joel91

My 91n/a runs fine its just when i start the car hot after sitting for ten minutes
it idles rough for about 30 sec then its fine?? Could it be something to with the fuel pressure solenoid....i know from the fsm the fpr shouldn't get vacuum until 50 sec after a hot restart. I'll check this today and post later. Any other suggestions???

HAILERS

Yes! FPR solenoid. Count the seconds next time.

I think on cars fitted with Fuel Pump Relay/Resistor packages there is a relationship. I'm sorta working on that idea right now. I'm thinking when the engine is hot the relay feeds a full 12v and after you get going it returns to the 9-10vdc feed. I can hear this relay click because I've one in the back of my car in the jack area and I can hear that relay clicking on hot starts and then moving/driving off in the car.

Most Fuel Pump Relay/Resistors are located up front near the afm/filter, so you won't be able to hear it.

Your right though about the fpr solenoid cutting vacuum to the fpr for 50 seconds causing the fpr to regulate to approx 39psi, then after 50seconds putting vacuum back on the fpr and the fpr regulates to 28-30 psi depending on the condition of the engine.

joel91

great i'm going to check this tonight....oh and by the way i hear clicking too on a hot restart it sounds like it coming from the right front corner of the car....is that the fuel pump relay resistor?? Could that be the cause of my problem too???

YearsOfDecay

Whats happening is that the fuel is boiling in the primary rail (second too probably) and when you start the car, the fuel delivery is messed up until the rail gets cooled by new fuel entering the system from the tank.

By not letting the FPR get vac for a while after restart when hot.. the fuel pressure is higher in the rail, and thus more fuel gets put in to compensate for the heat in the rail.

you can compat this by cycling the fuel pump a few times before you start the car.. (but if you got a leaky injector... it'll puke out)

I had that clicking too before the haltech retro fit..... never bothered to figure out what it was

HAILERS

I can't believe people can hear that relay up front. Gotta get me a hearing aid.

joel91

i just had the injectors professionally cleaned.....and i checked the vacuum to the fpr on a hot start and i counted 53 sec( my counting must be alittle fast=) until i have vacuum at the fpr. So Years of Decay fuel boiling i guess could be happening. I'll try cycling the key tomorrow a couple of times and see if that helps......thanks

joel91

and yes it is a very faint click noise, yea you really gotta listen closely to hear it....but voltage to the pump really shouldn't matter right??? that is what the fpr is for right???

HAILERS

I don't understand *Cycling the key*. Unless you mean to START, then letting off immediatley and doing that several times. The pump does not run when you just go to ON. But you knew that.

joel91

i may be mistaken but i thought on an Series 5 turning the key to On turned the fuel pump on, and series 4 only cranking the engine made the fuel pump run??? Anyways, what are the conditions for vacuum at the fpr??? like temperature wise...
the reason why i am asking is i got the engine up to operating temps and went for a drive last night. Parked the car and went out about 45 min later and it started to run rough as soon as it started.
the temp gauge on the dash read about 1\4 and i ran out in front and checked and there was vacuum to the fpr and that was within 15 of the restart.... So the question is what are the conditions for vacuum to the fpr.

HAILERS

Nope. Series five is the same as series four. Key has to be to ON and the engine running or the key Held to Start.

Turning the key to ON without the engine running results in no fuel pump action (unless the fuel pump check connector is coupled). After market ECU's a different thing though.

HAILERS

As for what HOT means: If you look at your series four FSM, page 4A-80, you'll see that when they checkout the FPR solenoid, they jumper the Intake Air Temp Sensor with a 2-3K ohm resistor to simulate HOT.

Now if you look at the next page over, page 4A-81, there is a chart there. It shows that at 122*F the resistance of that sensor is 11.85K ohms plus/minus 1.19K ohms. And at 185* the resistance of that sensor is 3.5K ohms plus/minus 0.35 ohms. So I assume from those figures, HOT is when the Intake Air Temp Sensor is somewhere around 190-200 degrees and above.

If its hot on a series four, the book says no vacuum will go to the FPR for 50-90 seconds.

The series five book, when talking about the Fuel Pump Resistor and Relay, in the OutPut Devices page, says it'll put out a full 12vdc during HOT conditions at idle. That explains the clicking from the Fuel PUmp Resistor Relay package sometimes.

And the series five fsm says/mentions the reason for no vacuum to the FPR during HOT conditions (for 50-90 seconds), is to prevent Percolation of the fuel in the rails.