Problems after long idle

[Black91SHO]

I have a strange problem that's recently popped up. I tow my '91 SHO behind vehicles that I deliver, then I unhook my car and drive it home. I tow it with the engine idling, because if I don't, I have to replace the rack & pinion about once a year, and that got old real fast. This was all fine till recently.

When I reach a destination and unhook my car after it's been towed while idling for several hours, I turn it off. Then, when I go to turn it on again, it won't idle. So I rev it a few times and it idles a little low and slightly rough. I rev it a few more times or drive it and the problem stops. It's not a big deal now, but it's never done this in the past, which tells me something's not working properly. I fuel pump sounds weird, and if you hit the fuel tank, it quiets down for a few seconds. It's strange.

So I went ahead and replaced the fuel pump and fuel pump assembly. Does the same thing and the fuel pump still sounds odd.

Can anyone think of a good reason this might be happening? I'm at a loss...

 

[rubydist]

how much fuel was in the tank that first time it started acting up?

 

[Black91SHO]

There's always plenty of fuel in the tank. It's happened with anywhere from 1/4 to nearly full.

 

[rubydist]

I was just wondering if the fuel level was low enough that it got warmed up enough that it damaged the pump. At idle, nearly all of the fuel is returned to the tank, but it does get heated somewhat in the process, so after hours of idling, it might be warm enough to cause a problem, I dunno.

 

[Black91SHO]

I suppose that's a possibility, but if I made a product that could overheat idling, I might have to leave the manufacturing industry.

What would cause the overheating fuel pump?

 

[sperold]

Clean the Idle Air Control (IAC) for a start and see if anything changes.

 

[rubydist]

the fuel pump is cooled by the fuel in the tank - that is why if one runs out of gas, nearly always the fuel pump will fail in the next few months. when idling, the pump is sending way too much fuel to the engine, so it is mostly returned to the tank. this returned fuel has been heated by bypassing the pressure regulator. if the fuel level is low enough, and if the fuel is heated enough, it is possible that the pump is no longer cooled adequately. once the fuel pump is damaged, the pump motor bearings will be such that it will heat up faster the next time. eventually, maybe it becomes a problem. I don't know if that is what is going on, but its the only thing that I can think of.

 

[luigisho]

Just curious, you have the front wheels off the ground when towing the car?

 

[sperold]

You are not going to get a lot of airflow through the rad as you are being towed by a vehicle that is very close to you. For that reason, your rad fan will be doing most of the cooling. So everything will be well heat-soaked, as there is not really much of a breeze to clear the engine bay.

Where is the heat gauge needle when you first jump in the car to shut if off, and restart?

When things get hot, they start acting up, especially the electroic stuff, your underhood temperature might get pretty high.

I would prop the hood partly open to start with and see if the situation gets better.
I would also look into a remote start. I would run the engine when the road gets twisty, and shut it off on the long highway miles.
Maybe try the coolest thermostat you can find so the engine runs as cool as it can.
Try and dream up a fabbed scoop affair to pull more air up from the road (from under your tow vehicle) to see if you can keep the fans from coming on so much.

 

[Black91SHO]

The IAC valve is pretty new, so I haven't bothered checking that yet. Also, if it were the IAC, it would be happening on occasions when I haven't been towing it.

No, I'm not towing it with the front wheels off the ground. All four wheels are on the grown, which means I need the power steering pump to work so it doesn't wear out my steering rack. I had to replace two of them before I realized I needed to idle the car while towing to keep them from going bad.

Thanks for the info Rubydist. It's an interesting theory. But I haven't had the tank below half a tank since I got the new fuel pump a week ago, and yet it still does it. So I'm guessing that's not the problem.

 

[luigisho]

I was thinking maybe if the car was on a full sized trailer-- maybe the front suspension wouldn't take alot of abuse and it wouldn't need to be running to save the rack.

Since all 4 are on the ground would a front end tow dolly relieve the movement up front?

 

[Black91SHO]

Sperold,

Thanks for the info. he car is lowered quite a bit in the front, and therefore close to the ground, and the vehicles I tow it behind are box trucks usually that are up off the ground, so quite a bit of air passes under them. Also, I have the double-core radiator mod on the car, so the temperature is fairly low when I check it during or after a tow. Temperature isn't going to be the culprit in this case, but it was a good thought, though.

 

[Black91SHO]

I was thinking maybe if the car was on a full sized trailer-- maybe the front suspension wouldn't take alot of abuse and it wouldn't need to be running to save the rack.

Since all 4 are on the ground would a front end tow dolly relieve the movement up front?

I had a tow dolly at one point and it was a huge pain, and got stolen eventually, too. Now, I'm in a situation that would make it even more of a monumental pain, so I just choose not to bother with that type of thing anymore. And trailering the car is even more of a pain. Towing four-down is the best way I've found for my situation, and it hasn't been a problem for several years now. But recently, this idle issue popped up and it's got me stumped. Thanks for the idea, though.

 

[zoomlater]

Were there any codes after the last time this happened?
Can you describe what the fuel pump sound is like, is it like a squeal?
Did you check the fuel pressure after the restart?


Is this the same car that you previously had the idle issue or is this a different one?
http://www.shoforum.com/index.php?threads/idle-issues.129563/

 

[SHOtimer]

Interesting problem, both of them.

1. I don't know see how towing your car would **** the racks so quickly. I would be more concerned with motor wear/tear with all that idling while you are towing it everywhere. Reman'd racks are a crap shoot anyway, you may have just gotten two bad ones. How did you determine they were bad?

2. I think the problem you are experiencing with the poor idle after re-start is a classic failure of the fuel return line check valve.

 

[Black91SHO]

No codes.
Fuel pump doesn't squeal, but I can't really describe the sound.
No, I didn't check the fuel pressure. No gauge or tool to do so.
It's getting pretty decent gas mileage, too.
No, not the same car. That was my other '91.

1. The racks were bad, because they would start leaking eventually (the seals were going out) and because there were metal shavings in the power steering fluid--a lot of metal shavings. So the pressure being pushed through the rack while being towed was putting a lot of stress on the seals, which had no circulating fluid, and the gears were grinding without circulation of fluid, causing them to flake off little bits of metal.

2. That's interesting. I'll try replacing that. That actually sounds like it could be the culprit.

What are the symptoms of a failed fuel line return check valve?

 

[SHOtimer]

You've been here since 2003, you know how to use the search function!

I dug up a good old one where spdatt did some explaining....
http://www.shoforum.com/index.php?threads/fuel-pump-check-valve.55122/#post-513862

I have also found with a bad return line check valve, once the motor starts it runs rough for the first approx 10 seconds until the hot fuel is run out of the rails.

 

[Black91SHO]

Thanks.

I just replaced the entire fuel pump assembly, which includes the return check valve. So I'm guessing that's not the problem, unless the brand new one I got was bad.

Hmmm...

 

[itwonder]

I would discontinue idling for hours on end. Nothing good can come of it. I doubt your rack problems are related to towing, as long as you tow with the steering wheel unlocked ;-). Once you have a rack failure and get metal particles in the system, it can damage replacement racks. Install a Magnafine filter in the return line to take care of that.

 

[Pintony]

This is how I fixed that problem.

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