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740 Turbo drives like it is rev limited

K

Kevolvo740

Member
Joined
Mar 29, 2013
I have a strange problem with my 1987 Volvo 740 turbo. It runs like it has a rev limiter. Sometimes, it starts and drives properly then begins to slow down and not respond to my foot on the pedal.

Put it in park and won't rev over 3000. Shut it off and leave it for 10 minutes and restart and it returns to normal. Then rev limits again after driving longer. Also has an idle that stays at 1000 then jumps to 1500 and back down. Any ideas?
 
Bit of a long story. Wouldn't start one day. It's winter too cold to work on it myself. Took it to a local Volvo expert. He said fuel pump was bad. He replaced the main under car fuel pump and filter. He also replaced the cap rotor and plugs. He also checked and set the timing. After all of this, the car would start but only if I hold the pedal to the floor. He told me that is what I have to do. I am not taking it back to him to throw more parts at it. But he did get it to the point that it starts and runs. It was fine for a while as I started it with my foot on the floor but now it has started this rev limiter issue. Also erratic idle.

I've read similar issues that blame a plugged cat or stuck turbo but this car goes back to normal when it sits for 15 minutes. Then starts rev limiting again when it has been running for about 30 minutes. This is consistent.
 
From googling, I'm seeing things that seem to point to the ECU as a possibility. I'm just starting to learn things about these older LH 2.2 cars. But I have a long way to go. I'm trying to understand why the car rights itself after sitting for a while. I will follow up on the fuel pressure and MAF as suggested so far.
 
I had this problem on my 86 240 and it was low fuel pressure. I thought I had ruled out fuel pressure when I replaced the lift pump, the failed main fuel pump and fuel filter. But the issue quickly recurred. Turns out the fuel filter was plugging very quickly due to rust in my fuel tank. I ended up treating the tank with acid and replacing the fuel filter and it solved my problem.

See what your fuel pressure drops to while the thing is falling on it’s face.
 
I think my car has the opposite problem. Too much fuel when trying to start it. One thing that helps on really cold mornings is for me too pull the number 1 fuse for the fuel pump. Then just as it starts to fire I hold my foot down and put the fuse back when the cylinders clear.
 
I pulled the vacuum line of and no fuel comes out and I don't smell fuel. Is there anything else I can do to check if it is OK?
 
You would want to do a fuel pressure check at the rail. There are adapters so you can connect a fuel pressure gauge to the input to the fuel rail.
 
Thank you. I'll look for that thread on fuel pressure adapters. A few people on this thread are suggesting that my issues seem like fuel supply.
 
This is very helpful. I do have a spare rail somewhere. I think I can right something up using this info. Thank you.
 
Update on my issues. I think that I have a couple different issues going. This morning I started it. Really cold out. Wouldn't rev over 2500 at idle. I shut it down. I reached under the turbo and felt the wastewater rod and lever. It felt crusty. I moved the rod up and down a bit where it connected to the lever. Restarted the car and it immediately revved up. Had it's power back on the road.

It still doesn't start well and has a weird idle. I'm waiting for a couple things to be shipped that were suggested here. AMM and fuel pressure regulator. I will clean up and lube the wastewater rod when it warms up a bit outside and hope this is the answer to my rev limit issue.
 
Wastegate is unrelated the free revving issue unless by some crazy occurrence your turbo is seized and the engine cannot breathe. Highly doubt that's your issue.

More times than not, it's a secondary ignition problem on these old distributor driven cars. They do not like humidity.

Fuel pressure would be the second culprit IMO.
 
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