740 1990 lags starting off/almost stalls

Jonnyk · Post by **Jonnyk** » 07 Apr 2009, 21:29

I have found so many great answers here. Many of you have helped me get my 740 running better. MY current problem is this. The car lags when starting from a complete start, or turning, as if the fuel is trying to catch up. Sometimes the car really pulses and bucks. I find that when I back off the gas a little the car catches up and I'm good unless i have to slow down or stop completely. This is obviously not the safest thing to encounter in Orlando traffic. Prior to this condition, my in-tank pump died. I replaced the pump and a relay that had crapped out, replaced the original fuel filter, replaced the plugs and wires. I would love to fix this on my own, but worry that the problem might be more advanced.

Post by **billofdurham** » 08 Apr 2009, 15:33

What you are describing are typical symptoms of a bad in-tank pump. As you have replaced the pump check the wiring connections to it as the old connectors may be dirty.

Which filter did you replace, main or in-tank?

Do a search for 'fuel pump' with author Kmaniac in California USA. Chris has done a good write up of his experiences and you will find a lot of good advice on this subject.

Bill.

Jonnyk · Post by **Jonnyk** » 08 Apr 2009, 18:16

I replaced the in-tank pump. My 740 has only the one pump. When I soldered the wires to the new pump I ran a continuity test and from top to bottom I no wavering. This of course doesn't mean that the continuity wasn't low to begin with. I will go back over the posts you mentioned. They were a great help when I cracked the tank the first time.

Jonnyk · Post by **Jonnyk** » 17 Apr 2009, 07:37

I cleaned the wire connections. The car now has moved on to revving 1500-2000rpm-just for asecond- when in neutral, and dropping to @750rpmwhen put into drive or reverse. I wonder if my timing is all screwed up. Everything happened after the fuel pump was replaced. Also I must note that the lagging and even stalling (once) has gotten worse as time has progressed.

So, new pump,relay, fuel filter,plugs,wires.

Thanks for any help on this.

GSmith · Post by **GSmith** » 17 Apr 2009, 08:29

Jonny,

I'm not a Volvo pro by any stretch of the imagination (I've only owned mine for a week), but I can say that my friends who own Fords have similar problems when their oxygen sensor goes bad. Are there any dash lights on? Maybe search these boards to see if anyone has had similar problems with the O2 sensor?

G

Jonnyk · Post by **Jonnyk** » 17 Apr 2009, 10:00

I will look into. I am going to check my fuel pressure at the rail as well. Could be the replacement pump isn't up to snuff.

Post by **billofdurham** » 17 Apr 2009, 15:22

Out of curiosity which engine is this?

Have you checked the throttle switch and its connector? This can cause misfire, incorrect/erratic idle and other faults. Also check all vacuum pipes and the earth (ground) terminals on the intake manifold.

Bill.

Jonnyk · Post by **Jonnyk** » 20 Apr 2009, 07:52

Thanks.

Tiki · Post by **Tiki** » 21 Apr 2009, 00:14

This is interesting. I stumbled across this forum looking for radio codes because I had to disconnect the battery when I pulled my fuel pump in the tank.
My car, a 760 with the V6 was doing almost what yours is doing.

Simple test for you, clamp off the fuel return line from the Fuel Pressure Regulator. It should be at the end of the fuel rail. If the symptom clears up then you have either a bad FPR or a restriction in the line. In my case I suspected a restriction as the FPR was not that old. I had also changed the fuel filter chasing this problem so I knew it was not that.
What I found was the pickup screen at the bottom of the tank was crushed. The float is spring loaded and presses it to the bottom of the tank. I reshaped it as it was Sunday and no replacement could be found. The car works good. I ordered a new one.

My manual suggests clamping the return line with a pressure guage attached. If the pressure jumps up to max it's the FPR. If it climbs slowly it's a restriction. I didn't have a guage so I had to guess.

Good luck!

Jonnyk · Post by **Jonnyk** » 21 Apr 2009, 11:26

Problem solved! The fuel pump didn't have enough pressure. It was the right size pump, just wasn't a good pump. The pump was replaced and everything has been fine. I will say that through these posts I was able to track down and correct most of my problems. Thanks everyone.