91 240se +t subtle power oscillations

intothelabyrinth · 06-06-2022, 04:44 PM

I recently completed a +t on my 92 240se wagon. The thing seems to run great, and rips hard. Starts every time, and never even thinks about stalling. Great idle... I noticed yesterday that the power seems to slightly oscillate at moderate throttle inputs. Like, if I step on it it rips hard and I have no problem hitting almost 14psi. But when I'm cruising I can feel a constant, subtle, pulse that I see on the vacuum gauge as well. I am thinking it must be misfiring? I am going to test fuel pressure, and see if that is in spec, as well as really check over everything for vacuum leaks. What does that sound like to you guys?

ZVOLV · 06-06-2022, 05:32 PM

Air leaks are likely. I'd do a smoke test.

intothelabyrinth · 06-10-2022, 09:03 PM

Smoke test yielded no leaks, not even brake booster or evap. Fuel pressure next. It seems to be getting worse. Just not an even power delivery.

dl242gt · 06-11-2022, 01:04 PM

Have you upgraded the intank pump? The stock one can be a little weak to supply a turbo engine. Volvo spec'd a more powerful pump for the 740 turbos and you can install that in the 240. I think that's the ipd upgrade kit they sell.

intothelabyrinth · 06-12-2022, 09:47 AM

Nah, I haven't even touched the fuel system yet. Probably should do the filter and look in the tank. 740 turbo in tank pump is probably a good idea. I'm thinking it has to be fuel related.

intothelabyrinth · 06-26-2022, 12:44 PM

Ok so I finally got around to investigating this. Hooked up my homemade fuel pressure gauge and it's working great! Got a reading of 45 psi running pumps with engine off. With engine running I get 45 psi with vacuum to fpr disconnected and when I plug it up its rapidly bouncing from 35-38. This was a bit of an aha moment for me. My boost gauge has always fluttered and I thought it was just the gauge! But now I know that it is indeed engine vacuum fluttering, causing the fuel pressure to flutter as well. Under boost this goes away and it rips smooth because with no vacuum the fuel pressure is steady full blast!

This leads me to investigate the cause of my fluttering vacuum. I'm thinking, check timing and do a compression test? Maybe valves need adjustment, or my cam timing is off?

ZVOLV · 06-26-2022, 01:27 PM

It sounds like a misfire could be the issue.

How'd you perform the smoke test? A small airleak could cause you to go lean at cruise and misfire.

Maybe start with a good cap, rotor, plugs and wires if they haven't been done in a while.

Maybe try another MAF too.

intothelabyrinth · 06-26-2022, 01:28 PM

I forgot I had the boost gauge dampened. I took that off and it oscillates even under boost.

intothelabyrinth · 06-26-2022, 01:31 PM

I made this awesome smoke tester that puts pressurized smoke into a vacuum port.

intothelabyrinth · 06-26-2022, 01:34 PM

Im almost thinking that it could be a burned valve. The vacuum at idle is bouncing super fast.

ZVOLV · 06-26-2022, 01:35 PM

I'd be interested to see pics of smoke machine. If you are just going into a vacuum port, that sounds like you aren't really smoke testing the entire induction system. You may wanna do a good strong smoke test starting close to the turbo.

IC hoses leak commonly, idle air hoses leaks commonly at the ends of the hoses, soggy MAF intake hose can leak at the bottom, etc.

Quote:

Originally Posted by intothelabyrinth

Im almost thinking that it could be a burned valve. The vacuum at idle is bouncing super fast.

Perform a leak down test.

intothelabyrinth · 06-26-2022, 01:35 PM

I'll check my plugs and see if they tell me anything. I can also do a compression test.

intothelabyrinth · 06-26-2022, 01:38 PM

I was putting 5psi of smoke into the evap port on the throttle body. It filled up the whole intake and started coming out the air filter. Now that I think of it, that wouldn't really put smoke out the intake manifold gasket would it! Do that again and open the throttle?

intothelabyrinth · 06-26-2022, 01:40 PM

Im gonna smoke test again. Any tips on where to plumb the smoke in?

ZVOLV · 06-26-2022, 02:00 PM

You could cap off the intake hose at the MAF, crack the throttle and try again. Maybe something will show up that didn't last time.

Another trick is spraying around with brake cleaner at idle and seeing if you can get the engine to stumble. On modern cars, I spray around with brake cleaner and monitor fuel trims with a scan tool to find air leaks. It works well.

intothelabyrinth · 06-26-2022, 04:13 PM

Pulled the plugs and they all looked fine and the same. Tested compression dry and got
Cyl 1 143
Cyl 2 150
Cyl 3 150
Cyl 4 146

Changed plugs to bpr7es and put on new wires.
No charges.

Leakdown test next. I'm really starting to suspect a burned exhaust valve. This had to have happened before I got the car because the bouncing vacuum deal was there from the moment I put the boost gauge on, which was before the +t was used at all. Maybe the po rode around with a vacuum leak forever?

06-06-2022, 04:44 PM	#1
intothelabyrinth Board Member Join Date: Mar 2012 Location: Bowling Green, KY	91 240se +t subtle power oscillations I recently completed a +t on my 92 240se wagon. The thing seems to run great, and rips hard. Starts every time, and never even thinks about stalling. Great idle... I noticed yesterday that the power seems to slightly oscillate at moderate throttle inputs. Like, if I step on it it rips hard and I have no problem hitting almost 14psi. But when I'm cruising I can feel a constant, subtle, pulse that I see on the vacuum gauge as well. I am thinking it must be misfiring? I am going to test fuel pressure, and see if that is in spec, as well as really check over everything for vacuum leaks. What does that sound like to you guys? __________________ 1986 245 Auto (RIP) 1986 245 Auto (RIP) 1988 245, M47 1989 245 Auto California Car (sold) 1993 245 Classic (Bro's Daily) 1988 245 (turbo manual swapped) 1990 245 (getting turbo manual swapped) 1991 245se (rat rod project, turbo aw71 swap) 1969 164 (trying to make it run) Instagram

06-06-2022, 05:32 PM	#2
ZVOLV <Master Tech> Join Date: Nov 2002 Location: California	Air leaks are likely. I'd do a smoke test. __________________ No Start Thread

06-11-2022, 01:04 PM	#4
dl242gt Old and boxy but good. Join Date: Jun 2002 Location: S NJ, a suburb of Phila.	Have you upgraded the intank pump? The stock one can be a little weak to supply a turbo engine. Volvo spec'd a more powerful pump for the 740 turbos and you can install that in the 240. I think that's the ipd upgrade kit they sell. __________________ Dave, 1982 242 turbo. 338k miles. MVP coilovers and 3" exhaust. Flowed 405 with a V15. Cossie turbine housing with upgraded compressor housing. 90+, IPD remote oil filter. Some other goodness, too. Been lots of fun over 25 years. Restored in 2k. Now ready for a 2nd restoration. 1993 245 Classic, 440k miles, enem V15. IPD bars and chassis braces. Simons sport exhaust from Scandix. sbabbs ezk chip. Been a good road warrior. Genuine Volvo rebuilt leaky M47.

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06-10-2022, 09:03 PM	#3
intothelabyrinth Board Member Join Date: Mar 2012 Location: Bowling Green, KY	Smoke test yielded no leaks, not even brake booster or evap. Fuel pressure next. It seems to be getting worse. Just not an even power delivery.

06-12-2022, 09:47 AM	#5
intothelabyrinth Board Member Join Date: Mar 2012 Location: Bowling Green, KY	Nah, I haven't even touched the fuel system yet. Probably should do the filter and look in the tank. 740 turbo in tank pump is probably a good idea. I'm thinking it has to be fuel related.

06-26-2022, 12:44 PM	#6
intothelabyrinth Board Member Join Date: Mar 2012 Location: Bowling Green, KY	Ok so I finally got around to investigating this. Hooked up my homemade fuel pressure gauge and it's working great! Got a reading of 45 psi running pumps with engine off. With engine running I get 45 psi with vacuum to fpr disconnected and when I plug it up its rapidly bouncing from 35-38. This was a bit of an aha moment for me. My boost gauge has always fluttered and I thought it was just the gauge! But now I know that it is indeed engine vacuum fluttering, causing the fuel pressure to flutter as well. Under boost this goes away and it rips smooth because with no vacuum the fuel pressure is steady full blast! This leads me to investigate the cause of my fluttering vacuum. I'm thinking, check timing and do a compression test? Maybe valves need adjustment, or my cam timing is off?

06-26-2022, 01:27 PM	#7
ZVOLV <Master Tech> Join Date: Nov 2002 Location: California	It sounds like a misfire could be the issue. How'd you perform the smoke test? A small airleak could cause you to go lean at cruise and misfire. Maybe start with a good cap, rotor, plugs and wires if they haven't been done in a while. Maybe try another MAF too.

06-26-2022, 01:28 PM	#8
intothelabyrinth Board Member Join Date: Mar 2012 Location: Bowling Green, KY	I forgot I had the boost gauge dampened. I took that off and it oscillates even under boost.

06-26-2022, 01:31 PM	#9
intothelabyrinth Board Member Join Date: Mar 2012 Location: Bowling Green, KY	I made this awesome smoke tester that puts pressurized smoke into a vacuum port.

06-26-2022, 01:34 PM	#10
intothelabyrinth Board Member Join Date: Mar 2012 Location: Bowling Green, KY	Im almost thinking that it could be a burned valve. The vacuum at idle is bouncing super fast.

06-26-2022, 01:35 PM	#12
intothelabyrinth Board Member Join Date: Mar 2012 Location: Bowling Green, KY	I'll check my plugs and see if they tell me anything. I can also do a compression test.

06-26-2022, 01:38 PM	#13
intothelabyrinth Board Member Join Date: Mar 2012 Location: Bowling Green, KY	I was putting 5psi of smoke into the evap port on the throttle body. It filled up the whole intake and started coming out the air filter. Now that I think of it, that wouldn't really put smoke out the intake manifold gasket would it! Do that again and open the throttle?

06-26-2022, 01:40 PM	#14
intothelabyrinth Board Member Join Date: Mar 2012 Location: Bowling Green, KY	Im gonna smoke test again. Any tips on where to plumb the smoke in?

06-26-2022, 02:00 PM	#15
ZVOLV <Master Tech> Join Date: Nov 2002 Location: California	You could cap off the intake hose at the MAF, crack the throttle and try again. Maybe something will show up that didn't last time. Another trick is spraying around with brake cleaner at idle and seeing if you can get the engine to stumble. On modern cars, I spray around with brake cleaner and monitor fuel trims with a scan tool to find air leaks. It works well.

06-26-2022, 04:13 PM	#16
intothelabyrinth Board Member Join Date: Mar 2012 Location: Bowling Green, KY	Pulled the plugs and they all looked fine and the same. Tested compression dry and got Cyl 1 143 Cyl 2 150 Cyl 3 150 Cyl 4 146 Changed plugs to bpr7es and put on new wires. No charges. Leakdown test next. I'm really starting to suspect a burned exhaust valve. This had to have happened before I got the car because the bouncing vacuum deal was there from the moment I put the boost gauge on, which was before the +t was used at all. Maybe the po rode around with a vacuum leak forever?