1985 760Turbo Very Hard Starting/No Start

turbo no/go · Post by **turbo no/go** » 11 Jan 2008, 13:10

1985 760Turbo, Automatic, 185,000m.(2.3L 4cyl.- B230FT)
Car has been hard/impossible to start for about 3 weeks(engine turning/no start).When the problem started, it would take 2-4 tries to get it to start.That was unusual considering the car had started first try/every try for the 7 months prior (after both fuel pumps had been replaced).Gradually it became worse, taking 7-10 turns of the key to get it to go.Now I can spend 20mins trying to start it, which 90% of the time it finally does and then drives/sounds/seems completley normal.I can shut it off and it will always restart if I wait no longer than 10-15 mins.If I wait longer than that it goes right back to taking 15-20 turns of the key to start.
Shouldn't the fact that it restarts'immediately' after shut off but not if you wait 15-20mins tell me something obvious??
If I now rule out- coolant temp.sensor(new)
air mass meter(relatively new)
internal/external pumps and filters(new)
ballast resistor(replaced 10months ago)
fuel pump relay(new)
fuses(checked/cleaned replaced)
ground wires(checked/cleaned)
ignition control module(less than a year old)
fuel pressure regulator(1yr old)
battery(less than 2 years old and checked)
alternator(checked/working)
ignition coil(checked/working)
distributor/hall sensor(checked/cleaned)
plugs-wires(like new/cleaned/checked)
?????????????????????????????????
What exactly am I left with.
Starter?
Hopeless??
Thanks for any ideas.

Ragman · Post by **Ragman** » 11 Jan 2008, 17:03

This may sound like a redundant question but, when you replaced the fuel pump(main) did you also replace the check valve on the fuel filter? Seems insignificant however it holds the fuel at the pump so as not to run back from the pump and cause a pressure drop on startup. Also , the miss-firing at high rpm could be the thermostat in the air box that controls the air flow from the stove pipe to the intake.

turbo no/go · Post by **turbo no/go** » 11 Jan 2008, 19:41

Where exactly is the airbox thermostat?I looked inside my airbox today just to visually examine the filter and air mass meter, I don't remember seeing anything similiar to a thermostat inside.
Also where exactly is the check valve.I'm quite familiar w/ the filters and pumps having replaced them twice...is the check valve inside the 'top' of the filter?..inside the line between pump- filter?
Once I find the airbox therm. how do I check to see if it's faulty?Or can this be done?
Thanks for the advice.

Post by **sseir39** » 11 Jan 2008, 21:18

Best bet on these old jewels is to check brickboard.com then go to the RWD FAQ. This has the best trouble shooting guide there is.

Not sure about any check valve on this model. Have owned a turbo same year. It sounds as if you have been thorough, but check the above suggested.

Dick, also from TX

Ragman · Post by **Ragman** » 11 Jan 2008, 23:27

The check valve threads onto the the fuel filter and should be visible if you have replaced the fuel filter already. The thermostat is in the air box at the point of entry for the air to flow from the stove pipe. The thermostat looks like a brass bullet and when heated will keep the trap door from the stove pipe close to allow cold fresh air into the filter box. It usally fails in the closed position so that only hot air from the manifold flows into the air box. In warmer climates this hot air will cause a misfire at highway speeds almost like the engine misses a beat. IPD sells the thermostats and I'm pretty sure they supply a check valve with the purchase of a fuel filter, typically a Bosch filter.

turbo no/go · Post by **turbo no/go** » 14 Jan 2008, 16:12

OK the check valve was replaced about 7 months ago(when the new external filter/pump was replaced)so just based on age it should be fine,right?
As far as the airbox therm.,I removed the airbox cover again to examine it and when you press down on it(the 'bullet')the pipe 'cover' opens back and forth.It seemed to work by spring and was obviously metal so I sprayed a little WD-40 directly on the spring thinking perhaps w/age it was getting stuck??Waste of WD??
I've tried to start it w/the airmass meter unplugged,no start...no difference when plugged back in. I've cleaned what ground wires can be found, wires that connect to the block, the head and fuel rail/manifold just on the advice that this should be done. I've checked all fuses, the fuel pump relay is only 7 months old as well and 'clicks' every time.
????????
I'm really lost.It continues it's same routine without fail.I didn't use the car all weekend, just cleaning and checking what I can. But this morning it took about 8-10 tries to start, and after sitting for a few hours it got even harder.
The fact that it only restarts within 10 minutes of turning it off is saying something right?
Again, thanks for any advice.

turbo no/go · Post by **turbo no/go** » 14 Jan 2008, 19:10

I've been told also a leaky injector could be to blame, does this make sense and how do you test the injectors??

Post by **sseir39** » 14 Jan 2008, 19:14

Apparently you are hearing the buzzz when turning the key on just before you engage the starter. Means the FP is working and so is the relay. The car does start but becomes worse if you shut it off. Much later it will start reluctantly. Is this correct?

Did you do the tank pump and filter sock? Am just wondering because of some of the older Volvo's junk in the tank would block the filter to the point it would starve the fuel supply.

Did you check brickboard.com on their RWD FAQ? More ideas and help there. You have a tough one for sure.

Dick

Ragman · Post by **Ragman** » 14 Jan 2008, 19:28

Sorry to be a PITA but I was just re-reading your parts replacement list and wanted to know if the dist. cap AND rotor were replaced. The check valve was in fact on the main fuel pump, and the thermo stat in the air box won't be affected either way by the WD-40. If the car seems to start easier when warm, I was think about the coolant temp. sensor being faulty and when the engine is cold, the ECU isn't getting the signal for the cold start?? I'm a little bit removed from my 740 days however certain thing stick in my mind. The other thing I would get checked is the engine compression. You may have a low compression problem on 1 or more cylinders and this would certain cause a starting problem. A compression test should be relatively inexpensive. By the way, the air box thermostat reacts to heat and will move the shutter open or closed by expansion or contraction. You may see this happen with a blow dryer/ heat gun applied to the brass bullet.

turbo no/go · Post by **turbo no/go** » 14 Jan 2008, 19:40

Correct.
When you try to start it after sitting overnight it could take as much as 15-20 tries..I've spent 20 minutes or better just trying to get it to start, especially when it's parked in locations away from home and I have to get it moved.
Once it cranks, I'll let it warm a little and drive it 5-10 miles,turn it off and immediately try to start it and it restarts like there's no poblem, time after time and sounds and runs as normal. But wait 15mins...25mins. to try and restart it and here we go again!
Also, the intank pump/screen was replaced the same day as the main pump, which has been about 2 weeks ago now.
I keep going back to suspecting the fuel pressure regulator, am I missing something, other than the obvious knowledge?
Thanks.