'94 5.7L rough idling problems, possible fuel pump. Need ideas/suggestions.

[LSUfan71]

Fuel filter improved idle only slightly.

 

[LSUfan71]

Wow, it must be impossible to move the fuel inlet away from the TBI to get a fuel pressure gauge on! Trying.

Can I connect the gauge at the fuel filter exit?

 

[LSUfan71]

Your engine code is just 12. Which is just checking to make sure the bulb is good. With no other codes your computer isn't reading any problems with the truck.

The timing on the tbi motors is very touchy if its off even by a few degrees it will run like crap, if the mechanic replaced the distributor and didnt time it right that could be your problem

I'm getting a steady 12 psi repeatedly with the fuel pressure gauge connected to the exit side of the fuel filter. Fuel pump stays on for 2 seconds and goes off, looks like I'm doing it correctly.

 

[beaugott]

Could be the EGR valve. I just replaced the one on my 95 suburban because my truck had a horrible idle and would stall under load. Took care of both problems. Try unplugging it to see if the truck will idle and if that fixes the idle replace it.

 

[LSUfan71]

Could be the EGR valve. I just replaced the one on my 95 suburban because my truck had a horrible idle and would stall under load. Took care of both problems. Try unplugging it to see if the truck will idle and if that fixes the idle replace it.

I'll test it. Right now it misses while idling. It will idle steady for 5-10 seconds then drop RPMs and die. I can keep it running by tapping the accelerator when the RPMs drop.

 

[95chev]

This truck doesn't have an after market cam in it does it?

 

[axisT6]

I can't believe noone mentioned vacuum leaks. A vacuum leak on can cause a very rough idle. I speak from experience here. Before replacing any sensors, check the hoses on top of the engine for any knicks, cuts, cracks, or holes. In fact, if you still have the original hoses on top of the motor, replace them all with fuel line.

If your mechanic "visually checked" checked the timing chain, that means he removed the fan, water pump, and timing chain cover.... If you pull the black and tan wire, your timing should read 0*.

 

[LSUfan71]

This truck doesn't have an after market cam in it does it?

I don't think so. The previous owner said it never had any mechanical probs, but now I know he was lying (of course).

I can't believe noone mentioned vacuum leaks. A vacuum leak on can cause a very rough idle. I speak from experience here. Before replacing any sensors, check the hoses on top of the engine for any knicks, cuts, cracks, or holes. In fact, if you still have the original hoses on top of the motor, replace them all with fuel line.

If your mechanic "visually checked" checked the timing chain, that means he removed the fan, water pump, and timing chain cover.... If you pull the black and tan wire, your timing should read 0*.

Precisely. One of the last things my mechanic told me after he couldn't fix my truck for 3 weeks was that he was "certain" the timing was fine. So after all this time I decide I'll check the timing myself, I began to suspect that he didn't disconnect the tan/black wire (disconnect the EST). I bought a shiny new timing light, marked 0º on the timing plate and the notch on the damper with Liquid Paper, I disconnected the EST and what to my wondering eyes did appear? Nothing. He obviously installed my new distributor 180º off. That was late last night, it was cold so I quit in disgust. And the engine was idling better...

Going back at it this morning in the chill, gonna put #1 back at TDC and check the distributor. I'll report back here later this morning.

I've replaced all the vacuum lines, doesn't seem to be a vacuum leak.

 

[LSUfan71]

I installed a new MAP sensor also, that seemed to help some.

 

[LSUfan71]

With the #1 cylinder at TDC the distributor drops in at only two different spots, 180º from each other. These are relatively located on either side (90º from pointing to the front or rear). I put the distributor in with the rotor pointing to the driver's side, which is where I assumed the #1 spark plug wire would be. After putting the cap on and making sure all the spark plug wires are properly connect I'm getting no start (cranking tho).

I thought it should be fairly straight-forward to install a distributor with #1 cylinder at TDC. Thoughts?