Cycokat

1985 LB9 Z28 w/TPI

It will run fine for a little while (20-30 mins.) and then sputter and die. Today I put my fuel pressure gauge on it and let it run until it stalled.

Key forward, goes to 42 PSI then the slow bleed off. Started it sits at 35/36 and will change with throttle.

When it stalls the pressure dropped to 16. It slowly crept back to 20. I waited a few minutes to try again. Key forward, pressure to 42 PSI, engine starts and nearly immediately (10 seconds?) stalls. Fuel pressure to 0 this time.

Waiting a few minutes, key forward, pressure to 42. Engine starts for maybe a second or two. Pressure to 0. After this, the fuel pump will not prime and give me any pressure with the key forward. If I wait a while, I can make this cycle repeat. When it starts, it is always between 20 and 30 minutes that it stalls for the first time.

Is my fuel pump bad? I'm not a mechanic but to me it is weird that it will seem fine if I wait a bit. I'm not a mechanic and know enough to be dangerous, stupid or sometimes both. Any thoughts are appreciated.

Tuned Performance

iTrader: (92)

If the pump doesn't prime when warm,the pump is bad or there is an issue at the relay .

Cycokat

Thanks. Is the relay still in play after the car is started? I thought the relay was only for the initial prime to get the pressure up to start the engine. Like I said, I'm not a mechanic though.

Tuned Performance

iTrader: (92)

The relay is for the initial 2 second prime before starting. The oil pressure switch then takes over during cranking to supply the pump with 12v.

GeneralDisorder

iTrader: (1)

Jumper the relay out of the equation- just connect the orange and tan (large) wires going into the relay connector with a jumper lead and run it like that. See if it still dies. You may have a heat sensitive electronic component. The ECM on the older MAF cars was prone to circuit board cracks. Such a failure may result in a failure once the board heats up. Distributor pickups can do this as well - when the ECM doesn't see the pulse from the distributor pickup it will shut off the fuel pump. This feature is designed to prevent the pump from running after a collision, etc.

Rick

Cycokat

I haven't been able to play around with this for a while. In trying to isolate, I ran it until it died again with the relay power jumped. However now, the pump does not prime at all. I think it is dead. I checked the power back at the connector near the tank and still have 12v. I also saw this article on Austin Third Gen where it talks about checking the resistance in the pump. Mine read 24.5 ohms which is just a smidge over the 20 ohm threshold stated in that article. Both of these things point to a dead pump, but I would hate to do that job and then it still not start.

Is this enough info to convince you that my pump has died?

Also, as an added bonus, I may have leaky injectors. I had someone turn the key and clamped of the feed and return lines and the pressure still dropped slowly.

Thanks for any further thoughts on this. \m/ >.< \m/

Cycokat

Did I say something wrong? Or have I proven to be too much of an idiot to warrant a response to my question? I don't ping the group for much, or very often, but considering how little I really know they help is appreciated.

TTOP350

iTrader: (8)

Change fuel filter and fuel pump.

Tuned Performance

iTrader: (92)

Cycokat

Thanks for the response. I guess I was hoping someone would tell me it was something other than the pump.

TTOP350

iTrader: (8)

Fuelpump failure denial....... We've all been there.

GeneralDisorder

iTrader: (1)

You can try to power the pump by manually giving it 12v through it's connector. But it probably is going to have to be swapped. As a further test you can sometimes pull fuel through a dead pump using an external pump and try running it like that to see if it still stalls.

Really though - a new pump is a good feeling.

GD

paulo57509

So far, the only time this happened to me there was a factory access panel in the trunk.

When you replace the pump, please don't cut a hole in the floor to do it.

Cycokat

Denial. That sounds about right. And paulo, I don't plan on cutting the floor. Thanks again for the input everyone.

Cycokat

I know, no one asked for an update, but you are getting one anyway. The pump is in and that appears to have been the culprit for my stalling. I will not be sorry if I never have to do that again though.

I finally got everything out only to see that someone previously had cut the floor to get at the pump. This was right after a looong wrestling match with my tank to get it out.

Fingers crossed that this one has a long life.

Thanks folks.

NoEmissions84TA

iTrader: (1)

You might also check that your tank is venting properly.