4.0 Liter Problems

C

Co-Man-Che

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Last Sunday I decided to remove the air conditioning and charcoal cannister from my Comanche and when I was done the truck wouldn't start. Cranks over, has spark, plugs are wet, 38 psi fuel pressure, swapped in a used crank position sensor, replaced the charcoal cannister, tried a different computer from a 5spd vehicle (mine is an automatic), checked fuses under hood and nothing has worked. If I let it sit for a few hours then try to start it, it acts like its about to start then just keeps cranking. When I was removing the AC my wrench made contact between the compressor and the positive terminal on the battery and it made a pretty good arc, could this have fried something? Do I need to try a computer from an automatic? Or is there something else I'm missing?

The truck is an '88 but the motor and entire wiring harness are from a 92 Cherokee.
 
4.0 Liters just die for no particular reason when they get old. The CPS is one of the more common reasons. But it could be almost any of the sensors.

But was it running IMMEDIATELY prior to the work you did? And if so, you said you removed the Air Conditioning. How did you re-route the serpentine belt? Did you pull a vacume line when removing the Charcoal Canister, and now have a significant vacume leak?
 
TreeClimber said:
4.0 Liters just die for no particular reason when they get old. The CPS is one of the more common reasons. But it could be almost any of the sensors.

But was it running IMMEDIATELY prior to the work you did? And if so, you said you removed the Air Conditioning. How did you re-route the serpentine belt? Did you pull a vacume line when removing the Charcoal Canister, and now have a significant vacume leak?
Click to expand...

I drove the truck into the shop right before I did the work. I left the compressor for the Ac on the motor because I plan on doing onboard air, but I removed the lines and the drier. The only vacuum line going to the charcoal cannister also went to the intake manifold and I blocked that off.
 
wazz said:
How did you check for spark?

The charcoal can system is good for the truck you might want to leave it in there.
Click to expand...

I checked for spark by pulling two plugs and setting them on the valve cover and cranking the motor over.

Why is the charcoal cannister good? I thought it was just there to catch fumes from the fuel tank. I wanted to remove it to make extra room under the hood and reduce some of the misc. hoses.
 
Did you check your relays?

I had a similar problem with my jeep 2.5 it would turn over and turn over but no fire, also had spark and fuel. took it to my uncle who was a mechanic and said it was just a stupid relay which was like 5 bucks. Wish i knew exactly which one but he did not tell me.
 
Couple of thoughts:

1) Engine ground. Make sure you didn't remove an engine to frame or engine to body ground wire along with the AC compressor stuff.

2) On some jeeps there are a TON of electrical plugs and sensors attached to the evap canaster and adjacent plumbing. Unplugging all that can't be good.

3) Hook it all back up and then remove it one connector at a time while confirming your truck runs in between your "un-plugs". No need to hard bolt everything back up; just bailing wire it safe enough to start.

4) Your short might have smoked a fusable link. They are designed to melt the wire inside without melting the insulation. On quick glance you might not see the burn't wire.

5) Clear your fault codes and scan again. Let the ECM diagnostics give you clues as to what's wrong.
 
slednecks1124 said:
Did you check your relays?

I had a similar problem with my jeep 2.5 it would turn over and turn over but no fire, also had spark and fuel. took it to my uncle who was a mechanic and said it was just a stupid relay which was like 5 bucks. Wish i knew exactly which one but he did not tell me.
Click to expand...

Without buying all new relays and replacing them one by one, how would I check the relays?
 
TigTorch said:
Couple of thoughts:

1) Engine ground. Make sure you didn't remove an engine to frame or engine to body ground wire along with the AC compressor stuff.

2) On some jeeps there are a TON of electrical plugs and sensors attached to the evap canaster and adjacent plumbing. Unplugging all that can't be good.

3) Hook it all back up and then remove it one connector at a time while confirming your truck runs in between your "un-plugs". No need to hard bolt everything back up; just bailing wire it safe enough to start.

4) Your short might have smoked a fusable link. They are designed to melt the wire inside without melting the insulation. On quick glance you might not see the burn't wire.

5) Clear your fault codes and scan again. Let the ECM diagnostics give you clues as to what's wrong.
Click to expand...


There was only one plug going to the evap can and I already tried plugging it back in. I'll check the engine ground and codes though.
 
If you have a new one you can switch it out with others and try to start it. if it does not work put the old one back in and continue on to other relays.

also check the things the guy before me said, just start narrowing down the possible problems.
 
I was just getting at the CC-can robs no power from the motor, and removing it "can" cause some weird problems, the fumes really want some way to expand when its hot outside.

Wet plugs, typically come down to weak or no spark,

or a raw fuel leak into the intake like a fuel psi reg. leaking fuel into it's vacuum hose (but that usualy runs just runs really bad).

You did you maybe mess up the firing order?
 
wazz said:
I was just getting at the CC-can robs no power from the motor, and removing it "can" cause some weird problems, the fumes really want some way to expand when its hot outside.

Wet plugs, typically come down to weak or no spark,

or a raw fuel leak into the intake like a fuel psi reg. leaking fuel into it's vacuum hose (but that usualy runs just runs really bad).

You did you maybe mess up the firing order?
Click to expand...

I don't know how I would have messed up the firing order, never messed with the plug wires. It's not even backfiring either.
 
Checked engine grounds, checked relays, swapped in a coil and distributor that are known to be good, tried to pull codes-nothing came up. This thing still won't run. Any other ideas?
 
4.0's have a couple of sensors that will cause a no-start, CPS is one but often overlooked is the TPS.

Now I'm sure we're all tracking that removeing the Evap can by itself shouldn't cause a no-start but there's always the chance you dislodged something or leaned against a connector or...something.
 

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