The Stupid Engine Questions Thread

[PlayingWithTBI]

Am I on the right track?

You can try it, data logging is always a good thing when you're looking for issues with sensors, and outputs, etc. Data Logging won't tell you if you have other hardware or wiring issues. Those, you'll have to find but, it may point you in the right direction. Enjoy!

 

[FourEightZero]

So, I'm headed to the shop today to further investigate.

Gonna disconnect the battery to clear the memory and get some fresh readings in TunerPro.

The three problem parameters I'm seeing are the fuel trims climbing up to around 135-140 and my knock retard hovering around 24° (I'm not seeing the knock counter climb.. but there is 120 something counts)

NBO2 sensor is a new single wire Bosch and it appears to have normal readings in closed loop.

The engine is stumbling (possible misfire?) and when I let it idle it eventually dies. Same behavior whether it's warm or cold.

It's a rebuilt engine with only 200 miles on it and it ran flawlessly until I started having what appears to be electrical issues.

Any ideas?

 

[kenh]

So, I'm headed to the shop today to further investigate.

Gonna disconnect the battery to clear the memory and get some fresh readings in TunerPro.

The three problem parameters I'm seeing are the fuel trims climbing up to around 135-140 and my knock retard hovering around 24° (I'm not seeing the knock counter climb.. but there is 120 something counts)

NBO2 sensor is a new single wire Bosch and it appears to have normal readings in closed loop.

The engine is stumbling (possible misfire?) and when I let it idle it eventually dies. Same behavior whether it's warm or cold.

It's a rebuilt engine with only 200 miles on it and it ran flawlessly until I started having what appears to be electrical issues.

Any ideas?

Grounds are super important. Clean and tight. IMO it's not good enough to rely on the bolt threads. Clean the surface the ground is attached to, to bare metal. Maybe a coil that is flakey or ignition module. I assume you replaced the cap, rotor and wires???

ken

 

[FourEightZero]

Grounds are super important. Clean and tight. IMO it's not good enough to rely on the bolt threads. Clean the surface the ground is attached to, to bare metal. Maybe a coil that is flakey or ignition module. I assume you replaced the cap, rotor and wires???

ken

Yes. Aside from the block, crank, and possibly the rods (had machine shop do the whole bottom end) everything on this engine is brand new.

Cardone distributor (whole thing), NGK coil, new wires and plugs (can't remember brands).

 

[FourEightZero]

So, I have had an ICM OBD1 code in the past and given that these modules are an achilles heel and I'm suspecting an electrical/electroinc issue is causing this misfiring, I pulled it to go get tested.

I have no codes atm, but I have disconnected the battery several times since this issue started.

On the 4-pin connector I noticed this. I'm assuming a new connector is due.

Update: ICM is good. DIYer manager was telling me about watching under the hood while idling when it's dark and looking for arcing. I saw this a few months ago.

I'm assuming this 30 year old wiring all over the truck is to blame.

 

[FourEightZero]

So, I have had an ICM OBD1 code in the past and given that these modules are an achilles heel and I'm suspecting an electrical/electroinc issue is causing this misfiring, I pulled it to go get tested.

I have no codes atm, but I have disconnected the battery several times since this issue started.

On the 4-pin connector I noticed this. I'm assuming a new connector is due.

Update: ICM is good. DIYer manager was telling me about watching under the hood while idling when it's dark and looking for arcing. I saw this a few months ago.

I'm assuming this 30 year old wiring all over the truck is to blame.

Spliced in the new 4-pin ignition control module connector and my fuel trims corrected to 128/128. Knock retard is still high and truck is idling at 580-590, but it's not dying. Sounds like the misfire is gone.

Snapshot before I wrapped it up for the night.

 

[Komet]

What load leveler or similar type item is good for plucking an L31 out of a truck? I have the hoist already but I still need the part that attaches to the engine.

 

[Erik the Awful]

A lot of people don't like these, but I've used one for years and I don't like swapping engines without the ability to tilt it when I need to. Mine's not Harbor Freight, but it looks like it was made on the same assembly line.

3/4 ton Capacity Load Leveler

Amazing deals on this 3/4T Load Leveler at Harbor Freight. Quality tools & low prices.

www.harborfreight.com

SAFETY ALERT! Do not use your hands to turn the screw. ALWAYS use a ratchet. Years ago I had to tilt my motor just a little more. The load shifted and it pinched me between my thumb and hand. I lost a big chunk of skin and a fair amount of blood before I got it handled.

The downside of using one is the extra height it adds to your crane. You'll either need to pull your core support or you'll have to pull your hood and take the wheels off your truck to get the nose down near the ground.

 

[cakyman]

Hey does anyone know what this connector is for? 94 305, I know I bought the truck with the EGR solenoid pulled, but i cant for the life of me figure out what this connector goes to.

 

[Menissalt]

I've got a squeak when starting and I don't know what's causing it, it's shorter when warm but still there. Had the belt changed a couple hundred miles ago but that didn't change anything.

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