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4.0 Liter Problems

}side note, arrr,,, my last 3 jobs have ended up with bad computers, (87 22REC, 90 Mazda 626, & 94 Escort, my only guess is the prolonged 20* weather, killed um > they all had very weird symptoms, (sucked to figure out).lol


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Some ideas that may help,,,
You will need dry plugs it to run, wet wont work.

Maybe a fuel sample would be a good idea.
You may have water in the gas tank.

Might try and disable the fuel pump and see if it runs on starting fluid, try to confirm it will run some how.
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On one that took me a weak to figure out, it turns out the wires INSIDE of the bulkhead connector for the wiring harness (to the fuse box) had fried. Basically, we'd traced the harness to the key, but couldn't get the power from the key to go back to the ignition portion of the engine... Once we figured out where the broken wire was, we just jumpered the bulkhead connector and it ran fine.

But common sense dictates that is the exception, rather than the rule, and it's more normal to start at the Crank Positon Sensor, and the fender-well relay.

Anyhow, there are only three things needed to make an engine run.
1 Spark at the correct time
2 Fuel and air, at the correct mixture (or close)
3 Compression

Eliminate the obvious, and do a compression test.
Then make sure you've got good fuel, instead of crappy gas/water/dirt etc. Replace the fuel filter(s) just for good measure. Retake the fuel pressure. Make sure the injectors are clean (NOT clogged, a stream of gas doesn't boom, a spray of gas does)
Then start with tracing spark. Is the spark bright? Does it spark when the piston is at top dead center? Or did you jump timing? (how many miles) Keep backtracking the wiring to see if the computer is sending the wrong signals to the ignition / fuel injection?

Good luck
 
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I tried swapping in a spare TPS and it wouldn't start. I also tried the air flow sensor next to the TPS. Still nothing.

I'm pretty sure There isn't water in the fuel. The night before it quit running, I filled the tank all the way up and drove it at least 25 miles then parked it in the shop over night and it started up right away in the morning, drove it out of the shop for a minute then back in.

If it was an issue of timing of the injectors or spark wouldn't I atleast get some sputtering or backfiring when I turn it over? It has good spark, I cleaned a spot on the valve cover and laid a plug on it and it made a good bright spark. Treeclimber mention "jumping the timing" how would I do that? What does this do? Does the crank pulley have a timing mark so that I could put a timing gun on it to check that its firing at TDC? Is it possible to check injector timing?

If I haven't tried starting it in several hours, when I first crank it over, it fires and sounds like it is about to start right away, then it just keeps cranking. If I stop cranking then start again right away, it doesn't sound like it will start, it just turns over. Maybe its getting flooded? Is 40 PSI TOO much fuel pressure?
 
40 might be a bit too high. not sure what thats supposed to have.

i know on my 4runner, its VERY picky about fuel pressure. 1-2 lbs too low, and it will NOT start. like a switch, once it hit 35(or whatever was correct, i cant rememebr now) it would fire right up.
 
You have tried swapping in a new CRANK POSITION SENSOR, right?

Co-Man-Che said:
I tried swapping in a spare TPS and it wouldn't start. I also tried the air flow sensor next to the TPS. Still nothing.

I'm pretty sure There isn't water in the fuel. The night before it quit running, I filled the tank all the way up and drove it at least 25 miles then parked it in the shop over night and it started up right away in the morning, drove it out of the shop for a minute then back in.

If it was an issue of timing of the injectors or spark wouldn't I atleast get some sputtering or backfiring when I turn it over? It has good spark, I cleaned a spot on the valve cover and laid a plug on it and it made a good bright spark. Treeclimber mention "jumping the timing" how would I do that? What does this do? Does the crank pulley have a timing mark so that I could put a timing gun on it to check that its firing at TDC? Is it possible to check injector timing?

If I haven't tried starting it in several hours, when I first crank it over, it fires and sounds like it is about to start right away, then it just keeps cranking. If I stop cranking then start again right away, it doesn't sound like it will start, it just turns over. Maybe its getting flooded? Is 40 PSI TOO much fuel pressure?
Click to expand...

The crank shaft and the cam shaft are connected via the timing chain (or belt, in some cases) and, as the engine wears (or gets old) the teeth of the gears get worn down, and the chain stretches. Eventually, the chain 'skips' a tooth or two, and the chain has 'jumped timing'. What that means, is that the spark plug is no longer in sinc with the opening and closing of the valves. So, it may be firing on an open combustion chamber, instead of when the engine is on the compression stroke.

The easiest way to check, is to pull the number one cylinder, and slowly have a buddy crank (use the key) the motor over as you keep one finger in the spark plug hole. As the compression cycle goes, it'll force air past your finger. Meanwhile, you're watching the timing mark on the timing gear (crank pulley) to make sure you're coming up to top dead center. Then cross reference the distributor to see if the rotor (of the cap & rotor) is also pointing at the number one plug wire.
 
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I did try the CPS. When you said "jump the timing" I thought you meant overriding the computer control on the timing. I don't think its a timing issue though because it would atleast backfire or run really crappy.
 
Co-Man-Che said:
I did try the CPS. When you said "jump the timing" I thought you meant overriding the computer control on the timing. I don't think its a timing issue though because it would atleast backfire or run really crappy.
Click to expand...
not the the cam timing. if it was off..it might not run at all.
thats different than ignition timing.

how many miles does it have?
 
Finally! Turns out it was the fuel pressure regulator. Swapped in a used one and it fired right up. Thanks to everyone for their thoughts and suggestions!
 

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