weird starting issue...

[painterdave72]

so i havent used my car for a week.. it would not start for a few tries but it finally did.. it just chugged for a few seconds and died like 2 times before it ran.. the car runs excellently... it is a complete restoration by me.. most everything on the car is new or refurbished.. the engine i have rebuilt with dpi cams.. and all new fuel parts. .new timing chains.. connecting rod bearings .. oil pump. rockers all cleaned and refurbished... etc etc...so any thoughts on why it did this would be great.... i went out about an hour after i had it running for a few mins and it fired right up first click... just didnt want to start after sitting for a week for some reason... its about 100 degress out.. so im assuming the cold start valve wouldnt work and i checked and it was not spraying.... also checked the 2 wires on the thermotime switch and they both have voltage at crank.. unless i unnplug the cold start valve then only one wire had voltage at crank.. is that right??? my accumulator is only abou t a year old as is my original style fuel pump and i run with no 02 sensor hooked u p since i have dpi cams.. etc etc.. any thoughts?? thanks..Dave..

[Helirich]

It sounds like fuel. The accumulator won't help a week later. When you went to start it, did you turn the key on for a few seconds before cranking?

[Bitsyncmaster]

so i havent used my car for a week.. it would not start for a few tries but it finally did.. it just chugged for a few seconds and died like 2 times before it ran.. the car runs excellently... it is a complete restoration by me.. most everything on the car is new or refurbished.. the engine i have rebuilt with dpi cams.. and all new fuel parts. .new timing chains.. connecting rod bearings .. oil pump. rockers all cleaned and refurbished... etc etc...so any thoughts on why it did this would be great.... i went out about an hour after i had it running for a few mins and it fired right up first click... just didnt want to start after sitting for a week for some reason... its about 100 degress out.. so im assuming the cold start valve wouldnt work and i checked and it was not spraying.... also checked the 2 wires on the thermotime switch and they both have voltage at crank.. unless i unnplug the cold start valve then only one wire had voltage at crank.. is that right??? my accumulator is only abou t a year old as is my original style fuel pump and i run with no 02 sensor hooked u p since i have dpi cams.. etc etc.. any thoughts?? thanks..Dave..

The cold start valve will not work if the engine temp is above (think it's 95 deg/F). So yes after sitting for a week or two my car requires the CSV to get it started. So if your air temp is above that 95 deg then the CSV will not fire.

[painterdave72]

my fuel pump primes itself with the key on.. so not sure.. and another friend looked in the bosch handbook and it says the cold start valve is supposed to fire no matter what temp just for longer or shorter periods.. .....

[Ron]

and another friend looked in the bosch handbook and it says the cold start valve is supposed to fire no matter what temp just for longer or shorter periods.. .....Na, Bitsy is right -- The bi-metal arm inside the TTS bends and quits grounding the CSV at 35C (95F). But the arm's heater will keep heating regardless of the temp (anytime the key is in the start position). Check out D:01:10

If it does it again, the 1st time it dies try pushing the air plate down and releasing it as quick as you can. If it needs fuel, that will give it some and help get it going. Otherwise, it will then probably take several more than two tries to get it going (flooded).

Fwiw, a lot of Ds prime when the key is first turned on. Others may or may not (depending on distributor rotor position...me thinks).
1669 usually did, But I just bumped the key and turned it off if I didn't hear the pump prime. Worked every time for me.

[82DMC12]

So what I am hearing here is that the DeLorean fuel system naturally has a tough time starting "cold" when the ambient temp is over 95F and there is no / very little rest pressure. Is this because the thermotime switch assumes it is hot (not grounded) due to ambient coolant temp which would also assume there is rest pressure held by the accumulator? If so it seems like a small flaw in the Bosch K-Jet design. Maybe it doesn't reach 35C in Germany often :-)

I have a Bosch fuel injection book (not written by Bosch) that says under pulsed injection design (not continuous design) that the cold start will always fire but for a diminishing period of time the higher the temp sensed by the thermotime switch. In the sections on continuous injection it doesn't say the thermotime switch is "off" at 95F but of course that is what our DeLorean manual says and can be easily proven with a multimeter.

Dave's issue, to me, is the thermotime switch is not grounded due to high AIR ambient temp and a lack of rest pressure since the car sat for a week. How do those of you in Arizona and Las Vegas, etc deal with this? I have Dave M's RPM relay which always primes the pump and I think that would solve the problem.

[Bitsyncmaster]

So what I am hearing here is that the DeLorean fuel system naturally has a tough time starting "cold" when the ambient temp is over 95F and there is no / very little rest pressure. Is this because the thermotime switch assumes it is hot (not grounded) due to ambient coolant temp which would also assume there is rest pressure held by the accumulator? If so it seems like a small flaw in the Bosch K-Jet design. Maybe it doesn't reach 35C in Germany often :-)

I have a Bosch fuel injection book (not written by Bosch) that says under pulsed injection design (not continuous design) that the cold start will always fire but for a diminishing period of time the higher the temp sensed by the thermotime switch. In the sections on continuous injection it doesn't say the thermotime switch is "off" at 95F but of course that is what our DeLorean manual says and can be easily proven with a multimeter.

Dave's issue, to me, is the thermotime switch is not grounded due to high AIR ambient temp and a lack of rest pressure since the car sat for a week. How do those of you in Arizona and Las Vegas, etc deal with this? I have Dave M's RPM relay which always primes the pump and I think that would solve the problem.

I think the injector lines get some air pockets when sitting for a week or more. Priming the accumulator does not make any fuel flow in the injector lines. My hot start relay will fire the CSV after one second of cranking no matter what temp the coolant is at.

[David T]

When a car sits for a long time you lose all rest pressure. On start-up it takes a moment for the fuel pump to create enough pressure to operate the CSV. The CSV doesn't require much, not like the injectors, but even so it still needs some pressure. Once the motor gets started on that initial fuel from the CSV, the pressure is supposed to get built up enough to operate the injectors and keep the motor running. It may run roughly for a moment till the pressures balance and the motor runs smoother but till it warms up it is not running smooth. The better it is tuned up and everything is working the smoother it can run. A lot depends on the ambient temperature too. The colder it is, the better it tends to run as it warms up. If you are having problems during warm-up go over all of the warm-up systems and make sure you don't have any vacuum leaks. Vacuum leaks reduce the ability of all of the systems to operate properly. As rubber parts age, they tend to leak or leak more making the motor run badly. Check the injector seals, if they are hard they are leaking.

[Ron]

+1


So what I am hearing here is that the DeLorean fuel system naturally has a tough time starting "cold" when the ambient temp is over 95F and there is no / very little rest pressure. Is this because the thermotime switch assumes it is hot (not grounded) due to ambient coolant temp which would also assume there is rest pressure held by the accumulator? If so it seems like a small flaw in the Bosch K-Jet design. Maybe it doesn't reach 35C in Germany often :-)

I have a Bosch fuel injection book (not written by Bosch) that says under pulsed injection design (not continuous design) that the cold start will always fire but for a diminishing period of time the higher the temp sensed by the thermotime switch. In the sections on continuous injection it doesn't say the thermotime switch is "off" at 95F but of course that is what our DeLorean manual says and can be easily proven with a multimeter.

Dave's issue, to me, is the thermotime switch is not grounded due to high AIR ambient temp and a lack of rest pressure since the car sat for a week. How do those of you in Arizona and Las Vegas, etc deal with this? I have Dave M's RPM relay which always primes the pump and I think that would solve the problem.
No -- It doesn't need rest pressure when the engine is cold... Rest pressure is for keeping the fuel in a liquid state when the ENGINE is hot. (Basically, gas bubbles screw up the delivery system (and pump operation on other vehicles).
The TTS doesn't look at ambient temp. It's in a coolant passage and takes on engine temp... Think of it and the CSV as a substitute for a choke, but rather than reducing the air, they increase the fuel. If everything is up to par, they're not needed when the ENGINE is 95F.

A multimeter will convince you :smile: ...look at the diagram in the manual to see how it physically works.

[Bitsyncmaster]

If everything is up to par, they're not needed when the ENGINE is 95F.

But if your injector lines are not primed full of fuel and your ambient air temp is 100 deg then your coolant temp is also 100 deg. Then you do need the CSV unless you crank fast enough to pull on the air plate.

[David T]

Rest pressure serves two purposes. The first one is to prevent vapor lock by keeping the fuel under pressure to prevent it from boiling till the motor cools off. The other purpose is to provide enough pressure to operate the injectors because the CSV will not operate if the engine is hot so the injectors must start working right away and it takes time to get the pressure up high enough and longer if you aren't starting at "Rest Pressure". When the motor is shut off it eventually reaches ambient temperature. If it is summertime and the car is out in the hot sun, you might never run the CSV to restart the car. Deloreans originally came with a sticker on the sun visor that said to give the car 1/4 gas pedal to start. Most, if they are running well, do not need any pedal to start but some benefit from it. Another thing you can do is cycle the ignition switch on and off several times to get the fuel pump to run before trying to start the motor. Or try Dave's relay.

[painterdave72]

It only did it that one day it was really hot in the garage.. it has cooled off a bit since then and fires right up no issues first time... took it to a large car cruise today and ran great... so just a weird anomaly.....lol

[Ron]

But if your injector lines are not primed full of fuel and your ambient air temp is 100 deg then your coolant temp is also 100 deg.
When the engine is 'cold', yeah. The injector lines should always be full (but not always pressured up, which is what I think you meant...).


Then you do need the CSV unless you crank fast enough to pull on the air plate.It cranks fast enough to pull the plate down hot or cold. (Guessing 8-9 CFM going through with stock cams.... The DPI cams might have lower vacuum while cranking, but not that much.) You can pull the coil wire and watch the plate wiggle up and down. Remember, when roughing the CO in, how little you have to turn the CO screw backwards to make them stop spraying. Or how a slight push during warm up at idle will kill it.)

I'd lean towards it being the tune, not priming every time the key is turned on, possibly in conjunction with the cams, or, something odd like a vacuum leak that shows up when dead cold (if it persists) or a hiccup, especially with the problem showing up at 100F ambient.

FWIW, if it was after an hour or so, only, I suspect leaky injectors flooding it. Not a "hot start problem".