A few weeks ago the fuel pump went out. Through some miracle i was able to nurse the car all teh way across town (probably 10-15 miles) to my house. Replaced the fuel pump, car ran real rough. Due to driving with such lean conditions I went ahead and changed all the spark plugs and while I was at it, changed the wires to. Dialed in the base timing to 6* BTDC. Engine still runs rough, especially when cold. Once the car warms up, it smooths out, but still idles rough. Any ideas why it is so rough? Could there be engine damage due to the lean conditions? Trying to sort this out. Thanx in advance.

 

I don't think you did any damage, even if it were possible, the engine wouldn't run better warmed up.

It was fine before the pump went out?

SES light on by chance?

Possible on cold starts, the Cold Start valve may not be working

 

no SES light, that would be easy.

car ran fine prior to the fuel pump failing


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Disregard the CS Valve...initially I was think rough to start...

You did disconnect the EST bypass when setting the base timing?

If you're sure the wires/plugs are fine after replacement, and since the only other thing changed was the pump, you may want to check the fuel pressure on a cold start...would be odd it's not consistent, but never know. At least you could rule out/confirm a faulty pump.

 

I did disconnect the EST connector when setting base timing. Does it matter if it is set hot vs cold?

I am leaning towards something in the system not allowing it to hold static fuel pressure. I rebuilt the FPR, no fix. Maybe I need to install a primer switch that activates the fuel for as long as i hold it.

 

I don't think it's needed.
How long before it smooths out?

I/e a few seconds...or when it goes into closed loop? (about 150 F) then runs okay?

 

when it gets to closed loop it runs fine


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For S's and G's, next cold start unplug your MAF.

 

what would that do?

 

It'll (ECM) use a preset value for the parameters, in lieu of using the MAF, it'll set a code, but just clear them afterwards

 

Fuel filter.

Running better as it warms up is a dead giveaway to a lean issue.

 

fuel filter was changed 2 weeks ago.

Tried the whole MAF unplugged thing..no fix.

 

What pressure at the rail?

 

My fuel pressure gauge is broken right now (yay Garbage Freight). But, when I did the fuel pump the gauge did work, and it read about 45 psi at the rail.

Pulled the #1 spark plug to see what it looks like. Bear in mind, this plug has only been running for a week. Note how only one side is burnt. Is that good?

 

Got my fuel pressure gauge fixed. pump puts out about 45 psi. Pinched return line, turned off pump, held pressure. Let go of return line, went straight to 0. Put in new guts in the FPR, no fix. Looks like I need a whole assembly. is there any way to swap out the FPR itself, or do I have to do fuel rails also?

 

check the o-2 sensor, sometimes when run lean, they get fried. but first run the codes

 

checked codes, none. I believe the FPR is cracked internally, needs replacing.

 

Fired up the car today. 0 psi on the fuel pressure gauge, hit the key, fired right up. Gonna let it sit for an hour or so and see what happens.