90 350 service engine soon flashing while running

[munrom77]

Hello all,

Little but stumped right now with my truck, I recently installed a freshened up 350 has 150 compression across the board, has all new sensors and plugs wires etc,

Recently set my timing with the wire unplugged to 0 or very close to it, shut down the truck plugged the wire back in seems to run ok did a check with the timing light again and found it’s still sitting at 0 I thought once plugged in it should go to around 10 degrees or so. It seems to run ok so far for just running it up in park and letting it idle, had a bit of a hesitation when letting off the throttle but not terrible.

I go to get the blink codes out of the truck and the light goes to die out half way through the blink procedure or the light gets very dim.

So couple questions I would like some help with. I have done some reading and I’m almost lead to believe I may have an issue with my ecm, I do not know how an engine ran in this truck before as I bought it as a rolling chassis.


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[evilunclegrimace]

A little more info would help. Year, make, model. Check all ground and connections. All of my '88,'90 and '92's run some where around 25-28 degrees with the EST by pass plugged in after setting base timing to zero degrees.

OOPS sorry I just got off work and am a bit frazzled I reread the Op's post and see that it is a '90 truck, My bad

 

[munrom77]

It’s a 1990 gmc k1500 with a stock 350


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[evilunclegrimace]

It’s a 1990 gmc k1500 with a stock 350


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Yea I corrected my post Sorry,

 

[munrom77]

So I tried to get blink codes this morning again after the 3 1-2 combo I got 5-1-4-1-3 and the three really faded out that you could just see it and have good 12.6 volts when doing it


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[evilunclegrimace]

There are not enough numbers to tell what the problem is. All of the flash codes are 2 digit number combos. So, IF your first code is 51 that indicates a faulty MEM-CAL, PROM, or ECM. There is not a 41 code, and a thirteen code is a bad O2 sensor. BUT! The codes should flash is ascending order if I remember correctly 12,13,14, 24, 35 etc.

A quick check is to clear all of the codes and see if the ECM can recognize a forced code. Try unplugging the TPS and see if the ECM throws a code for a TPS low voltage. if it can not recognize a forced code the ECM could be faulty.

Your best bet is to connect a scanner to the truck and run some diagnostics with the scanner and recheck for codes.

 

[PlayingWithTBI]

Check all ground and connections.

^^^X2 - especially the 2 grounds that go next to the T-Stat housing, those are for your ECM. Then you have battery to fender, battery to block, block to frame, and the one that most people forget to put back after a swap, back of the passenger head to the firewall.

Your best bet is to connect a scanner to the truck and run some diagnostics with the scanner and recheck for codes.

^^^X2

 

[munrom77]

^^^X2 - especially the 2 grounds that go next to the T-Stat housing, those are for your ECM. Then you have battery to fender, battery to block, block to frame, and the one that most people forget to put back after a swap, back of the passenger head to the firewall.


^^^X2

All grounds are all new for battery to block ,battery to cab, frame to cab, battery to frame. I will check all the grounds at the thermostat and double check my work and am looking for a scan tool that has obd1 ability all of mine that I have are not able to do obd1


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[Schurkey]

1. Screw the "blink codes". You need to connect a scan tool to get codes AND the data stream.

2. If you've got no history with this truck, and the engine is fresh, CLEAR ALL THE CODES and see what comes back. AGAIN, the data stream means at least as much as the "codes".

3. If the MIL is flashing on and off, don't drive the truck. A flashing MIL means the catalyst is in serious danger; you could melt it by continuing to run the engine.

 

[munrom77]

1. Screw the "blink codes". You need to connect a scan tool to get codes AND the data stream.

2. If you've got no history with this truck, and the engine is fresh, CLEAR ALL THE CODES and see what comes back. AGAIN, the data stream means at least as much as the "codes".

3. If the MIL is flashing on and off, don't drive the truck. A flashing MIL means the catalyst is in serious danger; you could melt it by continuing to run the engine.

Catalyst? I assume you mean cat converter? This truck doesn’t have it and is not required to have it, it has stock manifolds (new) new y pipe, 3 in to the muffler and dual 2.5 out to the tail pipes


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