Stuck in DQ drive thru

[Bobmbx]

Had a memory code for IAT above max voltage, we did have it unplugged saturday night while the engine was running, live data voltage of 2.9

TPS voltage looked normal, it is brand new
O2 .03-.80, the .03 seems a little low after reading Glacier's fantastic thread
timing advance ranged between 21 and 24 degrees
injector pulse 2.2

I am in no way remotely good at diagnosing engine problems, especially on these odler models. Big thanks to all who are helping me.

How old are your spark plug wires?

 

[Four0Sport]

2 yrs but less than 5K miles

bought my own fuel pressure gauge, started to thread the adapter onto the valve, and it started taking the threads off of the valve. dangit.

 

[Four0Sport]

just to rule something else out I tried a new MAF, no change. added fuel to the truck, reset pcm, let run for 45 mins and still have the idle/surging problem.

as Anime stated, I will be removing the pcm tomorrow to check it out. any way to test the ICM? been reading some threads but haven't seen anything yet.

 

[arco777]

On a 94 X I used to have, I had somewhat random stalls. Seemed almost like the PCM was bad. I'd be coasting to a stop or at a stoplight and it'd just shut off. I had to turn the ignition off, wait up to 30 seconds, and try to start again and it'd run. Diagnosis was tough as I couldn't ever replicate the problem in my driveway. Strong fuel pressure, strong spark. I tried swapping PCMs with no effect.

Eventually when my wife was driving alone the truck stalled and refused to start again at all. Testing fuel pressure showed zero this time. It turned out that my 2 month old Bosch "improved turbine design" fuel pump was randomly stalling due to a defect.

 

[Four0Sport]

Updates. Checked ecu, ignition module, and fuel pressure again. Here's where it gets interesting. Hooked up gauge and turned key on. Had to cycle 3 times to get pressure to 30psi. When cranking it went to 40, started then back to 30. Removed vac to fpr went to 40 psi. Idled at 30 for 3 mins then I shut it off and removed the gauge. Went to start it and it would only crank, no fire. Did this 3 times. Hooked gauge back up and pressure low, started on third cranking attempt. After all of these readings when shutting off the pressure immediately fell back to zero. Removed gauge, started, let run 45 mins rough idle still present.

Here's where it gets interesting-er. I'm one of 12 finalists for this year's ultimate adventure. So hopefully you can all understand why I'm panicking. I need some help.

 

[2000StreetRod]

fuel present in vacuum hose?

When you disconnected the vacuum hose to the fuel pressure regulator (FPR) was any fuel present? If so, then the FPR diaphragm is cracked. However, the FPR seems to be functioning normally with and without vacuum.

I don't know about the 1st Gen but on the 2nd Gen there's a check valve in the fuel pump assembly that prevents the fuel pressure from immediately dropping to zero when the pump stops running.

 

[Four0Sport]

No fuel present in any of the vac lines, replaced FPR already.

I. Am. Stumped.

 

[2000StreetRod]

sticking check valve?

If the check valve in the fuel pump assembly is sticking open then that would explain the immediate drop in fuel pressure when the pump shuts off. But if the fuel pump is good and maintains the correct fuel pressure at the fuel rails that would only affect engine start and not engine running. A sticking check valve would not explain the excess fuel pressure (65 psi) you experienced earlier. If the check valve had stuck closed earlier the fuel pump could reach its max pressure but that would not exist at the fuel rails. Did you replace the FPR before or after the 65 psi reading?

 

[Four0Sport]

After

 

[2000StreetRod]

crankshaft position sensor?

. . . Went to start it and it would only crank, no fire. Did this 3 times. Hooked gauge back up and pressure low, started on third cranking attempt. . .

If your fuel pump is functional then there should be 30 psi or so on the fuel rail anytime the starter is cranking. The crankshaft position (CKP) sensor "notifies" the PCM if the crankshaft is rotating. If the PCM doesn't get the notification when the engine is cranking or running then the PCM disables the fuel pump for safety reasons. A faulty CKP sensor can cause intermittent starts and an unsteady idle. You might try cleaning the CKP sensor connector by disconnecting/reconnecting it a couple times.

 

[Four0Sport]

cleaned all mud and gunk and grime away from and off of the CKP sensor, cleaned the connector and the terminals on the sensor. Truck starts faster.. but still the same idle problem once it is in closed loop. I think I am using the right terminology. Honestly.. I am about to sell an organ and find someone to throw the 302 in it for me.

 

[Four0Sport]

oh, we can eliminate the catalytic converter too. don't ask me how, i regret it.

 

[Four0Sport]

removed the IAT sensor and it was wet and smelled like fuel. but the vac lines do not. hmm. changed it since there had been a code for high voltage stored in the system. no change.

 

[Four0Sport]

update.. after unplugging and plugging in connectors, replacing sensors and removing the converters the truck hasn't had any issues. Until this morning. went to get a new inspection sticker and the truck would not start. crank crank crank no fire. opened the door and turned the key and did not hear the fuel pump kick on. checked fuse and relay and inertia switch, still nothing. hmm. so i came in here and started reading some diag threads for bad fuel pump. walked back outside and it started right up. this is the the first time it has done this as it happened during the fuel pressure tests and randomly over the past year or so it has happened a couple times.

soooooooo fuse and relay good, inertia switch good, random no power to the pump. I know I need to start checking wires but now that it has started I'm kind of at a loss at where to check first.

ideas/suggestions welcomes, as always..

Now I am even farther behind for Ultimate Adventure. geesh.

 

[2000StreetRod]

intermittent fuel pump

I suspect that the brushes on your fuel pump are worn down making unreliable contact. An old pump is more likely than bad wiring connections. If cycling the key a few times or banging on the fuel tank with a rubber hammer makes a difference (pump runs when it first didn't) then the problem is either the pump, the fuel pump relay or the ignition switch. If you still are using the original pump it is probably due for replacement.

 

[arco777]

I submit post #24 again. Sounds very similar to what I experienced with my defective Bosch pump, down to the pump randomly not starting.

 

[Dano!]

Try checking the electrical connections on your sending unit. If you pull the sending unit check the connections on the inside too. The plastic bushings can wear out and give you intermittent fuel issues until they fail completely. I have a old thread on my experience with something similar. Phones about to die but it's titled something like Dano navajo is back on the road.

Hope it helps

-Dano

 

[Four0Sport]

thanks for the tips guys!