Chris Lockhart

OK folks, I am trying to diagnose a VERY bad surging problem with my '89 GT. On Greg Nichol's Tip Site there were some tips about the possibility of a bad in tank pump. I had always thought that I had only the external pump, but it was stated that all GT's and GTS's have the in tank pump also. Supposedly, the failure of the in tank pump can cause some lean running issues (which I have had) and then as the external pump starts to act up, the surging problems crop up. This sounds reasonable, and I intend to put the fuel pressure guage on it on Tuesday. (my guage is busted, so I have to get one from work) If I do need to replace the in-tank pump, where is it located exactly??? Is it the unit I see just forward of the external (green) pump, in the sump area of the tank??? TIA,

worf928

Follow the rubber input line to the main pump towards the tank and you'll find the fitting for the in-tank pump. You'll barely be able to see it. To R&R you need to have an empty tank and loose the straps the hold the tank in place.

cfc928gt

Chris,
I have both pumps out on my '89 GT right now, both were dead. I used a 35mm socket to get the in-tank pump out, like Dave said, you just need to lower the strap a bit. I took the back two bolts out and losened the two front bolts. Your external pump might be bad but I don't think you'll normally get the surging you speak of with just the outside pump working.

Bill Ball

Chris - Vacuum leak is more likely cause, isn't it?

drnick

is it possible to run with only one pump? ie remove one or other. why do they have two?

Vilhuer

In-tank pump helps to bring fuel to main pump on hot climates during startup when fuel in engine bay lines has vaporized and created vapour lock. It will not do much to overall delivery rate of main pump.

Earl Gillstrom

Hi Chris,

The problem as you describe it sounds like the in tank pump or the hose between the in tank pump and the fitting that screws into the tank. Porsche had a problem with that hose desintegrating. I thought that it only affected 1990 or 1991 and later cars, but could have affected 1989 models. There is a screen filter before the in-tank pump. If the hose desintegrates, then you not only have no in-tank pump but suck all the dirt in the tank into the external pump. When my hose desintegrated, I had the symptoms that you describe. I think you have enough miles on your car that it would be worthwhile to replace both pumps as well as all hoses. Do the job outside and be very careful as you have to drain all the gas out of the tank.

cfc928gt

I called the in-tank pump supplier. They said it delivers 5 - 6 psi and can pump 60 gallons per hour. Truely nothing but a helper pump. When I drained my tank, which was 3/4 full, I just pulled the hose between the pumped and let it drain into a gas can. Took twenty minutes to let gravity drain 2 1/2 gallons thru the inoperable in-tank pump. The outside pump was working too hard which is probably why it failed.

ew928

Anyone converted the dual pump to single external pump?
Replace the intank pump with the mesh screen filter on the 928's that
came only with single pump.

Chris, remove the plastic panel over the fuel tank. If you see 2 wires coming
out of the tank outlet, you've got the internal pump.

Did you ever get the rear tires to point in the direction you want?

Ernest (NYC)
Don't spill that gas. T'was 3.29 premium in New Joisey.

fst951

I would replace both pumps if you are in doubt and are sure it is a delivery issue.

I have replaced just one and several days later had them die again.

Thanks,

Garrity

cfc928gt

Chris, did you ever find another 18" rear wheel to match the one that got wrecked?

Chris Lockhart

Thanks for the input guys. That helps alot. I thought the component I was looking at was the in-tank pump, but I wanted to be sure. Like I said, I will have to wait until tomorrow evening to check the fuel pressure, but from all of my reading, this seems the likely culprit. As best as I can tell from the records I have on the car, both pumps are original from June of '89.

Ernie, the left rear still has some unwanted negative camber, but it doesn't affect the handling. Basically just a wear issue. I'm wearing both rear away on burnouts anyway, so it hasn't made much difference. LOL.

CFC, I still haven't found a replacement wheel, but I really haven't been looking. Just been driving the hell out of her!!!!! What a wonderful car.

Thanks again for all the input. (hope you're doing well Capt Earl !!!!)

Chris Lockhart

Had the Calibration Shop at work fix my VDO fuel pressure gauge today, and installed it when I got home. The car has roughly 60 psi at idle. When giving it more throttle in neutral, it seems to be smooth as glass. Take it out on the road however, and under load, it surges horribly. I'm planning to look at possible vacuum leaks like Bill suggested. After that, I'm kinda lost. I plan to start another thread on my issue. Thanks again to all who responded.

worf928

If you have stock dampeners and regulator then that idle pressure is too high. It should be ~45 PSI with a rise to ~55 PSI (IIRC) during throttle plate opening. You're high idle pressure could be due to no vacuum to your dampeners and regulator. Disconnect the vacuum line to the dampener at the front, hook a vacuum gauge to the line and see if it you get vacuum. If not, I'd check the 5-way vacuum fitting on the driver's side of the MAS. Use an inspection mirror to see if the long line to the connector is plugged in to the vacuum port on the top of the throttle body.

Chris Lockhart

Hey Dave. The 60 psi is where I set it with the RRAFPR. It's been there for 4 years with no ill effects.

BTW, I may be trying to pull the hall sensor this weekend. The connector is toast, so I may solder it direct, and lengthen the leads some to make it more accesible.