I have a 1991 740. The current issue that I am having is that the car is acting like its not getting any fuel and sounds like crap. It kinda just happend all of a sudden but was running fine before that happend, i would give it gas but it wouldnt go. My guess is that its a sensor gone bad. I have replaced the fuel pump about a year ago, and can hear the whirring sound when I switch the car on. I also just replaced the Crankshaft position sensor because that has been giving me troubles as well. Any suggest will help.

 

Have you checked fuel pressure? There is a fp regulator that could go out.

 

a 91 740 should have the LH2.4 OBD code thing forward of the left shock strut, which can display both fuel injection (position 2) and ignition control unit (position 6) error codes.

Engine and OBD Diagnostic Codes

 

Funny that you bring this up. My wife told me this happened last week but only for a short period of time. The engine would run but no power. RPM would not increase in drive but would in neutral. Well it happened to me last night so I'll be out in the garage in about and hour to see if I have any codes. I stopped the car and let it idle and raced the engine. I then put it in drive and it ran fine. It starts and idles fine and all electrical stuff works. Last year I did new pump's , filters , both relays , crank sensor and it ran like a top. The fuel reg. is not leaking so I'm thinking somewhere in the TPS or Air mass . 1989 740 GL with 313K miles on it. I'll try to sort it out today.

 

No real news. No codes with both only showing 1-1-1's so whatever the problem is there was no CEL. I'll continue to diagnosis based on if/when it happens again. I just did some un/re-plugging of some of the connectors so we'll see. Considering when I stepped on the gas and the engine didn't increase rpm (in drive) but did when I put it in neutral I need to understand what is involved with the TPS , MAF and crank sensor during acceleration.

 

note that not all codes throw a CEL (Check Engine Light), for instance, my 92 740T likes to toss a 2-4-1(I think) EGR error without a CEL and I just haven't gotten around ot sorting it out yet.

TPS tells the ECU where the throttle is. MAF tells it how much air the engine is inhaling. crank position sensor tells it the engine is turning and provides the timing reference used by both the ignition and fuel ECU.

just because no fuel came out of the vacuum port on the FPR, that doesn't mean the FPR is working properly, it just means the diagphram isn't perforated.

try starting the car with the AMM/MAF (same thing) disconnected.... turns out the MAF's input is just used for fine tuning, and the car will run in 'limp' mode with out it, probably better than yours is running now.

try replacing the vacuum line to the fuel pressure regulator (its just generic euro vacuum hose cut to length). while you're at it, replace most all of the rest of the vacuum spagetti lines, they get tiny cracks after awhile and start leaking and all kinda stuff goes sideways.

 

pierce I don't know if you are talking to me or to silvervolvo. I just got back from an afternoon out and the car is running great as usual. No issues So I'll be trying to find this intermittent (happened 2 times) failure and then sort it out. I'll check a few of the item you identified and just see where it leads me.

 

We had a very similar problem with our 88 volvo 740. It would start, idle, and rev up fine, but put it into gear and try to go and it would cough, sputter, and almost die. Turned out the the cheap (carter brand) in tank fuel pump that was only 8 months old was quitting. Changed that pump (warrenty on the pump) and all was fine again for about 8 months again. Finally replaced it with a good pump and has not been a problem since.

Russ

 

well, FWIW, my 92 740T was running without a functional intank pump, the main pump was really noisy even at idle, and it would die if the gas was low, but with a full tank, it had nearly full power up 3000 or 4000 rpm in 2nd or 3rd gear... with the intank pump replaced, no more bogging at full throttle above 4000rpm. the fuel sock on the tank inlet was totally flugged up too, and was replaced as a matter of principle.

ps. getting those intank pumps in can be a real bear.

 

Thanks for the help. I will check the things mentioned and let you guys know what I came up with. And another question is if i can hear the fuel pump whirring sound, than could it still mean that its not working?

 

the best way to confirm the fuel pump is working properly is to A) test the fuel pressure (which requires a fuel pressure gauge and volvo specific adapters), you should get 43-44PSI with the FPR vacuum line disconnected, and about 7-9psi less than that at idle with it connected when the engine is running and B) disconnect the outlet line from the fuel pressure regulator, connect a temporary piece of hose that goes into a gallon jug, and jumper-run the fuel pump for as close to 10 seconds as you can count. you should get between 1/2 and 1.5 pints of gas.

of course, take all precautions about sparks and fuel when doing tests with the fuel system, being careless here is a good way to burn your car down.

also see
Engine: Fuel Injection
and
Fuel System: Pumps, Relays

for probably better advise than I gave above

 

Have you tried replacing the Radio Noise Suppression Relay? I hear this is often a surprising fix for such things.