I dropped the tank the Friday and cleaned it out and installed a new fuel pump and put a new fuel filter on while the car was on stands. I then filled the tank and poured a can of seafoam into it to clean out the injectors and such. Car ran like a champ on the test drive. Today though is a different story. I drove it about twenty minutes across town and by the time I was getting to my destination it was starting to stumble and was having a hard time under load. The car sat for about two hours before I started driving home. It ran fine for the first block or so and then started the stumbling again. It got a lot worse quickly after that getting to the point where it would barely get up to 20 mph. If I stepped on the gas at all it just bogged down and barely ran and if it idled more than a minute or two it would die. I pulled it off to the side and let it sit a few minutes and it started right up and ran a little better for about a block before doing the same thing again. I checked the schrader valve on the fuel rail and it squirted gas when depressed so it seems to be getting fuel at the top of the engine, but it acts like its running out of gas. It fires right up everytime, but it will die after about a minute or so of idling. I was able too barely make it home, but by the time I did it was crawling along and back firing pretty bad. Any ideas gents?

EDIT - Tach started jumping around like crazy a couple weeks ago, it ran fine though. Don't know if it related at all.

[This message has been edited by mr_corean (edited 03-02-2014).]

It sounds like the Seafoam has freed up gunk that has clogged the fuel filter.

Check the fuel pressure if you can. If you don't have a gauge then what I've read is that it should squirt high enough to hit the decklid.
If pressure is lacking, changing the fuel filter might help.
If pressure is good, maybe it just needs more good fuel added. I don't know if the Seafoam could have caused this problem, if so diluting it some more might help.

quote Originally posted by Ang84Indy: It sounds like the Seafoam has freed up gunk that has clogged the fuel filter.

I thought about this, but since I cleaned out the tank, put in a new pump and filter, and new hoses from the tank to the filter, I didn't think there would be any gunk to get into the filter. I'm not ruling this out though.

It could also be a bad fuel pump. What brand did you use? Some cheaper ones are known to be bad right out of the box.

Aeromotive. Can't get a fuel pressure tester right now, but the fuel is hitting the deck lid when the schrader valve is depressed with a screwdriver.

Sounds like the Seafoam may have dislodged something. Could be debris in the sock, the filter or the injectors themselves. If you have access to a fuel pressure gauge , you can check the rail an narrow it down quickly. Since you have injector cleaner in the tank, there is a good chance this will improve with running, which sounds like what you're seeing.

i recently run into this myself but not on a fiero. when slowly rolling into the throttle it would rev up to redline but when you dump into it hard it would fall on its face. What i found was a piece of trash under the diaphragm of the pressure regulator. when slow pedal applied the diaphragm didnt move as much but when a hard load was applied the diaphragm would move fast and the trash would block it. causing poping and backfiring (going lean) Hope this helps.

In my years of experience the most overlooked piece of a car is the diaphragm of the regulator, in 6 years you might change your fuel filter 4 or 5 times and fuel pump twice and strainer twice too but hardly anyone ever changes the Press reg diaphragm and alot of hunting idle problems is caused by the Press regulator.

[This message has been edited by dematrix86gt (edited 03-02-2014).]

quote Originally posted by dematrix86gt: What i found was a piece of trash under the diaphragm of the pressure regulator....

Interesting.

I'm not really clear on this. Was this piece of "trash" within the fuel system?

what it was was scaling on the inside of the fuel line from bad fuels. as with this guy he used a additive knocking the scaling loose and it went straight to the regulator. i opened the reg pulled the Diaph. and found it. put a glass jar up for a capture sample , kicked the key on and flushed the line. captured more doing this. so i used a line brush and run it from TB to fuel filter and was suprised to see how much varnish and scaling actually come out. The car run perfect afterwards. Additives work good but sometimes too good.

quote Originally posted by dematrix86gt: ...i used a line brush and run it from TB to fuel filter and was suprised to see how much varnish and scaling actually come out.

How much fuel line we talking about here? A few inches? A few feet (as when the filter is under the car)?

almost 3 and 1/2 feet. filter was under drivers door on inside of the framerail. i can scrub up to 10 feet with my line brush., i actually made the brush out of a old gun bore brush and speedometer cable.

[This message has been edited by dematrix86gt (edited 03-02-2014).]

quote Originally posted by dematrix86gt: almost 3 and 1/2 feet. filter was under drivers door on inside of the framerail. i can scrub up to 10 feet with my line brush., i actually made the brush out of a old gun bore brush and speedometer cable.

With a situation like that, you sort of wonder why the fuel filter isn't always located as close to the TB (or fuel rail) as possible (OEM or otherwise).

If there's an issue at the regulator, it should show up when testing with a pressure gauge. Just make sure to keep the gauge connected with engine running and see what happens to pressure when the problem is recreated.
The fuel pressure regulator is referenced against manifold pressure - is there any chance you have a vacuum leak in that connection? With the throttle more open, manifold air pressure will increase. If the pressure regulator doesn't compensate for this then the injectors will have a harder time spraying fuel and it would go lean.
If you get a gauge on it then watch to see if the fuel pressure tracks with manifold vacuum. It should.

This could also relate to possible sensor issues at the TPS and the MAP, but since the fuel system has recently been a concern that's probably the primary suspect.
The vacuum to the fuel pressure regulator and the MAP sensor are connected at a "T", which share a common connection at the passenger side of the upper plenum.
If you poke around in that area, one other consideration is that sometimes a bad regulator will leak fuel into that vacuum line. I don't think that in itself would cause your symptoms but if you find fuel in there, it's a sign of failure.

quote Originally posted by Patrick: With a situation like that, you sort of wonder why the fuel filter isn't always located as close to the TB (or fuel rail) as possible (OEM or otherwise).

Agreed.
I suppose manufacturers might worry about the possibility of fuel leaks that close to a hot engine and exhaust. Putting the connections for a filter up there increases the chance of that happening. But it would certainly help the filter to be more useful than it seems to be.
It is fairly close on the 4cyl Fieros at least, while still keeping it in a pretty safe location. On the V6s it's like halfway upstream.

Is your car throwing any codes? Could be quite a few posibilities...Yea, I agree might be the fuel pressure regulator as "dematrix86gt" says.

Has anyone tried using the winaldl program to diagnose a problem like this so the fuel pressure and spark and etc. could all be seen while the engine is running?

I got hold of a fuel pressure tester from a buddy today at work. Unfortunately it didn't have the correct adapter to work with the car. It will screw onto the schrader valve but not engage the pin in the middle so I am back to making a trip to harbor freight for one. In the mean time I took apart the upper fuel system and cleaned it all up. I opened up the fuel pressure regulator and it was clean all the way through. All the injectors clicked when tested, but I don't have a way to flow test them. I put it all back together and tried it again figuring that nothing would have changed and guess what!? Nothing changed. I did notice when purging the fuel line at the valve though that a lot of air comes out of it first whenever the car is starting to get into its barely running state. When I turn the car off and let it sit long enough for the pump to prime when the key goes back on the car runs fine. Not sure where it is getting all the air from since I went through and rechecked all my lines and they are good. My next wild guess, while I'm waiting on this weekend so I can really get into the car again, was to hot wire the pump to make sure it was running full time and not pulsing or something and possibly sucking up some air. Car idles just fine for a lot longer, like 20 minutes or so before it starts eventually getting back into the barely running mode. New issue now though. To hotwire the pump I ran a switched wire from the cigarette lighter to the ALDL connector fuel pump testing pin. Now, if that switch isn't turned on the pump doesn't run at all. Checked my fuses and they are fine, but pump won't run with out the switch turned on. Won't prime or anything. I'm really starting to hate this car. More good news too. While checking the fuses under the dash I saw all kinds of wires down there spliced together. If I didn't have the title and the car registered I would have said the car was stolen at some point. Or else someone tried to install a keyless entry system. I'll track all that down once I get it back to running again. I guess that's why they say if it ain't broke, don't fix it. At this point I'm leaning towards dropping the tank again this weekend and taking it to a radiator shop to be cleaned out real good. Put a new filter in and go from there.

007 - The car is throwing a code 23. Had forever and never caused any issues before.

Csjag - I have never heard of that program before so I haven't used it. Sounds interesting though so I will look into it. Not sure how it can read fuel pressure though without a sensor on the regulator or after it. Might be interesting though.

I think the most frustrating problem you can run into on a car is one where a previous owner has monkeyed up the wiring to install some security system or remote start or keyless entry or whatever. Problems are inevitable, and the mystery wiring drives me crazy.

If that's what you think you're dealing with, I'd try to delete any such mods and bring the wiring back to stock if you can.

I don't think the wiring is the issue now. It ran for months reliably before this. I knew the tank was dirty as hell and the fuel pump was starting to act up, I imagine because it was sucking up all that crap. I changed the pump and did the sea foam and now this. Hopefully everything will get cleared up with a spotless tank this weekend.

Last night I finally made the trip and got a fuel pressure tester. It is on the car now and showing 38lbs while idling. It showed 45 with pump running and car off before I started the car up. When I rev the car up it will jump back up to about 43 for a split second then drop to 35. When I left off the gas it drops to 33 for a split second before climbing back up to 38 at idle. Just waiting for the car to get to the point where it stumbles and dies again to get the reading at that point. Fuel pump is still hot wired at the aldl connector since the pump will no longer run at all with out that setup. Will post update of fuel pressure readings when car dies.

Update - Car ran for about 30 minutes before it started stumbling. Fuel pressure was at 19lbs at idle and would drop to 12 when trying to rev. Obviously the car would stumble and pop the whole way in the revving process. I'm now going to assume that the issue is indeed before the fuel rail and drop the tank, get it cleaned and double check the pump. Fun, fun.

[This message has been edited by mr_corean (edited 03-07-2014).]

quote Originally posted by mr_corean: Last night I finally made the trip and got a fuel pressure tester. It is on the car now and showing 38lbs while idling. It showed 45 with pump running and car off before I started the car up. When I rev the car up it will jump back up to about 43 for a split second then drop to 35. When I left off the gas it drops to 33 for a split second before climbing back up to 38 at idle. Just waiting for the car to get to the point where it stumbles and dies again to get the reading at that point. Fuel pump is still hot wired at the aldl connector since the pump will no longer run at all with out that setup. Will post update of fuel pressure readings when car dies. Update - Car ran for about 30 minutes before it started stumbling. Fuel pressure was at 19lbs at idle and would drop to 12 when trying to rev. Obviously the car would stumble and pop the whole way in the revving process. I'm now going to assume that the issue is indeed before the fuel rail and drop the tank, get it cleaned and double check the pump. Fun, fun.

I could have missed it in posts above but your problem might be with fine particle contamination of the fuel injectors each of which has its own screen filter that will catch and hold debris. If that is the case you will see normal pressure at the rail however the fuel injectors due to blockage will not be able to flow enough fuel. A low fuel pressure reading briefly when coming off throttle after a rev is normal because a lot more vacuum is pulled on the regulator diaphragm than the idle vacuum briefly.

Got the tank back yesterday, one day turn around and only $100 so I'm stoked. Installed it last night and it runs like a charm again! I guess the sea foam broke up the garbage in the tank enough that the pump would start to suck it up after a bit until it clogged the sock. Super happy to have the car back on the road. Gonna start a new thread for the electrical issue on the pump now. Thanks for all the input and suggestions!.