3.2 hot start problem

Magnus911 · 07-09-2011, 05:35 PM

Okay so I finally got my trusted Bentley book out to try and figure out what's going on with my newly purchased '84 Carrera. You know the routine...starts fine when stone cold but once warmed up it cranks over and over but fails to start. I ordered a fuel pump check valve, then if that doesn't work will change the pressure regulator. Now, I have just today figured out that I can start it if I floor the throttle when I crank the car over, my question of the day is can I damage anything doing so? I've always thought you can't give gas to a fuel injected car while cranking but it does the trick on my 3.2, and it is not flooding the car so am I okay to do this? The Bentley manual tells me the fuel pump only comes on when the engine actually cranks over, which is why I tried to give it gas while doing the cranking and it started fine. This will be my routine until I change that check valve and put in a clean fuel filter, hope this will cure the problem. Oh yes I also ordered a spare DME relay....(before someone tells me that is the problem)

DRACO A5OG · DRACO A5OG's Garage

Oh no, not the DME Relay but more likely the CHTS ( #3 Cylinder Head Temperature Sensor ). Is yours a single wire or the updated dual wire sensor? Take peak in the engine bay behind heater hose

You will not flood your car no matter how hard you try , it is controlled by the DME :-). I tried.

Well, you need a back relay anyways

Magnus911 · 07-09-2011, 07:17 PM

Yeah I also thought about the #3 CHT sensor which would make very good sense. I want to check it with an ohm meter tomorrow per the Bentley manual, but am a bit confused as to how exactly the temperature readings are taken and where they are taken. I can see where to take the ohm readings but not sure where to get my temp readings; can anyone share their experience doing this? Many many many thanks in advance.

BGCarrera32 · 07-09-2011, 07:28 PM

I will direct you to the portion of the Bentley manual on how to check residual fuel pressure...

I had exactly the same hot restart issue for a while as well and it was a failing fuel pressure regulator at the back of the driver's side fuel rail.

kidrock · 07-09-2011, 11:58 PM

Quote:

Originally Posted by Magnus911

Yeah I also thought about the #3 CHT sensor which would make very good sense. I want to check it with an ohm meter tomorrow per the Bentley manual, but am a bit confused as to how exactly the temperature readings are taken and where they are taken. I can see where to take the ohm readings but not sure where to get my temp readings; can anyone share their experience doing this? Many many many thanks in advance.

Ummmm, if I remember correctly, the temperature readings you are talking about will be the ambient temperature (meaning, the temperature of the weather you are experiencing). Or if the temp in your garage is 70 degrees, 80 or 90 whatever. The ambient exterior temperature will affect the resistance of the sensor. I've always tested the CHT while the motor was cold.

Flat Six · Flat Six's Garage

Quote:

Originally Posted by kidrock

Ummmm, if I remember correctly, the temperature readings you are talking about will be the ambient temperature (meaning, the temperature of the weather you are experiencing). Or if the temp in your garage is 70 degrees, 80 or 90 whatever. The ambient exterior temperature will affect the resistance of the sensor. I've always tested the CHT while the motor was cold.

Not ambient temp, check temp of #3 cylincer head (well, any cylinder head; absent some major issues alll should be about the same -- for CHTS testing purposes, anyway). For $25 or so you can get one of those non-contact thermometers with a laser pointer.

kidrock · 07-10-2011, 02:12 PM

Quote:

Originally Posted by Flat Six

Not ambient temp, check temp of #3 cylincer head (well, any cylinder head; absent some major issues alll should be about the same -- for CHTS testing purposes, anyway). For $25 or so you can get one of those non-contact thermometers with a laser pointer.

so wouldn't it be possible that if the ambient temp is around 70 degrees, wouldn't a cold motor also be within the same temp, plus or minus a few degrees?

Magnus911 · 07-24-2011, 07:33 PM

Okay so I finally got around to jacking up the car over the weekend and replaced the check-valve on the fuel pump. Took the car out this evening for first test drive, got it nice and hot and drove it for 30 minutes or so, came back home and parked it. Went back out to start it an hour later and she fired right up, no hesitation whatsoever. Just to be sure, I'll do this again tomorrow and see what happens. I still have not checked the CHT sensor as I was waiting to do the check valve first, seems all is well for now. Will post again if problem persists, just to annoy everyone....

DRACO A5OG · DRACO A5OG's Garage

Outstanding!

Flat Six · Flat Six's Garage

Quote:

Originally Posted by kidrock

so wouldn't it be possible that if the ambient temp is around 70 degrees, wouldn't a cold motor also be within the same temp, plus or minus a few degrees?

Yes, but you'd want to check the CHT with the engine warm, too, to make sure resistance is within spec. CHT resistance varies w/temperature; just because it reads close to spec at one temp doesn't mean it provides proper signal to DME at all temps.