Many thanks in advance for any help. I have a 1988 740 turbo previously owned by a Volvo dealer mechanic, well taken care of, 166k miles. A couple weeks ago coming home from work car bogged upon accelaration and continued. I did make it home with very little power. the next day it would start, run rough, and eventually die. long list of things I have checked:

checked vaccuum lines, replaced several. Replaced fuel pressure regulator, MAF sensor, plugs, wires, cap had a large crack in it- replaced cap and rotor. Remove flame trap- clean. Plenty of fuel from fuel rail. In tank fuel pump pushed out 1/2 cup or so of gas with just a pulse on cranking (line removed from back of main pump). Spark tester showd spark, Noid tester showed up good also for fuel injectors. The car was nearly empty when ititial symptoms appeared, have since added one gallon of gas. I also loosened exhaust from behind turbo- still no start. Also I had removed timing covers-timing looks good. Checked all fuses today with meter- switched out climate control fan 30amp and fuel selenoid...15amp. Fuel pump relay looks new inside- not sure how to test. Any idea where to go next? car has spark, fuel. Replaced air filter at last oil change. ???

Just today I

 

Changed the power transistor right in front on the left inner side (drivers side) of the car? Its just behind the headlight and this link here shows a 92-95 model transistor for 940 but you have a similar one in your 740 car.Volvo 940 Ignition Module - Free Shipping - Replacement, Standard, Bosch
If your pump is giving you gas then the fuelrelay is fine.

 

I had already switched out the ignition amplifier, knock sensor, and radio suppression relay. Sorry, left that out of the list. Just can't understand why this car wont run.

 

first thing to do is figure out if its spark, fuel, or mechanical. pull a spark plug, put it on a grounded surface (usually a bolt on the valve cover works), and crank the motor for a sec, do you see spark-spark-spark-spark ?

when you pulled that plug, was it wet or dry? what color is it?

pop the oil filler cap, crank over the car and verify the camshaft is turning, if not, its possibly a broken timing belt. if its turning, do a compression test in all 4 cylinders (and inspect the rest of the spark plugs while you're at it. if thats good, its probably not mechanical.

 

has spark and fuel. timing is good. I just realized I'm not sure if the fuel that I got out of the fuel rail is not just from in tank pump. gonna have someone crank while I listen and feel.

 

Pulled fuse eleven, had mother in law crank engine. Could feel and hear main pump working. Car should start. Cant think of what could be wrong.

 

When ive pulled plugs after cranking they are wet, i even replaced with new. Timing belt is intact- I even removed both covers and turned engine from crank. Timing marks line up. Dont know what I've overlooked? Idle air control valve cleaned. Done all I can think and read of.

 

I initially replaced the plugs and wires well before noticing the crackrd dizzy cap. think the plugs may have gotten foulded in the meantime. Pulled them and they were all soaked with gas. Two were quite blackened. Should I clean and dry or buy new, new plugs?

 

Yes,could be the spark plugs. Put new volvo original in.

 

Turbo was rebuilt a little over two years ago. I've had the car for six months. On first start up it would run rough, I would just give it gas quickly after putting it in gear, and then it would be fine. Untill now.

 

I think I will try new plugs again tomorrow.

 

Got new plugs, but did a compression test first.
cylinder #1 65lbs
cylinder 2 30lbs
cylinder 3 30lbs
cylinder 4 90 lbs

Does this sound like a good possibility that timing belt slipped. When I had it apart to check I could not locate timing mark on crank gear. Need help!

 

yeah, could well be. definitely WAY too low, I think these engines should be at LEAST 150psi per.

here's the markers...
Volvo B230 Timing Belt Alignment Marks

more timing belt tips here
Engine. Seals, Belts, Crankcase Ventilation

 

the car is running too rich--plugs are soaked with gas, the crankcase probably is full of gas too. all this is probably caused by an air leak between the mafs and the throttle body. check well all the turbo hoses including the intercooler for leaks. the compression is probably so low since by now the oil is so full of gas it's too thin. change the oil, put good plugs, eliminate the air leak.

 

Pulled timing covers off . Timing was dead on. Puy brand new plugs in- no luck again. tested my temp sensor and meter said 3.44 I also tested a used one and got 3.13 Is that enough of a difference that it would just be flooding the vehicle with gas? Temp is in mid 60's.

 

Check if there is a faulty grounding to the injectors thus keeping them open all the time,dumping in fuel and clogging your engine. Some wire may have coroded or broken and caused this.

 

the injectors are grounded via the ECU control output to turn them 'on'. they get their power from the radio suppression relay on 740/940 and from the fuel injection relay on 240. the grounds that are near the injectors on the intake manifold are just general grounds for the system, they aren't actually involved with the injector circuit.

 

I took the head off this mornig, an as I had started suspecting (because everything else worked), the head gasket went between cylinders 2 and 3. Having head dipped and planed- pickin it back up tomorrow. The car should now be tuned up nice and ready to go. Here's to no problems with the head! Many thanks for all of your help. This site has been a terrific resource.

 

Does anyone know what the head bolt torque should be?I was told it was in three stages but dont know what each torque setting should be.

 

stage 1 - 20 Nm (15 ft-lbs),
stage 2 - 60 Nm (44 ft-lbs)
stage 3 - an additional 1/4 turn (90 degrees)

theres a specific tightening pattern too.

as viewed from the right side of the car (the exhaust manifold side), looking down at the engine...

7 3 1 5 9

8 4 2 6 10