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Old 12-05-2019, 05:36 PM   #1
daniels740
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Default Volvo 740 Runs Erratically

My 1989 740 Turbo has been running erratically for a bit of time now and it has really stumped me.

When I first start the car, when it cranks over, instead of a uniform dun-dun-dun starting noise, the engine makes a dun-dun-dah noise as if it does not make compression in one cylinder.

After it starts, it runs erratically accompanied with a small ticking noise. Then, suddenly, the noise goes away and the car runs perfectly smooth.

After that, if I were to start the engine again right after turning it off, the engine makes a uniform dun-dun-dun cranking noise before it starts.

The injectors, spark plugs, and the distributor are all new.

What could cause this problem? Any help is appreciated. Thanks.
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Old 12-05-2019, 05:38 PM   #2
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Do a cold compression test. I've had this happen before on mildly blown head gaskets. Once warm, the fire ring sealed up properly. When cold, it did not.
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Old 12-05-2019, 07:40 PM   #3
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Originally Posted by iHateVolvoPeople View Post
Do a cold compression test. I've had this happen before on mildly blown head gaskets. Once warm, the fire ring sealed up properly. When cold, it did not.
I don't know about the head gasket being the problem, the car's never lost a drop of coolant and it also sometimes (becoming less frequent) starts and runs perfectly even when the block is completely cold without showing any of these symptoms at all. Could it be a sticking valve?
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Old 12-05-2019, 07:49 PM   #4
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I don't know about the head gasket being the problem, the car's never lost a drop of coolant and it also sometimes (becoming less frequent) starts and runs perfectly even when the block is completely cold without showing any of these symptoms at all. Could it be a sticking valve?
It could be a multitude of things. And a blown head gasket at the fire ring will not always use/burn coolant. It depends where the head gasket 'blows'.

I have noticed on a few of my Volvo's (depending on the cam and the injection system) that on a cold motor they just lope or don't idle well. For me it only lasts 30 seconds or so.

I've had a sticking valve on a Redblock, but never one that's only present when cold. I doubt that is the problem.
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Old 12-05-2019, 08:03 PM   #5
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It could be a multitude of things. And a blown head gasket at the fire ring will not always use/burn coolant. It depends where the head gasket 'blows'.

I have noticed on a few of my Volvo's (depending on the cam and the injection system) that on a cold motor they just lope or don't idle well. For me it only lasts 30 seconds or so.

I've had a sticking valve on a Redblock, but never one that's only present when cold. I doubt that is the problem.
In that case, do you know what could cause the compression to go back within normal spec all of a sudden?

I have a feeling this is what is happening because of the noise when cranking. I remove the injector ballasts so the engine doesn't have fuel to start, that way I can hear how it is cranking. The engine goes from the irregular cranking sound (dun-dun-dah), when it runs erratically, to perfectly normal (dun-dun-dun-dun), when it runs fine, with no in-between, so that is why I feel it cannot be an issue with things heating up and expanding.

Now, I'm far from an expert on Redblock engines, so correct me if my inference seems incorrect.

Thanks for the help.
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Old 12-05-2019, 08:09 PM   #6
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The reason for come-and-go compression, in my case, was simply due to the expansion of metals as they warm up.

Your problem could be that but could be so many other things. You could try reading all 4 plugs. Perhaps 1 of the 4 injectors is leaking and washing down the cylinder and filling it with liquid (incompressible), which would create a weird sounding engine as it cranks. But it would create excessive cylinder pressures rather than being low on compression).

I would certainly do a cold compression test for your case. Make sure to unplug crank sensor or hall sensor+injectors, and hold throttle WOT. Also make sure battery is good. If it isn't, have jumper cables hooked up to produce more accurate results.
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Old 12-05-2019, 08:16 PM   #7
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The reason for come-and-go compression, in my case, was simply due to the expansion of metals as they warm up.

Your problem could be that but could be so many other things. You could try reading all 4 plugs. Perhaps 1 of the 4 injectors is leaking and washing down the cylinder and filling it with liquid (incompressible), which would create a weird sounding engine as it cranks. But it would create excessive cylinder pressures rather than being low on compression).

I would certainly do a cold compression test for your case. Make sure to unplug crank sensor or hall sensor+injectors, and hold throttle WOT. Also make sure battery is good. If it isn't, have jumper cables hooked up to produce more accurate results.
A compression test certainly seems like a good idea. Hopefully I'll get back to this thread with my readings by Saturday night. I'm still open to other ideas and opinions.
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Old 12-05-2019, 08:29 PM   #8
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If the engine physically CRANKS with a different rhythm, then I'd say you have a compression issue, or a really weird power/current delivery to the starter.
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Old 12-05-2019, 08:34 PM   #9
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If the engine physically CRANKS with a different rhythm, then I'd say you have a compression issue, or a really weird power/current delivery to the starter.
It would be far too large of a coincidence to be an electrical issue delivering power to the starter.
In my opinion, it is a compression issue; only that I have no idea why it is behaving the way it is.
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Old 12-05-2019, 09:05 PM   #10
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It would be far too large of a coincidence to be an electrical issue delivering power to the starter.
In my opinion, it is a compression issue; only that I have no idea why it is behaving the way it is.
I agree keep up posted
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Old 12-06-2019, 06:38 PM   #11
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I just checked the compression with the engine cold.

The second cylinder was exactly 150 psi.
The third was at about 148-150 psi.
The fourth was at exactly 160 psi.

The first cylinder was another story. When I first checked it, it was at exactly 0 psi. I proceeded to check all the rest and then I put all the plugs back on. Then, the started right up.

Seeing this, I shut the engine almost immediately so it wouldn't warm up at all, and then I checked the first cylinder again. It read exactly 150 psi.

This sounds like a stuck valve to me. What are your opinions?
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Old 12-06-2019, 08:37 PM   #12
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I just checked the compression with the engine cold.

The second cylinder was exactly 150 psi.
The third was at about 148-150 psi.
The fourth was at exactly 160 psi.

The first cylinder was another story. When I first checked it, it was at exactly 0 psi. I proceeded to check all the rest and then I put all the plugs back on. Then, the started right up.

Seeing this, I shut the engine almost immediately so it wouldn't warm up at all, and then I checked the first cylinder again. It read exactly 150 psi.

This sounds like a stuck valve to me. What are your opinions?
That actually does sound like a temporarily stuck valve to me.

When mine were getting stuck, I beat them free (3 out of 4 intake valves were glued open) and then threw in 3qts clean oil and 1qt atf. Beat the **** out of the car for a few miles then changed to t6. Never had a single issue with the car after that.

You don't really need to beat on it, but I wanted it to get warm. Heat is good. 200f oil is really good.
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Old 12-07-2019, 12:13 AM   #13
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That actually does sound like a temporarily stuck valve to me.

When mine were getting stuck, I beat them free (3 out of 4 intake valves were glued open) and then threw in 3qts clean oil and 1qt atf. Beat the **** out of the car for a few miles then changed to t6. Never had a single issue with the car after that.

You don't really need to beat on it, but I wanted it to get warm. Heat is good. 200f oil is really good.
So, I should replace the oil with the oil+ATF mixture, and then drive it a bit more aggressively to get the oil hot? Is there a specific oil viscosity best for this? And do I keep the oil/atf mixture in the engine for a while for it to take its effect or do I replace it rather quickly?

Sorry for all the questions and thanks for all the help.
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Old 12-07-2019, 12:39 AM   #14
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“then threw in 3qts clean oil and 1qt atf”

Don’t fuss this too hard, regular , say 10w30, and ATF, then drive a while. 100kms? Then change it. It’s an old engine , good luck .
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Old 12-07-2019, 12:41 AM   #15
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“then threw in 3qts clean oil and 1qt atf”

Don’t fuss this too hard, regular , say 10w30, and ATF, then drive a while. 100kms? Then change it. It’s an old engine , good luck .
Alright, I'll do that then. Thanks.
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Old 12-07-2019, 09:53 AM   #16
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IIRC, ATF is pretty thin so you would want to run a thicker oil like 10w-30 as suggested above.

My advice is simply what worked for me. It may or may not work for you, assuming a stuck valve is your problem. Best of luck!
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Old 12-07-2019, 04:20 PM   #17
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The reference was to 3 qts oil and one qt ATF. Then a short interval and change the oil again. The OP should check the owners manual for amount of oil and the specified grade and type.
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Old 12-11-2019, 02:35 PM   #18
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try changing the spark plug leads, my K-jet 2.4 redblock used to start on three cylinders only for the first 10 seconds or so on some days and would ping in hot weather.
Changed the leads and now its fixed.
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Old 12-28-2019, 10:59 PM   #19
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Update: I did an oil change with 20% Marvel Mystery Oil and the rest 15w-40 oil (Not too thick cause its not cold down here + the MMO lowers the viscosity), and since that oil change, with no CRAZY driving, I haven't had a problem since. No more sticky valves. I haven't ever been too fond of these "snake-oils," but MMO really is amazing.

I've always heard good things about MMO, and I can now testify to the powers of that mysterious, great-smelling oil. I hope this thread can help anyone else with similar issues.
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Old 12-29-2019, 10:37 AM   #20
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Update: I did an oil change with 20% Marvel Mystery Oil and the rest 15w-40 oil (Not too thick cause its not cold down here + the MMO lowers the viscosity), and since that oil change, with no CRAZY driving, I haven't had a problem since. No more sticky valves. I haven't ever been too fond of these "snake-oils," but MMO really is amazing.

I've always heard good things about MMO, and I can now testify to the powers of that mysterious, great-smelling oil. I hope this thread can help anyone else with similar issues.
Realistically, ATF, MMO, seafoam, etc all probably would have done the job. Even a good quality synthetic and some spirited driving may have. But I'm glad you got it fixed!

I would not run the MMO for the entire oil change interval since we have no idea what it lowered the viscosity to.
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