Rest pressure

[Josh]

As i am driving my car more and getting it running better and better I have time to consider the smaller issues. One of these things is the hard starting.

It takes at least half a dozen cranks to start the car; more than unusual. I noticed today when programming my keyless entry (had to turn on and off the ignition, so the fuel pump was cycling) that the car fired right up after 1 crank. So this tells me the fuel system is not holding pressure. I notice after going out for supper or something (hour or so of the car sitting) it starts up faster but still requires a decent amount of cranking. it has nothing to do with cold/hot starts as far as i can tell, if i cycled the ignition a few times in the morning before i started the car it would fire right away.

Also things to consider: I am efi, not kjet. I am still running an accumulator.

Where would i go about troubleshooting this issue?

Thanks, Josh

[BABIS]

fuel pump check valve?

[Josh]

I have one installed. Came with my fuel pump (DMC integrated sender/pump unit)

[DMCMW Dave]

I have one installed. Came with my fuel pump (DMC integrated sender/pump unit)

Rest pressure shouldn't be a big deal with EFI as your electronics is opening the injectors. It's a K-jet problem as compressed air won't open the injectors. Modern EFI cars don't have accumulators at all.

Is there any way that you could have a leaky injector or two, i.e. such that they'd bleed out when off? That would drain the fuel rail and then take a second or two to fill it back up, but it would also seem to cause a flooding issue.

[Josh]

Rest pressure shouldn't be a big deal with EFI as your electronics is opening the injectors. It's a K-jet problem as compressed air won't open the injectors. Modern EFI cars don't have accumulators at all.

Is there any way that you could have a leaky injector or two, i.e. such that they'd bleed out when off? That would drain the fuel rail and then take a second or two to fill it back up, but it would also seem to cause a flooding issue.

Yeah if i had known better when I was putting things back together i would have omitted the accumulator and modified the hard lines accordingly. Oh well, its doing no harm.

THat is a good suggestion. Ill check out the injectors. I did test them for leaks during install by installing them into the fuel rail, but not the manifold. set them all in spray paint caps and cycled the ignition a dozen times. Some of the cups were a little moist at the bottom, that small leakage may be the issue. i am just running some take off injectors out of a mustang given to me from a friend to get away from the rusty low impedance eagle ones.

[David T]

Yeah if i had known better when I was putting things back together i would have omitted the accumulator and modified the hard lines accordingly. Oh well, its doing no harm.

THat is a good suggestion. Ill check out the injectors. I did test them for leaks during install by installing them into the fuel rail, but not the manifold. set them all in spray paint caps and cycled the ignition a dozen times. Some of the cups were a little moist at the bottom, that small leakage may be the issue. i am just running some take off injectors out of a mustang given to me from a friend to get away from the rusty low impedance eagle ones.

How is your EFI system handling cold starting? Is it enriching the mixture in any way? Is there an equivalent for the cold start valve? When cranking are you getting full voltage to the ECU and the ignition system or is the starter dropping the voltage too much? How your EFI is wired up is very important. On some cars there is a built-in delay before the starter will crank to allow the fuel pressure to build up. Most EFI systems run at lower pressures that the K-Jet does. You may not have a leaky injector, you may have fuel leaks in your modified plumbing. One of the main reasons for "Rest Pressure" is to keep the fuel from vaporizing because the motor is hot. Once the fuel vaporizes you can't pump it or inject it. Sounds like you have 2 problems, hard cold start and hard hot start. They are probably inter-related meaning if you fix one you will improve or fix the other.

[DMCMW Dave]

...... Once the fuel vaporizes you can't pump it or inject it. .

Yes you can with EFI. The gas in the tank (where the pump is) does not vaporize. The injectors will open just fine full of air (unlike KJet).

[Josh]

Yes, there is an equivant of a cold start value, its called warm up enrichment. When the coolant temp is below operating temp it refers to a graph that richens the fuel air mix accordingly.

the pump primes when i turn on the ignition and is computer controlled from there on as the computer sees fit.

Yes it is a hot start and cold start problem definitely, but as it is both it just makes it a plain old starting problem haha. My fuel system is not modified, well as far as the lines running along the frame and to the tank are concerned.

but it is definitely worth looking into the rest of the system for leaks. perhaps ill remove the feed and return lines (before the fuel rail and regulator) and rig up a jig to pressure test off there. im going to swap out the injectors and go from there though, see if that makes a difference as it is an easy swap.

[opethmike]

Warm up enrichment is for AFTER the engine starts, it doesn't aide in cranking at all. The priming pulse and cranking pulse tables are the only ones that get used during cranking.

This is going to be a weird question, but does it fire more quickly if you crack the throttle during cranking? I ask because I had a similar issue with my MS install, and it turned out to be that my cranking idle control air valve values were not large enough.

Barring any hardware or mechanical issues, the three software places to check are the priming pulse table, the cranking pulse table, and the cranking IAC values table.

[Josh]

Warm up enrichment is for AFTER the engine starts, it doesn't aide in cranking at all. The priming pulse and cranking pulse tables are the only ones that get used during cranking.

This is going to be a weird question, but does it fire more quickly if you crack the throttle during cranking? I ask because I had a similar issue with my MS install, and it turned out to be that my cranking idle control air valve values were not large enough.

Barring any hardware or mechanical issues, the three software places to check are the priming pulse table, the cranking pulse table, and the cranking IAC values table.

I have tinkered with the priming and cranking pulse tables. Not the cranking IAC values though. They did not change anything, In fact increasing the priming pulse caused issues with hot starting.
I tried giving it gas when cranking (<70% tp as that is what the flood cancel is set to) and it made no difference.

Ill try giving it more air during cranking, thanks for the tip Mike. Ill report back.