Fuel Problems...I think

[silver_pilate]

I've been having an intermittant dying problem with my 91 GT, and I just pulled the codes on my car. Here's what I came up with:

Hard codes: -85 : canister purge solenoid circuit failure (had that
one for a while)

Stored codes: -87 : fuel pump primary circuit fault
-96 : fuel pump secondary circuit fault / high speed
fuel pump relay open

Anyone have an idea what this translates to? A buddy had the same codes come up and said that his EFI book talked about the code 96 referring to a secondary relay which increases voltage to the pump under loads. Mustangs only have one relay (under the seat) and don't use a secondary relay.

Could the relay cutting out when it gets hot cause both of the stored codes?


Here's the history:

It's happened 4 times both before and after I changed fuel pumps (from stock to a 190lph). It happens after extended drives, usually at least 60 minutes or so. Amount of fuel in the tank doesn't make a difference that I can tell.

I will drive the car for a while on the highway (as I said, usually about an hour) and then the car will stumble very briefly and/or just cut off (has always happend after I slow down and come to idle speeds or get in traffic). Usually, you can then start it and make it run for a block or two, the engine stumbling the whole while. Then it dies for good. It will usually start, but won't stay running more than 5-10 seconds. After letting the car cool off for 45 minutes to a couple of hours, it will start right up and run just fine.

So, here's what I was thinking:

-Possibly the TFI module is crapping out on me. It's the original unit with 140,000 or so miles on it.

-Also, could possibly be the fuel pump relay getting hot and flickering out on me (possibly confirmed with the above codes)

-Also could be the fuel pump overheating and crapping out on me.

I've hooked up a fuel pressure guage to see what the pressure's doing when it cuts out. Fuel pressure looks fine at 37-38 psi, dorpping a little with light throttle blips. So far, after dogging the crap out of my car, I haven't been able to make the thing die. I figgured if fuel pressure looked ok, I would just replace the module, and if fuel pressure dropped, I would replace the relay and see if it cured the problem. I've got both parts in the tool box in my car so I can do the repair immediately.

Anyway, does anyone have any thoughts? I'm going to go ahead and replace the TFI module and keep the original as a spare, but I don't want to replace the module until I'm sure it's the problem (i.e. it dies, I repalce the module immediately and it runs fine). I just want to narrow it down and make sure I have the right problem.

Thanks for any ideas!

--nathan

[PKRWUD]

Sounds like your EGR valve is sticking open slightly to me, but it could also be your relay. I seriously doubt it's your module. They go bad from heat, but they tend to function more like a light switch; either on or off. You really need to duplicate the problem and see what the pressure does. If it dies, it's your relay.

You could also disconnect and plug the vacuum hose to the EGR and see if that makes a difference. if it does, replace the EGR.

Take care,
~Chris

[silver_pilate]

Thanks for the ideas. I'll definately keep an eye on the EGR. I'm going to run it hard again today. Hopefully the clouds will burn off and it will warm up. Like you said, I really want to isolate the problem before I start replacing stuff. But it seems that it only happens when you least want it to. Such as right in the middle of a four lane street with traffic backed up for four blocks at a stop light in the middle of a Saturday afternoon shopping crowd. Luckily it started up right after it died and I made it off the street before it conked out for good.

Oh, and by the way. I had a "DOH" moment. I somehow forgot, when I was reading the codes, that I had purposely pulled the fuel pump relay out while the car was running to see if it mimicked my problems. That's when those codes were probably stored. Sometimes I wonder about myself.

--nathan

[PKRWUD]

Originally posted by silver_pilate
Oh, and by the way. I had a "DOH" moment. I somehow forgot, when I was reading the codes, that I had purposely pulled the fuel pump relay out while the car was running to see if it mimicked my problems. That's when those codes were probably stored. Sometimes I wonder about myself.

--nathan

You're one of those guys that always ends up with a box full of extra parts when you're done, huh?



How've you been Nathan? Well, I hope!



Take care,
~Chris

[silver_pilate]

Hehe...

Funny thing is, I usually don't end up with any extra parts. In fact, sometimes I end up not having enough! Actually, I took off the dash to replace the heater core, and when it was all back together, I had exactly the right number of screws with none left over somehow. I impressed myself.

I've been doing pretty good, Chris; thanks for asking. Really, really busy with school, but I'm just finishing a couple of weeks off that was much needed. I start up again Thursday. I'll finally be done with classes in December. Hope your business hopping along.

Anyway, I ran the car all over today. Not a hiccup. Frustrating. Luckily I don't have anything larger than target load for the 12 guage. Course, the .45 might be pretty satisfying.

I'll likely just end up replacing the TFI for good measure (already have the part) and just drive it to Amarillo for a week to see if something happens. Hopefully when it does, I can narrow it down and fix it.

So...so far we have possible pump relay, maybe an EGR valve, possibly a TFI starting to go, maybe a fuel pump overheating, perhaps a coil going south. Any other ideas? I figure it's heat related because it's only happened after long drives, and it starts again when it cools down. But then again, I've got the engine plenty hot the last couple of days and no bananas.

Guess I just have to wait until it happens again and see what the fuel pressure does to rule the fuel system out.

--nathan

[PKRWUD]

Nathan, I was just kidding. You've always been quite meticulous, and I actually would be very surprised to hear that you had as much as an extra washer left over after a complete overhaul.


To help you with your possibilities, let me tell you why I think what I do;

The TFI does go bad, and is effected by heat, but it is very unusual for it to cause the vehicle to sputter for a while. When they start to head south, they act just like a circuit breaker; when they get hot enough, the open the circuit like a switch. When they cool sufficiently, the circuit closes again. I think replacing it is a good idea, but if you had done that 2 days ago, you would now be thinking you fixed the problem, because it hasn't happened again, and you'd stand a good chance of getting stuck somewhere, wishing you were armed.

The coil is another possibility, but I doubt it. When the ignition coil starts to go bad, it usually acts like a rev limiter. Rather than kill the engine, it limits your rpms. It may run great up till 3k rpms, and then falls flat.

The fuel pump relay is a good possibility, but they aren't effected as much by heat as they are by amps. Over time, metal transfers to the contacts inside, and they get "sticky". Eventually, the relay either get's stuck open, or stuck closed. Still, like anything electrical, there is increased resistance when it gets hot, so if it's thinking about failing, it will be most likely to when hot.

The EGR valve is supposed to be closed at idle, but is open when you are cruising on the highway, or at a steady speed. Since the EGR valve allows exhaust to pass through it, soot and other exhaust crap settles on the valve, making it more likely to stick open, even if it's just a little bit. If your stalling problem happens most often after driving on the highway, or at sustained speeds, and then exiting, what may be happening is that the EGR is open for quite a while, and when you exit, and it should be closed, it sticks open slightly, allowing exhaust to lean out your mixture to the point of stalling. After it cools, and the metal contracts slightly, it overcomes it's "stickyness", and closes.

This is really just an educated guess, since I can't check it out in person, but from what you've told me so far, it sounds more and more like the EGR. See, this also explains why just getting it hot won't make it act up. It needs to get hot, and spend some time at highway speeds.

Did that help any?

[QuantumMotorsports]

Sounds like it's just another case of ford electronics being bastards. Man, I've had three 5.0 EFI cars and ALL of them did stupid stuff like this. One wouldn't idle at a steady RPM, I checked and/or replaced everything I could think of, O2, Idle air valve, TPS, EGR, TFI, Coil, Timing, ignition pickup in the distributor, etc. Then the same car would start hesitating and stuff. My next car would just randomly die while sitting at a stop light. Or right as I would hit the gas to leave a stop light, it would die. The only way it would restart is if I cranked it with the pedal to the floor and it would start. Finally figured out that was my TFI was messed up and the only way to make it fire was when it thought it was at WOT. Anyway, your problem sounds a lot like either the TFI or I've had the pickup coil in the distributor go out and it does things like what yours is doing. When it got hot, it would sputter and die. Then sometimes restart, sometimes not. If it cooled off most of the time it would start again. I finally just replaced the whole distributor because the bearing was all sloppy in it anyway. Well, I hope you enjoyed reading that little novel that I wrote. Good luck man!!!

[silver_pilate]

Thanks for all of the replies.

I replaced the TFI module last night. It was the original from the factory. Still had the green grease mark on the back 140,000 miles later. I figured it sure couldn't hurt anything to have a new one in.

Anyway, I'm going to take the car to Amarillo today through Saturday. About 90 miles of highway driving. If it's the EGR, maybe it will stick open, and if it the fuel pump relay, I've got a spare.

Chris, thanks for the explanations. I was curious as to why the EGR might cause the problem, and the other reasonings were helpful. If the car stalls out again, is there any way I can diagnose it as the EGR? Beat the crap out of it with a wrench and see if it pops shut? I assume plugging the vacuum line after the valve is already stuck would be a mute point and would only serve as a preventative measure?

As far as coming up with extra parts...after the rebuild I somehow ended up with a pair of extra cylinder heads, a cam, and an intake.

--nathan

[PKRWUD]

Originally posted by silver_pilate
Thanks for all of the replies.

I replaced the TFI module last night. It was the original from the factory. Still had the green grease mark on the back 140,000 miles later. I figured it sure couldn't hurt anything to have a new one in.

Anyway, I'm going to take the car to Amarillo today through Saturday. About 90 miles of highway driving. If it's the EGR, maybe it will stick open, and if it the fuel pump relay, I've got a spare.

Chris, thanks for the explanations. I was curious as to why the EGR might cause the problem, and the other reasonings were helpful. If the car stalls out again, is there any way I can diagnose it as the EGR? Beat the crap out of it with a wrench and see if it pops shut? I assume plugging the vacuum line after the valve is already stuck would be a mute point and would only serve as a preventative measure?

As far as coming up with extra parts...after the rebuild I somehow ended up with a pair of extra cylinder heads, a cam, and an intake.

--nathan

The best thing to do if the egr sticks open is to either let it cool so it closes, or attach a hand vacuum pump to it, and repeatedly apply and release vacuum, trying to unstick it.

Beating the crap out of it might work too, honestly, not to mention the tension you would release at the same time!

Take care,
~Chris

[silver_pilate]

Well, I'm pissed and relieved at the same time.

Drove it to Amarillo tonight (just got in), and sure enough, after over an hour of trouble free highway driving, it ran rough at the first stoplight died at the next. I was able to get it going long enough to get to a parking lot off the road.

I popped the hood and the first thing I did was look at the fuel pressure on the mechanical test guage I've got hooked up. It was zero. I tried swapping the pump relay out: no cookies. So I let it sit a few minutes, turned the key several times to cycle the fuel pump, and it sounded a little high in pitch. It wasn't building pressure either. So I let it sit a few more minutes and cylced the pumps again until I heard it sound more nomral. The guage showed just about 40 psi. I then started the car, and jumped out to watch the guage. It sat just fine at 38 psi, then started to drop, drop, stumble, drop, die.

So I sat in a parking lot 3 miles from my appartment for 50 minutes to let the pump cool. I started it up and drove it in.

So, it IS fuel related, and is probably the pump. It's a relief to know this, but I'm pissed because the pump's not much more than a year old. My guess is it's overheating, but is able to run while under throttle with the regulator opened up. When it drops to idle and has to work harder after an hour of highway time, it poops out?

The car has had two brand new fuel filters on it in the last month. It's occured before and after filter changes, so it's not the fuel filter clogging up. When I get the thing back home, I'll first check all the fuel lines from the tank to the rails and make sure there are no dents or kinks restricting flow. Next, I'll blow out the lines with compressed air. Then I'll drop the tank, pull the pump and check it out, and clean the tank. My best guess is that I'll need a new pump? Probably go with a 255lph (up from 190) as I may run the spray in the future.

What do you think? Any other things I need to look at? Suggestions? I also got a great deal from a buddy for a spanking new BBK adjustable regulator and practically new 30# injectors ($200 total...how can you pass that up?). I'll put these on as well.

Thanks for your help and patience as I attempt not to junk-yard the car or sell it to John. Hehe....

I eagerly sit and await your responses...please, please, one at a time. Try and contain yourselves.
--nathan

[84gt347]

pick me pick me me first. Ready for this suggestion? Sell it to john. Have you gotten the rest of your shopping for gears and a posi rebuild yet????? I didnt think so. Buy a ring filer and a master gasket set and a compucar 120 shot. Leave it with me for a couple weeks.

[PKRWUD]

Well, your results certainly point to the pump. Although I've never heard of one going out quite like that, I don't know what else it could be.

Take care,
~Chris

[silver_pilate]

Well...put in a new Holly 190lph. Had a sweet deal on a 255lph but the guy sold it an hour before I called him back. Anyway, we blew compressed air through the feed fuel line and checked out the lines and everything looks good. I lit a match so that I could see inside the tank (well, ok. not really) and it looked clean. No crap on the bottom or floating anywhere that I could see. Filter is new.

When looking at the pump I pulled out compared to the new one, it just looks old. Kinda like it was on a shelf for a couple of years before I got it. The mechanicals on it are different and the power hook ups are different. The Holly (although both pumps were made by Walbro) just looks more modern. Anyhow, got it in and turned the key a few times. There's a pretty distinct difference in the sound. The new pump is much lower and quiet enough that you have to purposely listen for it. The older pump always sounded like my stock pump that was going out, just much quieter. Pressure built up fine and all looks well.

Just got in from driving back from Amarillo. It's hot today, suppose to get to 100 and the car is running just a tiny tad warm. Anyhow, first stop light...

....

....

Isn't the suspense killing you....

....


All was well. Didn't die on me. Pump still sounds great and holds steady pressure. Drove through town and so far it runs fine.

Maybe I just had a bad pump or it had a filing in it or something. Who knows. Just have to drive it some more and hope that did it. Thanks for all the help. New injectors and adjustable regulator are going in next weekend along with new tires.

Sorry, John. Maybe I won't sell it just yet.

--nathan

[PKRWUD]

Doesn't it feel great when you figure it out and fix it yourself!

Great job, Nathan!

Take care,
~Chris

[andrea_fiveoh]

i've been having the same problems for the past year.
and i've replaced everything but the fuel pump.
after reading nathan's post i finally got my mechanic to check
the pump. the pressure is fine @ idle he let it idle for about
an hour but i guess it's not the same as driving it on the
highway bit since my GT has the exact same problem i told
my mechanic to go ahead with the pump.
I just got it back today ang I could hardly hear the pump
priming and not at all while running. I've always thought
that the pump should always be audible.
well I hope this solves the problem. i would also like
to thank you all for hopefully ending this inconvenience I could finally cruise around my GT this summer

[silver_pilate]

Well, I'm glad we could help, and I hope it solves your problems. I know it sucks to not know if you can depend on your car. I tried running the dog out of mine to make the problem occur again and had absolutely no luck. I let it idle for ever, ran it hard, ran it slow, ran it long...not a stumble. It took that long haul of highway driving for mine to crap out.

Anyway, so far so good on my car. I'll find out for sure probably tomorrow when I head back up to Amarillo.

I've still got the old pump as a reminder...and the thing rattles. Kinda like there's a tiny little ball bearing shaking around in there. Are they suppose to do that??

Chris and everyone else (except for John...well, ok. John, you too), thanks for letting me bounce ideas off your skulls. Hope we got it licked.

--nathan