A couple days ago I took off my fuel rail to get the schrader valve out. Ever since then, the car runs rough, runs very rich, and when I crack the throttle quickly, it nearly dies. Sometimes it does die, and when that happens it will barely start, and runs very roughly for several seconds. On normal driving it runs fine, the problem seems to happen when a) I first start it and b) when I quickly blip the throttle open.

Thinking I might have ruined the fpr, I tested it and it's 40 at idle and jumps to about 52 when you pop the throttle. Tonight, I put in a new set of injector o-rings and a new set of plugs. Two of the plugs had some brownish fouling.

What could I have done in the process of removing the fuel rail that could cause this?

 

Pull the rails again and leave everything hooked up, now get a container and hold the rail assembly over it and turn the key on, so the fuel pump primes. This will allow you to see if you have a leaking injector.
Sounds like your getting too much fuel and the only way removing the rails could cause it is if one of the injectors got damaged.
Have you done a leak down test on the fuel pressure? Is it holding steady for awhile after the car is shut off?
FPR could be bad but you should smell raw fuel in the vacuum line if the diaphram is bad.

 

Could be a vacuum leak, too. Pull the rail and make sure the lower injector o-rings are on and not damaged. When you put back the rail, coat the lower inj rings with oil, so they can slip into thier holes easily and make a better seal.

 

I bet its one or more of the lower o-rings. Some time ago I installed my fuel rail back and it worked fine for a while but then all of a sudden it began to run rich on one bank. Pulled some of the plugs out and they were fouled up. She too would try to die when I gunned her up. (I talk funny dont I?) See... she was running so rich.. when I gunned her.. she would foul up the plugs inmediately.


By chance... I leaned over the side and my eyes landed on the # 1 injector...... I notice a piece of the o-ring sticking out. When I intalled the fuel rail back on the o-ring had caught the edge of the cylinder head and gotten stretched out and stay put till it got ripped apart by the heat cycles later on I guess.


The first time around I had coated the O-rings with oil...This time I used Grease and The fuel rail slid back on so much easier this time and The problem got fixed. No more Vacum Leaks and No more plugs fouled up.


Our LT1's are so sensitive to vacum leaks that the most insignificant misfire or additional air in the intake becomes a Big Drama that I swear its like dealing with an ovulating fe...m...err never mind.. . But you know what I mean.

I bet you have a vacum leak from a torn or missing O-ring

Marvin

 

Did you put the vacuum line back on the FPR and the intake?

 

Guys, I appreciate the help.

Revtime: It does hold fuel pressure steadily for quite a while after key-off. I can't tell you exactly how long, but I watched it for a minute or so and it stayed right at 40. I'll do the test you mentioned in the very near future.

Hungry: I replaced the O-rings yesterday, and I did lube them before installing them. I don't think the old ones were leaking because 1) I can see a ring of clean rubber all the way around and 2) replacing them didn't help. At this point I'm 100% sure the o-rings are not the problem.

Mental: the plugs I took out were not fouled, but the bottom of the metal body had some soot on them. To me, this seems to indicate that it's running rich periodically, but the plugs are definately still firing. This is also backed by the fact that it doesn't run any better with new plugs.

One other thing: I bought the Trigger from harris speed works (electronic WOT switch) and it's wired incorrectly. They suggested tapping a certain color wire, but I tied into it and the switch doesn't work as designed (though it does work on test so all but 1 wire are correct). I'm going to check to be sure that we didn't tear the splice on that wire.

My new plan of attack: Buy a vacuum tester (test egr valve and check for vacuum leaks), check the wire on my TPS, check for stuck injector.

 

Did you miss my post?

 

Lodre: I did put the vacuum back on the FPR, and it's hooked up at the other end (meaning it does have vacuum). I did a visual and I cannot find any obvious vacuum lines disconnected.

If I understand correctly, when you blip the throttle, the car reads tps voltage and possibly maf voltage. Is that all? Surely a bad egr valve would not enter the equation, would it (I know mine is not working right). Seems to me that the pcm sees a rise in voltage at the tps, which tells it to add fuel. Does it do that based on a predetermined table like DFI6 or does it take into account O2, MAF, and TPS values (assuming <WOT because it runs almost right at WOT)? I'm trying to understand what systems are affected so I know what to test and inspect. A buddy has a Snap-on diagnostic scanner that will trouble shoot these things with amazing accuracy, but he's busy for the next couple days and if I don't get this thing running right, I'm going to have to drive a 1 ton dually 400 miles this weekend. With gas at today's prices, I'm not excited about that.

 

What about your EGR vacuum line. It pretty much has to be a vacuum related issue. Go get a can of carb cleaner, etc, and spray all around everything vacuum related on the intake (hoses, lines, tops and bottoms of injectors) If your idle rises (do this with the car on BTW) when you spray a certain area then you have found your leak.

 

Why did you remove the fuel rails to take out the valve?

If you have a problem with a poor sealing injector o ring, you will run into a lean condition, not rich.

 

As you were typing that I was outside doing just that. I found one lower o-ring that I can see from the top, so I need to replace that one again. I was just so sure I wouldn't have screwed that up...

As far as I can see, there isn't any new vacuum leak.

I checked the tps wires and cut the trigger wire off, and bypassed my 685 box, to no avail. Then I went to drive home and the car only made it a block, then it started cutting out badly, jerking. I thought it was out of fuel, so I headed back and when I got it to the shop the ses light was flashing- misfire! I have a good idea that this is the cause- loose plug wires. Right after I got the car it did almost exactly the same thing, and my buddy's scanner said that two wires were bad. Sure enough, they were. Now I have the accel wires that are almost burn-proof so they are probably just loose.

It was getting late so I drove the truck home, but I'm going to check the wires tomorrow.

 

I took the valve out, but it seemed like part of it was missing because what I had in my hand didn't seem to have a seal on it. I took off the rail to check and the lower part of the schrader valve- the seal- was still in there.

 

Not sure of your mods, but that pressure seems awfully high. Do you have a stock FPR? Stock injectors?
I don't believe any of the vaccum lines running off the manifold will affect idle significantly except for the brake booster.

 

Injectors and fpr are stock.

You guys were all right; my injector o-rings were bad. When I installed them, I put one of the old ones back in (in the dark) and cut a chunk out of another. It did have a loud vacuum leak that I fixed by putting in another set of o-rings. I hate to say it, but I'm confident there are no further problems with the o-rings. I will definately get a vacuum tester this weekend and see if a leak shows up, but there aren't any obvious leaks.

It still runs exactly the same. Rich as all hell, and it dies sometimes when I let off the gas.

My buddy, who is a sharp mechanic, says it might be the MAF. He told me to unplug the maf when the car was stone cold and see how it runs. In that situation I couldn't make it stumble. That lead him to guess that the MAF could be bad. I'm going to swap out my buddy's maf this weekend and see what happens.

 

Man I still think you have a vacum leak there somewhere... also your fuel presure is way to high...

You sure you put grease on the new ones before installing them? Here is a tip... if the fuel rail does not slide down smoothly and with little effort... something is not fitting right.


Marvin