CEL triggers only while cruising

[Madison Mehlhose]

1989 K1500 RCLB 5.7 TBI

The only components that aren't new are EGR vavle, ECM, ESC module, fuel pump, and MAP sensor. I will be checking the MAP sensor and fuel pressure today.
Has shorty headers with true dual. Fresh top end gasket job (no leaks).

The truck runs great, idles like a dream, however, it doesn't have as much power as I think it should, could be an illusion thou.

While cruising for about 30s to a minute at any speed, the truck will trigger a code 13. Running around town it wont trigger and will actually turn off the light shortly after I stop cruising.

Anyone have any ideas?

 

[jkeaton]

This might help.

http://www.gmt400.com/threads/95-gmc-obd1-code-13.17439/

 

[Madison Mehlhose]

I don't want to do the switch from 1 wire to 3.
Also, i tried measuring the voltage from the HARNESS to Ground and it reads 1.48V. According to the flowchart either an open ground or i need a new ECM... i checked the ground and its good.
I haven't seen any threads on this site end with replacing the ECM, so you can see my skepticism.

 

[someotherguy]

These ECMs rarely, and I mean very rarely, are bad. So when chasing a problem you usually put it at the very bottom of the list, if at all.

Having free-flowing exhaust, and going true duals on a truck that only has 1 O2 sensor...is a handicap to the system. A great solution would be an H pipe with the O2 bung right there and a heated O2 sensor.

Richard

 

[Madison Mehlhose]

Any ideas on the harness being over voltage?
Also, i forgot to mention that the plugs looked really lean. I suspect im not getting enough fuel or too much air.

 

[Madison Mehlhose]

How would a heated plug fix my issue anyways? From what i understand it will only tell me that the air fuel mixture is incorrect sooner as it has its own heating circuit.

 

[someotherguy]

The non-heated sensor uses exhaust heat to reach "light off" temperature* and begin generating a signal. Without sufficient heat (free flowing exhaust or improper placement) it cannot work.

Richard

* edit - about 600F by the way.

 

[NightRunner]

Take this with a grain of salt as I haven't been driving my truck as much since I got it but did notice the exact same issue. It didn't happen until last night after changing the manifolds out for long tubes without an O2 sensor in place. So I'd be willing to wager that your O2 sensor is biting the dust. Personally I have no use for it since I'm either tuning it out or going carb and eliminating the computer entirely in the future. Lol

 

[Madison Mehlhose]

I agree with what your saying someotherguy but i'm skeptical that my exhaust isn't reaching 600+ degrees. When I first noticed it, I was driving down the highway at 80mph pushing 2100 rpms. Surely that is enough exhaust gas to reach 600F. I do have headers, true dual with no cats but I know that a stock 'restrictive' setup wont change the composition of the gas, merely only the pressure and therefor temperature. I'll try the heated sensor tomorrow but I think there is an underlying issue.

Can someone go probe their truck with a multi-meter [key on engine off] and tell me that reading ~1.48v from the O2 harness side to ground isn't crazy?

 

[grampadirt]

These ECMs rarely, and I mean very rarely, are bad. So when chasing a problem you usually put it at the very bottom of the list, if at all.

Having free-flowing exhaust, and going true duals on a truck that only has 1 O2 sensor...is a handicap to the system. A great solution would be an H pipe with the O2 bung right there and a heated O2 sensor.

Richard

I was contemplating doing that very thing since the ECM would need to read the exhaust from both banks and having a heated o2 sensor would accomplish that task.I was thinking long tube headers and thought to mount the sensor after the collectors so far away from the engine a one wire sensor would never heat up enough,might stay in open loop.