cable at battery a short like 10 gauge ground wire is cut off at end, like maybe it went to the fender? Next to the fuel relay is a orange or red wire with like a tiny 5amp fuse, that wire leads to this retractable maintenance lite next to the battery on the pass side fender. Looks like a stock unit. It lights up if ya turn the slider switch tab on it.

 

[Scooterwrench]

Yeah that's your reel light. I you pull the light socket out it's on a cord that allows you to use the light to illuminate something your working on. Mine has a long enough cord to reach the rear wheels. There is a little crank handle on it to wind the cord back in. Pretty cool device!

 

[PlayingWithTBI]

The ground battery terminal has the ground cable to the block, then other grounds to the chassis etc

Yes, big ground from battery to front of engine, front of engine to frame, back of passenger side head to fire wall stud (earlier models don't have a wire to frame back there but, it wouldn't hurt). Yes, small ground wire goes to fender.

Next to the fuel relay is a orange or red wire with like a tiny 5amp fuse, that wire leads to this retractable maintenance lite next to the battery on the pass side fender. Looks like a stock unit. It lights up if ya turn the slider switch tab on it.

Yeah that's your reel light. I you pull the light socket out it's on a cord that allows you to use the light to illuminate something your working on. Mine has a long enough cord to reach the rear wheels. There is a little crank handle on it to wind the cord back in. Pretty cool device!

^^^Yep, that fuse should feed your under hood light, if supplied, too.

 

[FullBlowncustoms]

So the oil pressure sensor and the coolant temp sensor BOTH use the puter telling it for fuel? and the oil one is a safety thing that kills it? NOT that I would do it now that I know the problem, but for future knowledge can the oil one be wire jumped with a loop like I did the coolant one for a test?

 

[Scooterwrench]

No. Oil pressure has nothing to do with fueling other than to keep the pump running. Fueling is controlled by ECT,TPS,MAP,MAF,IAT and O2 pretty much in that order in the msec time range. In closed loop the PCM is monitoring those sensors and making adjustments.
I believe the fuel pump side of the oil sensor is a redundant switch for the PCM.

 

[Schurkey]

So was that sensor all along, RAN GREAT for 2 hours though, until I really hit it at WOT

The oil pressure sensor is a bypass for the fuel pump relay.

If the truck runs differently when the oil pressure switch is disconnected, there's SOMETHING WRONG with the fuel pump relay or it's wiring.

The fuel pump should run just fine with the relay removed (running off the oil pressure switch.) The fuel pump should run just fine with the oil pressure switch disconnected (running off the relay.) EITHER system should run the vehicle. If you have connection problems at the oil switch, and it affects how the engine runs...you've ALSO got problems with the relay circuit--the relay itself, or the wire harness connecting to it.

The diagnostic A-B terminals still never get a connection to read the flashes, My 95 truck I tested and works fine. Not sure why, but it doesn't effect the performance any..

Time to pop the connectors at the computer, and perform continuity tests to the various pins on the diagnostic connector. SOMETHING is messed-up.

 

[92 Longbed]

So we have a little information but not really enough to be of any real help. For example, we know you have a new distributor, oil pressure sensor and coolant temp sensor. There are two of these, one for the gauge/light, one for the computer. Which did you replace?
How many miles on the engine? Does it have a stock TBI cam? Is the timing set properly at 0* BTDC? Look at the timing mark with the engine running at steady speeds, say, idle 1,500 and 2,500 RPM. Is the mark steady or jumping back and forth? What makes you think it is running lean?