New to GMT400 from Oregon

[g00se]

Hello, I recently picked up a 1994 5.7 5 speed manual 5.7L 2500 truck. I've always wanted one of these and just now getting acquainted. I've been browsing this forum for a while which has been great!

The truck runs and drives pretty good --but won't pass emission testing. It first failed for CO and HC (it smelled a little rich). I replaced the coolant temperature sensor and MAP sensor and air filter. It passed for CO on the second test --but still failed for HC. It had no OBDI check engine light errors.

I replaced the spark plugs and wires, cap and rotor and it seems to be running better and I drove it around awhile and decided to take it in for a third test --but it threw a CEL on the way so I turned back home to check the codes. It has a DTC 15 (coolant sensor), DTC 32 (EGR) and DTC 54 (fuel pump relay?)

That DTC 54 seems unrelated to the HC emissions fail. The DTC 32 could be the EGR solenoid? My EGR solenoid has three wires in a four wire connector. I'm hoping I can test it with multimeter --probably the same with the DTC 15 coolant sensor.?

I really like this truck and really appreciate any help figuring out what to do next.

 

[PlayingWithTBI]

Welcome, What part of Oregon are you from? We used to have a ranch on State Line Hwy in Merrill 24 miles North of Klamath Falls.

I think you're on the right path, Co & HC is usually just a tuneup and, if your TPS was bad it may run rich due to it's thinking your engine is cold. The EGR was developed for NOx so, that probably won't contribute but, you need to correct the codes. Did you by any chance unhook the vacuum line going to the EGR valve and maybe connect it to the wrong port on the solenoid? Or maybe got a loose connection when you changed out the TPS? Are your grounds on the T-Stat clean and tight? Those are the grounds going to the PCM. Check those out and disconnect the battery to reset the PCM and drive it for a while so it warms up and starts modulating the EGR to see if it throws a code again.

 

[frito-bandito]

Welcome to the forum!

 

[F4U-1A]

The dreaded E test, when we had (money grab gone now) it, if your vehicle was 25yrs old no test was required. Theory being, that old and still around (salt). it would be next to impossible to pass. Good Luck and welcome.

 

[g00se]

Thanks guys! I appreciate it!

I will double check the vacuum lines --if I remember correctly, the EGR solenoid had two different size lines --the larger one went to the TBI and the smaller diameter went to the EGR valve --I'll look to see if I put them on the wrong solenoid fittings. I did pop the 'filter' cap off the EGR solenoid and it was there and intact. Very dusty but it wasn't dried out or missing.

I'll check that ground by the thermostat and ECT sensor and make sure it's good. I'll also Ohm test the new sensor.

I think I can ohm test the EGR solenoid if I test the outer two leads (4 position connector)--power and ground. If it's open than the internal coil of the solenoid is bad..? and that is triggering the DTC 32..?

When I was searching for OBD1 error codes --it came up with options for that DTC 54 which was 'fuel pump relay' but also had an EGR related error. I'm hoping that these all are pointing towards the same cause ---because it seems to be running real well.

@PlayingWithTBI, I'm from the Hillsboro/Aloha/Beaverton area --more north than K-falls. That is a real pretty area, very scenic! I will disconnect the battery to clear the codes and see if they come back on. One other thing that I think is completely unrelated is that when the check engine light came on --the turn signal relay fell out from under the dash and was hanging near the clutch. It was a round can with two wires --I think it was just tucked up near the fuse box and fell out. I tucked it back --will have a closer look today --zip tie it in place

@F4U-1A, I was hoping that after 25 years it would not need to be tested either. I guess that isn't true in Oregon... I was looking into an 'SP' (special purpose?) plate but it turns out that it is only for car-show limited driving vehicles. I don't think my (new to me) C2500 would be accepted. I like it --runs and drives nice --no rust but a few dings a work truck would have after a long life of service. Stock exhaust but I love the sound of it starting up..

 

[PlayingWithTBI]

if I remember correctly, the EGR solenoid had two different size lines --the larger one went to the TBI and the smaller diameter went to the EGR valve

The one that goes to the valve itself goes on one port and the other is a vent (above it IIRC). Make sure you have it on the correct port. Here's the routing diagram from my 88.

You must be registered for see images attach

 

[Stumpy]

Welcome g00se.

 

[Wh4t3v3rs]

Just throwing this out there.... I have a 95 and I fought with drivability and my problem was all the hard plastic vacuum lines were leaking where the hard line connected with the rubber. I put a little sealant on before I put the rubber connectors and it solved my problems..... I know, that would be to easy!!! Might double check!

Anyways, welcome to the forum and good luck!!!

 

[g00se]

I haven't been able to get back to my truck all week.

But I have checked the vacuum lines going to the EGR and solenoid. They look to be hooked up correctly. On mine (94) it has two ports on the same side --one large and one smaller. The other port is actually capped with a foam filter (I'll take some pics and post). That doesn't really match the emission hose schematic..

I did pull the ground cable connection from near the thermostat and cleaned it up. It was covered with dust and grime --this truck has seen a lot of dirt!!

I've cleared the 'check engine' light codes by disconnecting the battery (also cleaned the terminal connection). I'll try to get some time on it today.

@Wh4t3v3rs, I will check those hard lines --maybe add some sealant just in case. The rubber part was pretty tough to wiggle off the ports.

@Stumpy, @frito-bandito,Thanks!!

 

[g00se]

Just a quick update, since I cleared the codes they have not returned. I drove it around to get it good and warmed up. I checked and set the timing (it was a little off). --I also sprayed some WD-40 on the vacuum lines but it didn't seem to make a difference in how it was idling (seems to idle smooth/normal).

It still smells like it is running rich... was hoping after tuning it would do better. I haven't taken it in for another emission test yet. But no codes now --so not sure what to check next. Maybe just change out the EGR solenoid and the EGR valve --but wondering if the injectors need cleaned. I've heard you can see the pattern better if you use a timing light --so I'll try that out. Seems to be running good --but guessing that rich smell is a sign that it will fail the emission testing.