2.7L MFI start problems - warm engine

[stylomylo]

i'm still having problems starting my 2.7L MFI engine when it's warm.

cold start - fires right up
hot start (within 10mins of switching off) - easy peasy, fires right up
warm start (30mins-3hrs after switching off) - starts are random, & when it doesn't fire, i can crank for 5mins and engine will not fire.

my car has flwg fitted :

1) brand new MSD box & MSD coil - engine runs great, idles very smooth, power delivery also very smooth and engine pulls like a train between 3-6.5k rpm
2) manual fuel prime switch to aid cold start
3) does not have a fuel accumulator
4) new distributor rotor and and cap
5) new spark plugs

what else have i missed out? what could be causing my warm starting problems

pls help

[GrantG]

Let the fuel pump run for a few seconds before hitting the starter (key turned to ON but not start).

Did you try it with the gas pedal to the floor? A squirt from the manual prime might help too.

If those things don't help, you probably need to adjust the idle mixture control (probably needs to be richer - push and turn clockwise)

[Grady Clay]

I agree with Grant, heat soak of the CDI may be an issue.

Grant’s admonition to turn on the electric pump for a bit is right on the mark. Fuel can boil in the MFI pump at the piston inlets. This gasoline vapor bubble can be taken into the high-pressure piston and into the steel pipes to the nozzles. This compressible vapor prevents the nozzle from opening. You have to wait for the system to cool and the bubble be absorbed.

Turning on the electric pump purges the vapor bubble and circulates cool fuel through the MFI pump. This is proper starting procedure every time you start an MFI engine – hot or cold.

Another possibility is the fuel injection nozzles are not holding pressure. I would pull them and have them checked. They might benefit from ultrasonic cleaning. There are also check valves in the fuel outlet ports on top of the MFI pump. They too can be cleaned.

What MFI pump do you have? If you have the ’69 front cover with the cold enrichment solenoid (two solenoids: cold start and over-run shut-off), you can manually use that to purge the high-pressure system while cranking.

Best,
Grady

[Rusty 356]

Question: Does the MFI system have a residual pressure valve in the system?
If so could you put a pressure gage on the fuel filter and watch fuel pressure as the system cooled?

[stylomylo]

Originally Posted by Grady Clay

Another possibility is the fuel injection nozzles are not holding pressure. I would pull them and have them checked. They might benefit from ultrasonic cleaning. There are also check valves in the fuel outlet ports on top of the MFI pump. They too can be cleaned.

What MFI pump do you have? If you have the ’69 front cover with the cold enrichment solenoid (two solenoids: cold start and over-run shut-off), you can manually use that to purge the high-pressure system while cranking.

Best,
Grady

Thanks for all your responses. Keeping the fuel pump running first seems to work (for now..... fingers crossed)

I'm not sure what MFI pump i have but my car is a stock 1974 2.7L MFI & the MFI has never been replaced, only rebuilt.

Maybe stupid observation (pls bear with me. I'm technically incompetent) but I also noticed that some of my injectors, looking at them from the engine bay are rusty. is this normal? Could this be one of the reasons why they are not holding pressure?

[Grady Clay]

Originally Posted by stylomylo

Keeping the fuel pump running first seems to work (for now..... fingers crossed)

...some of my injectors, looking at them from the engine bay are rusty. is this normal? Could this be one of the reasons why they are not holding pressure?

Good. That issue may just have been a starting technique.

Rust on the outside of the nozzles doesn't effect their performance. If everything works correctly, leave it alone. Now is the time to do a complete Check & Measure part of CMA and get yourself a good baseline for your engine.

Is your engine the 210 hp type 911/83?

Search this Forum on MFI. Start yourself notebooks (electronic and paper). You want to become the best educated possible about your engine and MFI. Qualified techs are increasingly hard to find. You are best to diagnose anyrhing.

Best,
Grady

[stylomylo]

Originally Posted by Grady Clay

Is your engine the 210 hp type 911/83?

Yes, it's a 911/83 original 1974 911S engine, european spec. i believe it's the same engine as a 1973 2.7L 911RS engine.