Hi, my 91 740 is getting kind of hard to start. I crank it for a few seconds and it doesn't pop off at all. Then if I crank it again for a few seconds it will sometimes hesitate and then fire up, but almost always on the third try it'll fire up. When it does finally start it hesitates/misses a little and then it smooths out (relatively) at 700 rpm. It has a SMALL miss at idle, too. I've checked the fuel pressure regulator several times and it holds vacuum, I've changed the plugs, wires, cap and rotor, intake manifold gasket, alternator and ground wire, and the battery. It seems to "perform" okay and when using regular gas usually gets between 22 and 27 mpg highway. Any ideas where to begin? I know one thing for sure, that it has the "bendix/regina" fuel/ignition.

 

Where is the schrader valve?

 

Ok.... so how about some advice? The reason I even asked is because I want advice specific to my particular vehicle. If you have nothing to offer other than general "advice" that is vaguely related to my car...and every other car out there than keep your comments to yourself. I was a mechanic at a saturn dealership for 7 years, so I know GM cars pretty well, and ever since I started driving I've owned Ford cars and trucks. HOWEVER, this IS the first volvo, the first european car, and thee first vehicle I've ever owned that wasn't a Ford. Maybe you're not aware, but the resources available to volvo owners is pretty limited in comparison to domestic vehicles. Help me if you can, if not then don’t even bother!

 

OK..you have nailed all the obvious probs (plugs wires gaskets fuel pressure etc). It should start after about 3 seconds of cranking, so if it was me I would test the temp sensor, as it might be under/overfuelling from cold, which would account for the intial rough idle. I can't remember the resistance readings, but they are somewhere on the net. I yanked a couple out of scrap cars and compared them with mine and stuck them in water and found that mine was out, so it thought it was 40 degrees below so it flooded all the time.

The main sensor is (facing the car) on a 2.0/2.3 Litre on the right under the intake manifold. Also, these cars in Europe have a blue plastic edged metal start injector, which squirts in the initial burst of fuel. The start injector is easy to remove and test with 12V. You can either test when cranking (still connected but removed from the intake) or you can bench it and it clicks loudly. Once other fault (which is rare) is that the start injector seal can fail and they drip fuel into the intake, which cab make it hard to start.

If it was me, this is what I would try next. The fuel economy does not sound great...how hard to you hit the pedal? If you are doing a steady 60mph, the redblock should do 30-35 on long trips and around 20-22 around town. UK gallons a a bit larger, but 22-27 on the highway sounds a bit high, but it does depend on driving style of course.
Hope this helps

 

Ects...didn't think of that one. I'll check for the correct ohms and take a look at it. I thought 22-27 us mpg was pretty good considering it got 18 when I bought it until I fixed the intake gasket and the leaking return line...

 

I looked up that US gallons are about 15% smaller than UK gallons, so your 22-27 mpg would be around 25-31 (ish) in UK mpg. As I said, it depends on your driving. In the UK they used tell us to check economy by brimming the tank and run nearly to dry and then brim again and divide the miles by the fuel used. However, it would cost me nearly $100 eq to fill my tank, so I don't fancy it!

We have to buy our fuel in litres now anyway. We are soooooo ripped off. about 80% of the cost is tax.

I remember that the start injector is timed on the resistance of the sensor, so at minus 30C it delivers 7 seconds of fuel and at say at +25C it runs for 2 seconds or something like that.

 

22-27 is about right for a non-turbo 740.

To check the fuel pressure of a LH2.2/2.4 volvo, you need to disconnect the fuel line from the fuel rail and put the pressure gauge in line, this requires a specific thread adapter on your fuel pressure gauge.

a excellent set of 740/940 specific troubleshooting resources here
Volvo Maintenance Hints for 7xx/9xx/90

your 1991 should be a LH2.4, this has the onboard diagnostics via blinkbox that doens't require any external test equipment. see Engine and OBD Diagnostic Codes

 

That previous post is very useful, as the diagnostic list for LH 2.4 and teh Regina stuff hits all the bases in that link. I remember I found it a few years ago when my 90 940 was producing black smoke and guzzling fuel. I sat there fiddling with the diagnostic box and nothing happened at all. Everything on the engine was working fine (sensors, fuel etc etc) My symptoms did not fit any of the common ECU failures (like the one where it will not start the fuel pump). Eventually, I worked out it that the ECU had gone into Arctic mode due to water ingress which had shorted some components. I replaced it with a unit from a 2.0 litre (mine is a 2.3) which works. I then discovered then that the fault code box was not hooked up to the ECU as there was no connection to it out of the unit, so I was a bit non-plussed with that. Still, it cost me 25 quid from a scrapyard instead of 350-400 quid from Volvo. It did take me the best part of a couple of weeks to puzzle it out though.