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Old 02-14-2020, 07:09 PM   #1
Kevolvo740
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Default 740 Turbo drives like it is rev limited

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?
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Old 02-14-2020, 09:07 PM   #2
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What have you checked?

I'd start with monitoring fuel pressure under load.
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Old 02-14-2020, 09:18 PM   #3
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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.
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Old 02-14-2020, 09:33 PM   #4
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Forgot to mention that I replaced the ECT sensor with a new Bosch unit.
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Old 02-14-2020, 10:12 PM   #5
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Mine does this too. I think it is a flaky MAF.
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Old 02-14-2020, 10:20 PM   #6
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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.
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Old 02-16-2020, 03:21 AM   #7
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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.
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Old 02-16-2020, 10:08 AM   #8
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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.
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Old 02-16-2020, 11:58 AM   #9
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Have you checked the fuel pressure regulator diaphragm?
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Old 02-16-2020, 01:11 PM   #10
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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?
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Old 02-16-2020, 01:43 PM   #11
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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.
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Old 02-16-2020, 05:41 PM   #12
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or just use a cheap tire pressure gauge.
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Old 02-16-2020, 05:54 PM   #13
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My fuel rail doesn't have a shrader valve. I think the later rails do have it.
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Old 02-16-2020, 06:37 PM   #14
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Right that is why you use the adapters. There was a recent thread with some part numbers for the adapters.
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Old 02-16-2020, 07:26 PM   #15
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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.
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Old 02-16-2020, 09:15 PM   #16
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Default fuel pressure testing on a rail without shrader valve

OK here are a few old threads I found. Hope this helps.
S & G Tool Aid 58012 14mm Volvo Lh-jetronic Adapter.
https://www.brickboard.com/FAQ/700-9...essureTestTool

https://forums.turbobricks.com/showthread.php?t=331683

http://forums.turbobricks.com/showthread.php?t=278712
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Old 02-16-2020, 09:52 PM   #17
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This is very helpful. I do have a spare rail somewhere. I think I can right something up using this info. Thank you.
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Old 02-21-2020, 11:17 AM   #18
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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.
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Old 02-21-2020, 06:33 PM   #19
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The issue is NOT your wastegate.
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Old 02-23-2020, 03:55 PM   #20
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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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Old Yesterday, 10:35 AM   #21
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I guess I was getting my hopes up about the wastegate. I couldn't get it over 2500 at idle, shut it off and messed with the wastegate linkage and within a minute restarted it and got my revs back. Whatever is rev limiting it seems to correct itself when I shut it off and restart it. Does that mean anything?
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Old Yesterday, 10:45 AM   #22
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I do have a known tested AMM coming and a fuel pressure regulator coming any time now. Hopefully one of those helps.
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Old Yesterday, 11:11 AM   #23
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It never hurts to do a solid tuneup as well. Clean injector grounds, clean resistor pack for injectors (VERY important since it is susceptible to constant moisture and corrosion. I have fixed multiple poorly running or non running 7/9 cars like this).

Plugs, wires, cap and rotor. All things that are probably overdue for replacement anyway. It's not firing the parts cannon either.
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Old Yesterday, 11:32 AM   #24
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Cap, rotor and plugs are new. Not the wires. Main under car fuel pump and filter are new. All this was replaced by the Volvo shop. Also the timing was checked. They did get it to the point where it starts and runs. But still have the intermittent rev limiting and fluctuating idle. I will now look at the grounds and injector resistor packs too, now that you mention it.
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Old Yesterday, 12:37 PM   #25
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Does this issue change with weather at all? Cold vs warm, humid vs dry?
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