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My 1988 Volvo 740 GL 2,3 non-turbo has attracted an issue. After a 250 km drive it started to lose power under acceleration.
It started doing it just a little, where I could feel a slight hesitation at around 3000 rpm. I didn't really think about it.
When I drove on after a couple hours break, it came back, only worse, and suddenly it wouldn't go above 2500 rpm / 30 km/h, with the throttle floored. I pulled over and let it idle for a bit, revved it up to 5000 and everything seemed like it was back to normal.
After around 40 km on the highway, where everything seemed fine, the problem came back - and now the car actually died. Once again I pulled over, let it sit for a while and tried to start it, but it would only run very roughly with just a few hundred rpm, very shaky and with no response from the throttle. I put about 5 litres of gas in the tank (the fuel gauge doesn't work), and after 3-4 tries and a couple of minutes I got it running - but I had to keep the pedal to the metal for 30 seconds before it got running properly and was able to stay idling.
However, on the last 10 km of my trip there was still some hesitation/power loss under acceleration. Sometimes it wouldn't go over 3000 rpm, but when I did manage to get it over and rev it up to 5000, that seemed to make the problem go away for a little while.
What could cause this?
I feel like the problem might be fuel related. Could it be a dying fuel pump?
But then again, if it was the pump, why would it help to rev it to high rpm?
Bonus info:
Within the last couple of weeks the following parts have been replaced:
Front part of the exhaust pipe (used) and cat (new)
The whole in-tank assembly with pump and sensor (used)
The fuel pump relay is 6 months old.
Plugs, cables, air filter and rotor was replaced 3 months ago.
I have felt a bit of hesitation before sometimes during acceleration, but it has been very rare with weeks in between and only once/twice and then it's gone away.
The fuel pump under the car sounds like this - does that sound healthy?
I was told it could be related to the in-tank pump or fuel filter. Someone said that the in-tank assembly might have been installed "facing the wrong way" by the mechanic, causing the car to run out of gas when there was still plenty in the tank. I removed the access plate and took a look, but I think it looks like it's correctly installed?
That pump does not sound healthy. Considering the history, it does sound like a fuel related problem. The picture of the tank pump connections shows some modifications to wiring and such but impossible to tell if it is "correctly" installed.
Sounds like 2 issues at once my friend! I once had a terrible wiring job done to my main fuel pump, whuch was also a weak airtex fuel pump sounded way louder than that but lasted like 5 years! Check your Tps Osss
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That pump does not sound healthy. Considering the history, it does sound like a fuel related problem. The picture of the tank pump connections shows some modifications to wiring and such but impossible to tell if it is "correctly" installed.
The assembly at the tank was lifted from a later model (and I think a 940). I think that’s why the connectors look different.
I will check the throttle position sensor. Any tricks to troubleshoot the pumps? Or do I just have to change them and hope it fixes the problem?
I would maybe check fuel pressure??? If you dont have tool then focus on revving engine up to 2k then 3k then release gas see if rpms drop slowly and steadily.
2. Pull in tank fuse for a quick second while car is running and listen to sound changes! Start there... osss
But don’t those methods require the problem to be present right now? It seems the problem is gone right now, so I don’t know how to troubleshoot it now... The thing is I have to decide whether I should try to drive the car the 300 km back home or leave it here (currently visiting my parents) and get the train back home and come back for the car some other time.
A 940, post 1992, has a bigger tank, some 21gallons vs, 15.8 for a 740, apart from that I believe the pump/sender unit is the same as long as it's Bosch and Regina differentiated.
Is your gas gauge showing correctly? If your fuel level is low, like below half a tank, and you are experiencing these issues, you may have an in tank hose split which causes fuel starvation. Fill it up and see if the problem goes away--it's a possibility.
Well i have an extremely rare bosch/ regina 1989 hybrid!! I have rex coil and also fuel pump under the car! I have experimented with unplugging intank fuse with tank well into Empty... Absoultely no change! Runs perfect!! I think you may have to just get a fuel pressure test... Otherwise your guessing. In addition, change out your fuel filter too! Oss from Hotlanta!!!
Is your gas gauge showing correctly? If your fuel level is low, like below half a tank, and you are experiencing these issues, you may have an in tank hose split which causes fuel starvation. Fill it up and see if the problem goes away--it's a possibility.
My fuel gauge did not work at all before I gave it to the mechanic who replaced the in tank assembly - it was always at zero.
But after it was replaced, the gauge has started behaving differently. It does not show reliable information. When the tank is full, the gauge shows around half full. The needle moves around a lot depending on how the car moves.
Also, as mentioned earlier, the problem did seem to go away after filling it up - but I wasn’t sure if it was the filling up that helped or if it was just letting the car sit for a days time. But sounds like there might be something there???
I just pulled fuse 11, which I think is supposed to be for the in tank pump. There was no change in sound, revs or throttle response. So I guess that means that the in tank pump is dead? Could that be what’s putting stress on the external pump, causing it to sound like that?
I also reved the car first to 2k, then to 3k, and the revs fell smoothly down to idle.
But I don’t really understand the behavior of the car if the in tank pump is simply dead. Then why would it lose power, then stall, then run with limited power/hesitation, and then after 20 hours and some extra fuel, run fine?
Could be vapor lock! Happens when tank is low and if intankpump is iffy! Whomever did your intank pump have them re check it out! Also change out your radio supression relay underhood. They can run intermittent and cause all types of problems!! Also let car run for like 10 min idle then turn engine off. Undo gas cap, if you hear a loud vapor whoosh sound...could be vaporlocking!! Osss
Fuel pumps can be erratic, work for a bit then not, etc. If your tank pump is inop then the main pump will be working too hard (heard about that, not personal knowledge), and hence the noise it makes? It does look like the sender is wrong, from a later 940...
10-20-2018, 03:37 AM
740 power loss/car died - fuel related?
