1970 911E warm start problems

[Gasman59]

Hi All:

I searched around and did not find anything significant for my problem. Here is the description:

Cold start, hand throttle up, fires right up and runs fine.
Hot start, Full throttle, fires right up and again OK.

Warm start, having sat for a few hours after driving. Crank, no throttle stumbles at about 150 RPM and stalls, full throttle, nothing except after many attempts at no throttle/full throttle it stumbles, pops, and finally revs up and is OK (full throttle). I am now thankful for the two batteries).

I have checked the enrichment solenoid and it works, cleaned the enrichment pipes and "Jets".

I do not know if the temp/time sensor is working properly. I cannot find a source for these to try.

Any suggestions?

Thanks in advance,
Ron Young

[sessa]

Sounds like an issue I had a year or so ago. It turned out to be a fuel pump that was on it's last legs and unable to deal with the vapor lock that had been created from the car sitting. If you do a search there are ways of testing you fuel pressure.

[Gasman59]

Paul, thanks for your response.

The fuel pump is new (Not rebuilt but a ridiculously expensive new Bosch pump). Old one was leaking.

I did not consider vapor lock. I will look for the threads regarding pressure/flow testing. Can this occur considering the return flow from the engine area to the fuel tank? (MFI)

And, yes the fuel filter is new. The old one, which I think was original based on no mention in the service records, (50K car), was clogged. I replaced it along with the new pump.

Thanks, Ron

[bkreigsr]

my 73 always balks when hot if the dwell angle is off a couple of fractions, assuming the points are not pitted. does your tach needle bounce at all?

[Zeke]

I think you're on the right track about the temp sensor. One way to find out for sure is to double check the cold start circuit visually under the exact conditions you experience the difficult starts.

I'm not going to suggest how to do this, but two people would make it a lot easier. The reason I won't go any further is because if there is a backfire and a flash, I don't want to be the guy that said stick your head in there. Use some caution. Always have an extinguisher nearby.

Or take it to someone that can test it properly.

[Gasman59]

Milt, thanks for the tip. I do have a lamp setup that I used to check the cold start solenoid. Brain fart I guess, I will bring it along with me and hook it up next time she acts up.
Takes about 30 seconds.

I have heard that some folks bypass the whole circuit and wire a push button to the solenoid as a form of manual enrichment device. Might be my last resort.

Do you know of a source for the temp switch?

Thanks, Ron

[Gavin English]

Ron,

I see that you live in "Northern NJ". I am a new owner of a 1971 911E. I live in Dumont. (Bergen County) We should compare notes. I have similar problems with my car.

Gavin

[blucille]

yeah, me too...I'm in Haworth, have a 1969 911S, a couple other vintage european cars filling up my 200 year old barn, complete with a 2 post lift....should have heat by winter...maybe we should all meet up at the NY/NJ run that starts at exit 5 on the palisades.

-Lewis

[Gasman59]

Hello Fellow Jerseyan's:

FYI, I am just outside of Morristown. I went the pushbutton route using a relay wired into the starter circuit so it will only open the enrichment solenoid on demand and only when the starter is running.

I just finished a 700 mile trip with the wife to my sister's wedding. Car was flawless and the "Button Mod" works perfectly.

A heated garage with a lift! I am jealous!

Best Wishes,
Ron Young

1970 Porsche 911E Targa
1973 Jaguar V12 E-Type OTS
1985 Mercedes 300 Turbo Diesel (high 30 MPG beater)
2005 Ram 2500 (Crummy MPG)

[dafischer]

Looks like a potential NJ MFI support group here!

[Gavin English]

Hey Lewis,

I was out last night in my 911E for dinner at Adiamo's. It sounds like you have a nice set up for a garage. (I rent my next door neighbor's for $50 a month!) Yep, I think we Nothern NJ fellas need to get together. Do guys attend the NNJ PCA meetings? I haven't gone to one yet.

Gavin

[Grady Clay]

Ron,

Sounds like it is too rich. What is your overall gas mileage? Have you measured the CO?


The next area I would look at is the MFI injection nozzles. They are supposed to hold pressure and not dribble. The opening pressure is 213-256 psi. If they don’t seal when parked and the pressure is lost in the pipe, then the hot head boils the fuel in the nozzle and pipe close to the cylinder head. This dumps the fuel into the intake runners and can fill the air filter assembly with fuel vapor. This makes for a very rich condition while the engine is trying to start after heat soak. The MFI pump has hot (180-210F) engine oil directly under and next to the fuel circuit. Once the engine is shut off there isn’t any cooling fuel circulation. This is another place where the fuel can boil and get past a leaking injection nozzle.

The fuel tank is a cooling “thermal reservoir” for the MFI pump. If the level is low in the tank, the fuel will heat up and possibly overwhelm the fuel vapor recovery system. This is particularly true when the engine isn’t running and the charcoal canister is old. This puts fuel vapor into the air filter assembly.


While the engine is trying to start it is having to refill the pipes and nozzles with liquid fuel. This can cause it to suddenly go to too lean condition. This can be particularly dangerous because the engine tends to backfire through the intakes and can ignite fuel vapor or condensed fuel.

This hot soak condition goes away after the engine has cooled sufficiently. The fuel vapors in the air filter assembly have dissipated to the atmosphere. The cold start circuit overwhelms the lean condition from refilling the pipes and nozzles. You should always turn the electric pump to “on” for a couple of seconds prior to cranking. You can hear the fuel vapor bubble being returned to the fuel tank from the MFI pump.


Yes, there are some “failure modes” where the cold start operates when it shouldn’t.

Before getting carried away replacing or adjusting anything, you should do some careful diagnosis (the Check & Measure part of CMA.)

Best,
Grady

[bkreigsr]

Whoa, that's a new one on me.

I knew there was a reason I didn't chuck that whole charcoal canister recirculation system 20 years ago to save .7 lbs.

What is the proper interval for the charcoal canister replacement?
based, engine hours, miles driven, or calender?

How can I tell if it is too full to function?

thanks Grady

[john walker's workshop]

keeping the throttle open while cranking cures many hot start issues, both MFI and carbs. don't pump it. one long continuous crank over until it starts, not short periods of cranking, stopping and cranking again.

[Gasman59]

Grady, Thanks for the deatiled information.

Can't be too rich. Just passed emissions.

Also, If I pres my "Enrichment" button (Manually activates the enrichment solenoid) when this is happening, she fires right off and runs well.

I will check the items you indicated.

I will admit that I have jumped to the wrong conclusions too many times causing much unecessary work. Your advice, C&M is worth a thousand $$.

Thanks, Ron

[Grady Clay]

Here is a related thread:
Hot Start With Carbs


Good question about the longevity of the evaporative emissions container. I don’t recall ever seeing that listed. A year or two ago someone posted where theirs failed and filled the air cleaner with little triangular shaped pellets.

A good test would be to disconnect the vapor hose from the back of the air cleaner and vent it outside the engine compartment. See if the problem persists or disappears with low fuel and hot weather..

Which solenoid does your cold start button operate? The one on top of the fuel filter consol or does your MFI pump have two solenoids? If you activate the cold start and the warm start problem goes away, I would suspect the MFI nozzles. Take your MFI nozzles to someone with a Bosch nozzle tester.

Best,
Grady

[blucille]

there is some chat around here about a drive up the palisades this weekend...I can attend, but am flying out sunday night.

I'd be happy to host a gathering later in fall, once I get some leaves cleaned up....

-Lewis

[Gasman59]

Hi Grady: I guess that will be the next step. Rats!
Would the car run great if there were injector issues or is it just a slight leak that bleeds out over time.
Are the injectors rebuildable? They seem quite expensive to replace.
Thanks again for the advice.
Ron Young

70 Porsche 911E targa
73 Jaguar XKE Series III V12 OTS