1987 740t over rich and misfiring

TAJavelin · Post by **TAJavelin** » 04 Jan 2011, 06:32

Things already done, in order
Replaced wiring harness with new one.
Replaced MAF with good used one.
Noid checked fuel injector wires they are firing and not a constant on.
Checked temperature sensor on block ohms at temperature right on.
Checked ecu voltage at temp sensor within parameters for the temp outside.
Cleaned injector grounds.
Sprayed carb clean over entire engine looking for vacuum leaks.
Replaced Fuel Pressure Regulator

Ok To start off this car had a bad harness that was totally disintegrated and that was the start of all these problems. I cleaned the plugs up (so coated in soot it would not start) after the last try which was fuel pressure regulator. It runs but running rich it seems to be sporadic. Meaning it has a kind of lumpy idle, not chugging. like a small miss. If I step on the gas it will accelerate rough belch black smoke and then accelerate properly. When it is cold it will pop into the airbox. I plan on picking up injectors tomorrow as well as anything else I can get my hands on. At the moment I am borrowing parts from my 940 which runs great and swapping them to the 740.
I do have a smell of gas in my 150mi oil change and that will be addressed again as I don't feel like wasting yet another oil change. Oil level is at norm but just giving all the info I can. I am at a dead loss and stumped. Is it possible that a bad O2 can make it run this poorly ? Can it have 4 bad injectors ? Is the ECU bad ?

Thanks
Bob

Post by **billofdurham** » 04 Jan 2011, 12:20

Welcome to Matthew's Volvo Site.

Which temp sensor did you check? There are two. The front one is for the gauge and the rear one, under intake manifold runner #3 is for the ECU.

How long is it since the plug leads and rotor arm were checked/changed?

Other points to check:
Earth (ground) leads on the manifold.
Throttle valve loose or incorrectly adjusted.
Throttle switch incorrectly adjusted.
Throttle body dirty.

Bill.

TAJavelin · Post by **TAJavelin** » 04 Jan 2011, 16:49

Thanks for the quick response,
I did check the one under intake runner 3. Plug leads and rotor arms may be suspect. It has been about 2 years.
I am guessing by throttle valve you mean the black plastic adjustment in the 7-8 o'clock position on the throttle body, if so what is the correct way to calibrate ? I had taken it out and cleaned off the oil sludge then turned and cycled through the throttle and turned till it ran smoothly. I went to a salvage yard today and pulled off many pieces from a car that looked well maintained. The Mann oil filter and IPD rotors and new injectors were a good indication. As for adjustments for the throttle switch I will have to find the parameters. Tomorrow I will check all the above and do 1 by 1 replacements. I was lucky enough to score a ECU off a car with passed emissions, great looking plugs and a huge dent in the tail. Well worth the 30$ us. I will try all of the things you brought up first. And get back with a reply.
Thanks again
Bob

87 744t
91 945t
95 850t

Post by **billofdurham** » 05 Jan 2011, 11:29

Loosen the throttle position switch (TPS) adjustment screws holding it to the throttle body. First turn the TPS clockwise (away from the electrical connector) until it stops. While keeping your finger on the throttle disk so it won't move, turn the TPS counter-clockwise (toward the connector) until you hear or feel a click. Continue turning until it stops, then tighten the screws.

Bill.

TAJavelin · Post by **TAJavelin** » 09 Jan 2011, 16:10

Bill,
Thank you for all your responses, I am pretty sure I found the problem. A while back I had the head replaced and the wires for the hall sensor were dangling. While the car was running I wiggled the wires and the car died. I am pulling the distributor out tomorrow and see how bad the disi is. with the mileage I may just bite the bullet and replace the whole thing. if it seems good just seals and fix the clip I will reuse it and try again. Just wondering when the car was stalled and I wiggled the wires I heard multiple clicks throughout the engine bay. I could have sworn I heard injector click also. I am thinking the wires control much more than spark timing.
Thanks again
Bob

TAJavelin · Post by **TAJavelin** » 15 Jan 2011, 15:34

Update

I can honestly say for the first time in a long time I feel beaten. Went out of the norm and replaced the O2 sensor, changed oil, plugs and f.i. temperature sensor. The only things I haven't changed are the injectors and coil. Pulled the brand new plugs after 15min and they were black. with the engine temp warm and a turn of the throttle a puff of black out the exhaust. Besides the work I have done I will be back on it tomorrow and clean any and every ground I can find. But after that I am at a total loss on what the problem is.