1990 760 hard starting cold

crg · Post by **crg** » 23 Nov 2006, 10:00

I'm on my second 1990 760. The 1st was great 200K. Purchased a new one 70K. This car has always started hard. It gets much worse in the colder weather.

Car is tuned and runs well when warm. Needs 20-40 seconds of cranking to start and runs rough for a few minutes. Car will start just fine for the rest of the day, up until it has sat for 5-6 hours. Just turning the key numerous times to activate the fuel pump doesn't work but may help. Pressure seems fine. Pressure regulator was changed, no help. Injectors were changed and cold start injector seems fine.

Acts as if it is a fuel issue, but all seems well. Have changed ECU's between the 2 cars. Nothing helps.

My mechanic, a good volvo guy is stumped. Possible wiring issues? Grounds?

Any other ideas?

Help!

Kmaniac in California USA · Post by **Kmaniac in California USA** » 23 Nov 2006, 21:59

Have you checked the operation of the in-tank fuel pump? Check the fuse, which is separate. These cars will run with the main fuel pump only so this can be deceiving. If the in-tank pump fuse is blown, change this pump and the attached filter sock immediately. If you go to the trouble of removing the in-tank pump from the car, you may as well replace it while you have the chance. NEVER replace the main fuel pump without changing the in-tank pump at the same time!!! Start here and let us know what you find.

crg · Post by **crg** » 26 Nov 2006, 07:52

Yes the in-tank pump works. At least by sound and the pressure at the rail comes right up when the key is turned on.

ToeCutter66 · Post by **ToeCutter66** » 26 Nov 2006, 15:41

If you get good fuel pressure when you turn the key, it might be time to check the compression on the motor.

crg · Post by **crg** » 27 Nov 2006, 05:39

Compression checks out fine. Engine runs Fine when warmed up.

One other oddity that leads me to believe there is some possible electrical issue is the bank of three relays under the hood. When I change these out with the ones from my other 1990 the car will not shut off. Also at sometime someone ran a jumper wire to the coil from a hot lead off of the ECU. Connected or unconnected the starting and not turning off remains the same.

Basically I've swapped and re-swapped ECU Main Controller and all relays from my other car to no avail. I've always replaced the original items as not to complicate the issues.

Help
Help
Help

Has anyone replaced a complete wiring harness? Should I spend the $$ or rip apart every inch of the old one?

ToeCutter66 · Post by **ToeCutter66** » 27 Nov 2006, 09:58

Try this:

http://www.swedishbricks.net/700900FAQ/ ... heck_Valve

crg · Post by **crg** » 01 Dec 2006, 14:16

My mechanic and I have verified that we are not seeing any abnormal drop in pressure overnight.

It looks as if I'm going to have to pull the car and either work on it myself or junk it!

One item that keeps popping up is the temp sensor. It does throw the alarm on occasion and is presently in the on state. The sensor has been replaced and I'm told the wiring is good???? I suspect a slight voltage "leak" could be occuring in the wiring that leads the ECU to believe it's very hot and therefore isn't dumping enough gas. Car starts and runs fine when hot, or if its hot outside. No 90 degree days now.

I will attempt to check myself this weekend. 3Volts at 32F or 6k ohms.

Once the car is running does the oxygen sensor override the temp sensor? Or does the temp sensor continue to have input to the ECU?