Truck runs okay for the most part one day and awful the next. Yesterday it bogged down so bad it finally threw an EGR code, though I'd recently cleaned it. I reset the computer and it was fine after that. Today it did it again pulled the EGR and cleaned it of pretty much nothing and reinstalled.

One strange thing the truck has been doing is on start up its running very rich. I can smell the gas. Then when it switches between closed/open loop it stumbles badly and sound like it will stall.

Today I swapped out the ECU (though I am using the old memcal). I really hoped this would solve the problem. No luck. I also changed the Temp sending unit (ecu) is hopes it was the issue... but I needed one anyway, the plug was snapped and glued on.

No change in how it runs.


What's left?

 

Swapped memcal, no change.

 

Check the connector for the coolant sensor. You mentioned it was snapped off. When the engine is cold, (open loop) the PCM ignores data from the oxygen sensors and uses data from the coolant sensor, throttle position sensor, MAP sensor, etc for determining fuel mixture. When it switches to closed loop, (anywhere from 20 seconds to 20 minutes) the PCM mainly uses oxygen sensor data for monitoring and adjusting fuel mixture. The other sensors are still used in closed loop, but if the coolant sensor data is incorrect or missing, the PCM will richen the mixture. The easy way to check if the PCM is seeing ECT signal, is with a scan tool. If the connector is bad, either a boneyard or auto parts store will have one.

 

I replaced the ETC a couple weeks ago. The old one had the plastic snapped off, it still made a good connection but didn't lock on. (It locked on, but the piece it was locked too pulled off as well. It was all siliconed in place).

The only thing left that I can think of is the distributor. It's not new, but its not original. It's probably 5-6 years old. (The cap, rotor, module and pickup are new). I have a hard time accepting the fact that a bad distributor would only cause problems when I try to merge.

 

Yup, I doubt it's the distributor or it would act up all the time. It sounds like it acts up when switching to closed loop. That could indicate a problem with the oxygen sensors, or their circuits, or the ECT sensor, or its circuit. Did you check resistance from the black wire at the ECT connector to battery negative? Must be 5 ohms or less at all times.... try wiggling wires around when testing and look for irregularities in resistance.

 

Now that I've put my old parts back and since I changed the memcal it's "normalized". The only time I have a problem is taking off from a light , if I try to give it more throttle than she likes, or when I'm trying to merge into traffic which is where it's the biggest issue. She sputters and coughs, and will backfire if I keep on it. Otherwise it's running great, gas mileage is as it should be. The problem I described with funky starts and smelling gas when I started it seems to have gone away when I switched back the O2 sensor. I suspected that since that's about when that started and the reason I switched back.

What's so confusing is it did this (sputter thing) last year, exactly. I changed the spider and the fuel pump and it went away.


Remembering.. another thing that I changed two (?) years ago when I first changed the spider was the electrical connection/plug to it. I changed it because it was brittle and broke, but I've read of those giving people mystery fits. But again would something like that only do it under a certain load/rpm?