Rough idle

[FastWoman]

Jan, I had your exact restart / rough idle issue. One way or another, the problem is air inside your fuel rail. When you try to start the car, you're injecting air. Once the fuel pump is able to purge the air through the return fuel line, approximately half of your injectors are still going to be injecting air, because the fuel rail is in a loop, and only one end of the loop will initially get purged (whichever one is lower). It will take longer to work through the air in the higher end of the fuel rail. So when you eventually start, you're running approximately on 3 cylinders, although conveniently you're missing every other explosion in the firing order. Then your other three cylinders will catch, one by one, as the air is purged. Probably your #1 or #6 will be the last to catch.

Solutions:

1) Get your fuel rail tight. You've replaced the injectors, aside from the CSI. My CSI was frozen partially open, and I replaced it with a used part I had on hand. I then got my original one cleaned out by flushing with Chemtool B12. It holds pressure now. Finally, there's the fuel pump check valve, which Cozye correctly indicated is NLA. Even the corresponding Volvo check valve seems to be NLA. I know, because I probably bought the last one in the country. Another solution that might work is an inline check valve, which you could place inline between your fuel filter and fuel rail:

http://cgi.ebay.com/ebaymotors/One-way-Check-valve-Gas-Diesel-fuel-5-16-Bio-_W0QQcmdZViewItemQQhashZitem230dbe3583QQitemZ150554424707QQptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

I had checked with the seller to determine that it would work fine for 30'ish psi pressures. He said it would be. I don't know anyone who's installed one, but you could be the first to try it!

2) If you can't get your system 100% tight, and/or if fuel vaporization becomes a particularly difficult problem down there in AZ, you can install a primer switch that will manually power the coil on your fuel pump relay. I did this on my '78, prior to working through the leaky fuel rail issues, and it worked magnificently. With the primer switch, you can just run the pump until the air is purged. About 10-15 sec of purge will even clear the bubble in the higher end of the fuel rail, assuming you're on a reasonably flat surface, so that your engine isn't coughing and struggling when you turn the key.

Edited January 28, 2011 by FastWoman

[anthony280z2+2]

This also happends to my z. Exactly the same. The only difference is that I have problems starting it.the starting problem recently happend but before that this was the only issue,and still is when I drive it.comparing post is giving me an idea of my issue.

[Z train]

His plugs read textbook perfect.And the problem came & went while we were standing there.

[FastWoman]

Then it's not just on startup??? I'm confused. I thought from post #8 that I understood what he was referring to.

I would think that any issue that both comes and goes while you're just standing there looking at the car idle almost HAS to be an intermittent electrical problem. Are all the electrical connections clean? Are the connectors in good shape?

[anthony280z2+2]

The start up problem is new but the other one has been for a while now. It starred with the same problem as pomorza. Then the car would only start if it was warm outside, then eventually to now how I discribed at my "stomp" post.

[Z train]

Then it's not just on startup??? I'm confused. I thought from post #8 that I understood what he was referring to.

I would think that any issue that both comes and goes while you're just standing there looking at the car idle almost HAS to be an intermittent electrical problem. Are all the electrical connections clean? Are the connectors in good shape?

He started the car and it had the issue.While we were standing he whacked the throttle a few times and it vanished.

[Pomorza]

He started the car and it had the issue.While we were standing he whacked the throttle a few times and it vanished.

Exactly what Z train said. We start the car after I drove to Ztrains place after letting it sit for, oh ten minutes maybe. Problem was clearly there. While sitting trying to figure out problem we revved the engine a few times (4 or 5 maybe) and the said problem went away.

To be honest it sound that FastWoman is right on this one though. Z train, although the issue was there and the plugs were dead on, as you told me since the car "fixed" itself it is possible the plugs would show any sort of lean/air mixture.

I'm going to go ahead and replace the fuel related devices as I have nearly everything but the actual pump. (I have the dampener, regulator and the CSV)

Jan

[cozye]

what you are explaining could still be the normal hot start issue. The fuel rail loses pressure slightly, gas boils a bit putting air in the fuel rail, you restart the car 10 minutes later, and after reving it a few times it goes away..

The reason why is like Sarah stated. The fuel rail has air in it. When you rev it up, the FPR opens a little since it gets high vacuum on it, which circulates fuel through the fuel rail faster. If yours did like mine, you can put your ear up to the passenger side floor board while you are revving it up, and actually hear the bubbles in the fuel rail being sucked though.

Whatever the fix is, the cause is a leak down in your fuel pressure somewhere.

Also, if you suspect the check valve, you can pull it off the fuel pump (it's the outlet nipple). It comes off with an open end wrench. What I did to test it was I pulled it off, inspected it, sprayed some lube in the spring etc.. and put some air pressure on it against the flow to see if it would hold air pressure.

I wouldn't bother replacing the dampener yet, as it's not a source for pressure leak down and I don't think it's too common for those to go bad and cause issue.

Also don't forget that a leaking injector could quite possibly be the culprit.

[Pomorza]

what you are explaining could still be the normal hot start issue. The fuel rail loses pressure slightly, gas boils a bit putting air in the fuel rail, you restart the car 10 minutes later, and after reving it a few times it goes away..

The reason why is like Sarah stated. The fuel rail has air in it. When you rev it up, the FPR opens a little since it gets high vacuum on it, which circulates fuel through the fuel rail faster. If yours did like mine, you can put your ear up to the passenger side floor board while you are revving it up, and actually hear the bubbles in the fuel rail being sucked though.

Whatever the fix is, the cause is a leak down in your fuel pressure somewhere.

Also, if you suspect the check valve, you can pull it off the fuel pump (it's the outlet nipple). It comes off with an open end wrench. What I did to test it was I pulled it off, inspected it, sprayed some lube in the spring etc.. and put some air pressure on it against the flow to see if it would hold air pressure.

I wouldn't bother replacing the dampener yet, as it's not a source for pressure leak down and I don't think it's too common for those to go bad and cause issue.

Also don't forget that a leaking injector could quite possibly be the culprit.

Since I got all the parts already,dampener included, I might as well replace it wouldn't you think?

I'm tempted to say that my fuel pump is nearly 20 tears old, as all the paper work indicates that it was replaced sometime between 90-96 so I am willing to bet that the pump isn't in the best shape anymore.

Jan

[Z train]

what you are explaining could still be the normal hot start issue. The fuel rail loses pressure slightly, gas boils a bit putting air in the fuel rail, you restart the car 10 minutes later, and after reving it a few times it goes away.

Not warm enough here for the hot start issue.And there was no loss of FP.

[cozye]

Not warm enough here for the hot start issue.And there was no loss of FP.

Mine has done it as low as 45 degrees, and the fuel pressure doesn't drop for hours. What would happen would be just enough leak for the air to come in the line, then the boil would actually raise fuel pressure up on the fuel gauge to about 37 or so within 5 minutes. All it takes is a slight leak to drop the fuel pressure low enough and introduce a little air for it to start a boil. Once it boils just a little, the pressure actually rises. I was told that's how to tell if I had the hot start/vapor lock issue. If you don't have it the fuel pressure shouldn't move at all once the car is shut off. If I left it alone overnight the fuel pressure would eventually leak down. I believe gas will boil at 29 psi or so. Feel the fuel rail when it's shut off, even in this cooler weather its too hot to the touch.

Mines not doing it now since I replaced the leaking cold start valve. Seems to be holding fuel pressure for days.

In any case, he's got a leak in the fuel pressure somewhere.

Edited January 30, 2011 by cozye

[cozye]

Since I got all the parts already,dampener included, I might as well replace it wouldn't you think?

I'm tempted to say that my fuel pump is nearly 20 tears old, as all the paper work indicates that it was replaced sometime between 90-96 so I am willing to bet that the pump isn't in the best shape anymore.

Jan

I'd worry about messing with the fuel lines to replace the dampener, unless you are replacing lines and clamp. I'm sure there is nothing wrong with it.

My fuel pump is the original, its 33 years old If it puts out a steady fuel pressure I'm sure its fine too. I've got a spare though.