Hot Starting Issues

[wcc]

When I start my '85 911 when it's cold (hasn't run in a few days) it fires right up. Everything is good. Then I drive it a little while and it's all warmed up to normal temp. I park it and let it sit for a little while and when I come back to start the warmed up engine it cranks for a little while and then with a second turn of the key it'll fire up pretty quickly. Can you guys help me out with what's wrong here?

I was thinking it was the pressure regulator here:
http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_FULmot_pg4.htm#item17

But I just wanted some feedback and some ideas before I start spending money on parts that don't need to be replaced.

Thanks in advance for your help!

[Breeang]

Bump

[charlesbahn]

Almost certainly fuel pump with integral check valve needs replacing, although there are a few other remote possibilites (bad DME brain (soldered connections), DME relay, fuel pump relay, alarm/fuel shut off brain), etc.).

[wcc]

Originally posted by charlesbahn
Almost certainly fuel pump with integral check valve needs replacing, although there are a few other remote possibilites (bad DME brain (soldered connections), DME relay, fuel pump relay, alarm/fuel shut off brain), etc.).

Are you saying replace the fuel pump and the check valve or is it one unit?

Is there any way to check some of the parts before I start replacing them?

Fuel pump $192
Fuel pump check valve $17
DME Relay $31
Fuel Pump Relay $27
Fuel pressure regulator $83

So I'll replace the check valve, DME Relay and Fuel pump Relay for something like $75 dollars. Do you think that'll fix it?

[charlesbahn]

The problem is the check valve. But the 1985 model has the check valve integral to the fuel pump and they must be replaced as a unit (unless someone with more knowledge than I knows how to separate them). On earlier models the check valve was separate and could be replaced separately for less $.

You can also add a check valve after the fuel pump, but I'm not sure that's such a good idea for the next owner/mechanic won't know where it is and it's non-stock.

Most of us carry spare DME relays and fuel pump relays in the glove box, these are good to have, and with spares you can always quickly replace them and see if it helps.

BUT its almost always the fuel pump/check valve and it will cost you $192. If you're not in a hurry, get the relays and try them, but I'm pretty sure you'll end up getting the fuel pump also.

Doubt its the pressure regulator unless you have a gas leak that you can smell (they have a diaphram that goes).

[wcc]

Now I'm confused one the pump and check valve thing. Our host has the pump with the check valve and down the page a little bit they have just the check valve for the same years (84-89).
Here:
http://www.pelicanparts.com/catalog/shopcart/911M/POR_911M_FULmot_pg2.htm#item10

Ok, I suppose it wouldn't hurt to have those relays as a backup. So I'll pick them up anyways.

I don't smell any gas so I'll forget about the regulator.

[charlesbahn]

You're right about the on line catalog- not sure if the separate check valve will work or not, when mine went bad I was told I should replace the whole unit (that did solve the hot no start). Maybe someone else will chime in, or you could call Pelican and ask them.

[Wil Ferch]

This is not systematic troubleshooting...more like shootong in the dark....

It could be a bad injector that "bleeds down" and doesn't hold system pressure..it "could" be a bad fuel pump or check valve..it could be a number of things.... fuel pressure regulator or damper too.....

I think the poster is looking for more solid information than "it almost certainly" is the fuel pump..... it also "can be " the start of a big and costly fishing trip.....when no diagnostics are done.

IMHO....

Wil

[wcc]

Wil,
you are right and I feel like I am shooting in the dark. I would like to do a systematic diagnostic, but how and where to start? I've read through the searches that the best way to check a relay is to replace it with a known good one.

How do I check the fuel pressure to make sure the check valve is holding the pressure?

How can I check the pump to see if it's pumping enough pressure?

How do I check the pressure regulator to make sure it isn't reliving the pressure somehow?

How would I check the injector?

Are these items that can be checked by doing a test on them or do I have replace the part to see if my old one didn't work? As you can see I haven't even started and I don't know where to start. I know it "could" be a ton of things, but I guess I was hoping that a higher percent of people say that they replaced part "X" and it fixed the problem and a few say it was something else. Well I would start by replacing the part that "most" people say is the problem.

[Wil Ferch]

Wcc:

I'm afraid I can't offer something more constructive...but the "approach" seems wrong...as to advice you're being given.

Either the factory manual...or the Bentley manual should/can offer a chronology of things to look for / check....

I'm away from my info sources as I write this..but maybe someone has access to these manuals and offer interim advice....

Wil

[wcc]

I'll check out that Bentley manual when I get home tonight and see what they say about it.

[jdowty3]

The pics in the catalog and the fact that the check valve is available seperately leads me think you can replace just the check valve. At $16.25 for the check valve, it may be worth replacing it to see if it fixes the problem.
Does the Pressure regulator on a 3.2 work similar to the Fuel Accumulator on 3.0 and hold the fuel pressure in the lines close to the motor?

[wcc]

Yes the regulator is up by the motor:



It isn't the cost of one thing but the total of all the parts that may or may not be the problem. I would rather replace the part that is causing the problem instead of replacing a ton of parts that may or may not fix the problem. That's all.

[Wil Ferch]

Grady.... ummm....this is a DME car.... not a CIS car....

The CIS cars usually ( also) have the external-only check valve on the fuel pump...and I *vaguely* recall someone trying such a fix on a DME car that uses a fuel pump with integral check valve. In essence, you'd have two check valves in series. Forgot how well this was reported to work....

Cheers,
- Wil

[Grady Clay]

Wil,

You are correct. After I wrote that up I went and checked the year and didn’t intend to post it. I must have hit the wrong button. I’ll delete it.

Thanks,
Grady

[Wil Ferch]

Grady:

I hope you understand that I respect you greatly...and this "correction" was only meant to set the archived responses properly....

Thank you for not taking this incorrectly or personally.... an issue that unfortunately, I continue to do battle with on a "net" forum.....

- Wil

[wcc]

After reading a bunch of stuff from the Bentley manual last night. I've concluded that the relays I can test with a multimeter to see if connections are getting power. As for the fuel itself I need to pick up a fuel pressure gauge that hooks up to the rail. From that I can check the regulator, pump and check valve. However that tool from what I've found was $200. I couldn't find it from our host, but before I order it I'll call and ask PP. Any other suggestions for the tool? Anyways, for that price I could replace all kinds of stuff.

Grady - No harm no foul.

[jdowty3]

I'm not suggesting replacing the pressure regulator with out more diagnostic testing but $16 for a check valve may be worth doing first. I just replaced the check valve on my SC. The only hard part was getting the cap nut that goes over the long part of the check valve off.
Maybe someone at the swap meet this weekend can offer advice.