Hi All,

I'm still having issues with my 850. It wasn't fixed, or it came back. I'm looking for any further suggestions.

First, here is the original thread. (I tried to reply, but it was read-only.)
href="http://www.brickboard.com/AWD/volvo/1427501/850/intermittent_stumbleroughstall.html">Intermittent stumble/rough/stall

To summarize, I have a '95 850 Turbo sedan, and I'll be driving along just fine, and it will start running rough and lose power, run that way for 1 to 5 seconds, then continue on just fine.

If I'm driving down the freeway, constant speed, flat road, the car will start to do this, and I feel it surging, slowing down. The tachometer is rock steady, so I'm pretty sure it's not on the primary ignition side.

It was giving me 1-2-1 error codes, which is the MAF sensor. I changed that, and it seems to have not fixed it. In retrospect, that may have been a red herring. Most of the time when it stumbles, it does not set any codes. It's only if I'm at low speed and the engine stumbles to the point that it does (or almost) stops running completely after 10+ seconds of hiccuping around that it sets the code. If it's shorter, or at a higher engine speed, it does not set a code.

Seems to make no difference if tank is full or empty.

Makes no difference if it's hot or cold (or wet or dry) outside.

Yesterday, when it was stumbling at idle, I opened the throttle wide, (pedal to the floor,) and it made no difference. It kept stumbling, until it stopped stumbling and behaved; I parked. When I subsequently started it again (10+ hours later) it stumbled a little bit, then after less than a mile, it stopped stumbling and was fine.

I changed the spark plugs. They had 30,000 miles on them - Bosch Platinum. All were identical, with a very light, light grey color. Put in a set of Champion copper. No change, same occasional behavior.

The behavior is very binary - either it's running fine or it's stumbling, like flipping a switch.

I'm suspecting an intermittent electrical issue, but can't figure out where.

If it was the fuel pump, it would just cut out and stop. If it was a partial blockage, it would tend to be worse at speed. (or would it?) Yes, it would. Even though the pump is at constant volume, the pressure regulator would end up closing a little more to maintain pressure, and it should idle fine, just have issues at WOT. I also don't think it would be intermittent like this - it might be intermittent run or not-run, but not intermittent stumbling. Wish I could monitor fuel pressure while driving.

Thus, I'm trying to think of what sensor might be going open circuit to cause this behavior, but not set a trouble code.

It also doesn't seem to be related to movement. Going over bumps or a bumpy road does not trigger or fix this. Nor cornering vs. straight. It will, however, start or stop while driving straight and flat down the freeway.

It's not a cam or a timing belt issue - that wouldn't be intermittent.

Vacuum leak wouldn't be intermittent - it would tend to make it run badly at idle, and be fine at speed.


Any suggestions?

Thanks in advance!

Roger

'95 854T 235k miles
'87 245 M47 278k miles

Following up for the archives.

I replaced the Turbo Control Valve, TCV, located on the air filter, and that seems to have fixed it. I have driven ~1700 miles, and the rough running has not reocurred.

I'm still working to understand exactly how the TCV works. I understand that it allows the ECU control the wastegate, but I'm not sure of the exact mechanism. I have received contradictory information (anecdotal) that it either operates on/off, or modulates via Pulse Width Modulation (PWM). Plus, it either applies intake manifold pressure or atmospheric (or slightly lower, just downstream of the AMM) to the wastegate operator. If the normal wastegate operation is to allow high intake manifold pressure to operate the actuator, I don't understand how switching that to a slight vacuum will reduce boost. It seems like it ought to keep the boost high.

Anyway, I replaced it on an anecdotal report that this valve can produce the symptoms I described, and while I don't understand the mechanism, the problem has not reocurred, so I'm not complaining.

Thank you all for your assistance!

Roger
'95 854T 251k miles
'87 245 297k miles M47 (about to get new clutch)
'93 945T 211k miles (new to me)
et al.

Maybe check the MAS plug connector pins they have been known to get intermittant. How's your intake manifold vacuum reading? Any rattling from the catalytic converter? Maybe it's getting plugged intermittantly.

I'll check them.

A little doubtful on both, as the issue comes and goes with zero correlation to engine movement (cornering, acceleration, deceleration, bumps / rough road). Indeed, I can be driving down a flat, level road, constant speed, and have it start to stumble, stumble for 1 to 10 seconds, then pick up and run as if nothing happened. If it were some sort of intermittent electrical issue, or cat with broken guts, I'd expect more of a correlation to significant movement. Still, I'll check.

Thanks!

Roger

Might be some bad connection in the fuse or relay panel or ignition switch?

Next suggestion is to clean the throttle body and make sure that the vacuum tree has no leaks. While there, clean the idle air control with TB cleaner.

While there, check the vacuum line from the fuel pressure regulator to make sure it doesn't have any gasoline in it.

Klaus

Thanks Klaus. I had most of that apart not too long ago (replaced knock sensors), and cleaned TB and replaced any suspect vacuum connections at that time. Still, worth a check, so I inspected and all looked good.

I'll check for gasoline in the line to the FPR. Is that symptomatic of a leaking FPR diaphragm?

Working to find a gauge suitable for checking fuel pressure.

Roger

PS - just pondering the timing of events... I replaced knock sensors in April, which required removing intake manifold. Car started having present issues (1st time) at end of June. Thus, about 8 to 9 weeks later. So if I screwed something up when I was doing the knock sensors, it took ~8 weeks to manifest itself. I'll inspect closer, I think.

Unless one of the manifold bolts worked its way loose, there shouldn't be a problem. You could retorque them.

Check your turbo pressure gauge when driving, it is a vacuum gauge and should go far to the left when letting up on the gas indicating good vacuum.

I had a problem fitting a Ford fuel pressure gauge on my 850, the engine support gets in the way when you hook it up to the schrader valve.

The nest time the engine dies, flip the rear seat forward so you can easily hear the fuel pump. Turn the cabin blower and radio off.

The fuel filter is cheap to replace.

Klaus

Vacuum gauge indicates good vacuum.

Fuel Pressure test was was pretty good. Wasn't exactly on 43.5, was reading 46, but may have been gauge error.

Even with the engine off, fuel pump running (had pressure, heard fuel flowing through fuel rail,) I couldn't hear the fuel pump. Head in trunk, opened gas cap and listened at the fuel filler, couldn't hear anything.

Having lived through the "240 Fuel Pump Relay" issue, I disassembled the fuel pump relay and inspected. I observed the 850 is happily more robust - the high current leg doesn't go through the PC board trace any more, so the main 240 failure mode is gone. Anyway, one of the coil leads looked potentially questionable, so I touched it up with a soldering iron. Not necessarily the problem, but I figured it wouldn't hurt.

Roger

The 850 fuel pump relay still has its own share of problems, like the solder joints at the connectors. But when the relay fails, the car will stall and not just stumble.

The higher fuel pressure could also be related to a lower vacuum pressure. At zero or positive pressure, the regulator is supposed to increase pressure by about 4 lbs. Just check the vacuum line for the presence of gasoline.

The fuel pump can only be heard when you turn the key to pos II, before start. Unless you have a non-oem pump which can be noisy.

So lets assume you have a good pump and no vacuum leaks. The throttle body is clean, the IAC is clean, the MAF is clean, the fuel filter is good. Is the rotor or cap in good condition? Are the lead wires less than 10 years old and not arcing? You plugs are gapped at .028 and clean. You have blown the carbon out of the cylinders recently. And I am out of ideas....

Klaus

Klaus,

Thanks for all your help. I'm not going to worry if my fuel pump is too quiet - it's delivering fuel! 8-)

Even if the fuel pressure is 2.5# high, I don't think it's enough to cause this. I've heard anecodtal reports of people not having issues until it gets up to 70+, or down to 20#. I'm not sure what the published tolerance is for fuel pressure, (if published,) but 43.5 is conveniently right on 3.0 bar, and if it was really 3.0 bar +/- .25 bar I'm within tolerance. (I have no idea what the tolerance really is - just noting that I'm not that far out.)

Cap, rotor, and wires were all new Jan '09, at 208k, so all have 20 months and 28k miles on them. Spark plugs were also new at that time, but replaced last week as part of the troubleshooting process. Plugs were gapped at .028, came out a little worn, light grey. Replaced with new, no change.

There's one more possible vacuum leak I'm going to chase down - I hear a noise at (behind) the fuel rail that may be fuel flowing in the fuel rail fittings, or may be a leak. (I can't recall what the device is under the intake manifold - it's got vacuum lines going to the turbo wastegate area, which have been replaced...) Vacuum tree is good, throttle body was cleaned recently...

Can you suggest a good solvent for cleaning throttle body? I recall it was difficult to get it spotless, and I may attempt again.

I'm out of ideas too. I'll keep running it - eventually something may fail completely, at which point it's easier to fix.

Thanks again for your help!

Roger

Oh, I was looking through documentation for the s80 today and I noticed the 99 had a tolerance of 1 kPa (.01bar). Granted the 850 is a bit older, but I don't think it should be less accurate. Your gauge read that you were off by 17 kPa which is a pretty big difference.. That leaves me with four possibilities. Your FPR damaged (likely), you have crap in the line (very unlikely), your gauge is incorrect (unlikely b/c you can calibrate and its new..), and a vacuum leak (likely). You've searched almost everywhere for the vacuum leak. The only real place you have left is the intake manifold and the breather system. If you have a P'n'P yard near by get the FPR and try it. It shouldn't run you more than $10 and it will leave you with just a vacuum leak as the 99% cause..

The gauge was a litte out of calibration. (It wasn't new - it was one I put together using fittings etc. I had around.) I put a different (much higher quality) gauge into the setup, and it read 44.0 psi. Still very slightly high, but I'm sure it's not the cause of my issues.

The thing I'm thinking of underneath the intake manifold is the oil trap. I see per the manual that it doesn't have any vacuum connections to it. The one vacuum connection I was thinking of is the one that's in the dual pipe with the oil trap line that goes back to by the turbocharger. The other end of that vacuum connection is the one Klaus mentioned behind the power steering pump. That connection looks good, and is a relatively new elbow.

I will follow up with a good vacuum leak test. Not tonight - it's late, and I'm already in the doghouse because I spilled a bit of gas re-checking the FPR, and the smell got in the house. 8-( I think I'll go for the propane test, outside (when it's not raining). And yes, when I put it all back together after doing the knock sensors, I used the cheap intake manifold gasket. (Didn't think so at the time, but now...) So I'll be sniffing all around there, and see what I can come up with.

Roger

There are only a few things under the intake manifold: knock sensors, oil separator, and starter. Only the oil separator can leak air at the engine block hole or the 2 vacuum lines.

Before taking the manifold off, again, try some butane to look for a leak. It is possible that the manifold gasket is leaking underneath. If you put on one of those gawd awful gaskets from FCP, that could easily be the problem.

Klaus

The only thing at the fuel rail is the pressure regulator and the injectors. Could it be a bad injector with a poor spray pattern? Just pull the stone shield forward to remove it so that you get a better look at the injectors.

Check the connection of the bandit vacuum line behind the PS pump. Don't want that to get loose.

Klaus

Right behind the rail as in where the FPR is? A slight leak there and you've solved it!

How much hose do you have? Can you do the test while driving or it not possible to run the gauge to the drivers seat. While driving the car the pressure should be between 30.4 and 55 psi. At constant load the fuel pressure should be constant, however if you're accelerating or engine braking it will change.

While 46 isn't that far from what it should be, it is still high. The NA engine should never get that reading (it should be between 30.4 and 45 psi). Being metric Volvo differentiates between 300 and 310 kPa which leads me to believe tolerance is at most .1 bar if not less...

Just to recap, have you pulled off the rail and looked on the underside at the FPR and the hose going to it? The elbow right there likes to fail...

The elbow at the fuel pressure regulator is new. I replaced that proactively when I had the intake manifold off for the knock sensors. I also replace the one that goes in the left side of the intake manifold, and any others that were feeling "soft".

What I think I hear is coming from underneath the intake manifold. I've got to get in there and look more. (Might have to pull the manifold off again.)

I have a different gauge I can use to check calibration of the test gauge to confirm the reading.

If I can't find anything else, I may end up just replacing the FPR, although I really hate the "replace parts until the problem goes away" approach.

Interesting note: If the pressure is slightly high, that would cause it to run slightly rich. However, I came across a post from Klaus (different thread) that suggested light grey spark plugs indicated running lean. Not sure how to interpret this. Ah well.

I'll find it eventually. Thanks for the input!

Roger

I wonder if your car runs lean on occasion because the car assumes fuel pressure is correct so it changes fuel injection times to make it right, but then pressure drops. I wonder if you're running with rich/lean alternations every now and then just to screw with your head!

A driving pressure test would be helpful to see exactly where your fuel is at when its stumbling. Otherwise I'd say check when you turn it on, check after driving a min or two, and check after 10-15 minutes of driving. Also, get your helper to sit on the brake and put it into gear and see what the pressure changes. It should slightly change under load, and though being on the brake at idle isn't much load you should see it with the gauge..


Underneath the manifold as in from the breather system? I bet you'd love to find out that little hose that connects to the engine behind the oil separator is leaky.. Nothing like tons of extra work...

I just had a similar issue with my 96.

Intermittent loss of power, no codes.

Hooked up a fuel pressure gauge and pressure was at about 20psi when it should have been in the high 40s.

Replaced the pump and gained 50HP!!!

So, I would not assume that a failed fuel pump is a complete failure, or no failure at all. As was in my case, it can be a partial failure.

I agree. Sounds like a fuel pump dying a slow death, I would first check the fuel pressure regulator, just to make sure it is ok.

Fuel pumps play strange tricks when they start to die. And fuel delivery failure is one of the few things that do not set a code. Perhaps the 121 MAF code you got, may have been caused by engine moving more than normal due to stumbling. Sometimes just a smmall movement of the connector will interrupt the signal.

Do you have any idea on the mileage you have on this fuel pump?

Thanks for the input!

The fuel pump was replaced in 6/2005 at 152k miles. It's now at 236k miles, so the current pump has 84k in 5 years.

Last time it died, it was pretty binary. Driving along, coughed and sputtered a little, then a dashboard full of lights, and coast to the side of the road. Replacement pump was purchased via internet, came in a Volvo box if I recall correctly, so an OEM part.

Working to find a fuel pressure gauge to test that. We'll see what it shows. Thanks!

Roger

Just to let you know, on my '96, the original fuel pump died at about 150,000, two years ago. It was a binary failure. Replaced it with an insert pump--don't remember if it was OEM or not. I do remember that it was not the same as the original insert; different diameter, if I remember correctly. Had to modify the coil spring, if I remember correctly. Regardless, it resolved my orignial problem.

This second fuel pump has now died at 175,000 (only two years old) with a low pressure failure. Before I replaced this pump, I took out the old pump and checked everything in it from top to bottom. Did not like the way the electrical connections were being strained, so I completely re-did that. When I returned it to the tank, the original problem persisted, so this time I replaced it with the whole, Volvo, $375 pump assembly.

Not saying that low fuel pressure is the reason for your problem, but certainly an area to check.

Thanks Ken, good to know.

I'm in the process of getting a fuel pressure gauge setup together - should be checking that tonight or tomorrow. I'll post what I find.

With your low pressure, what were the symptoms and test results? Specifically, how did you conclude it was the pump vs. obstruction / clogged fuel filter vs. pressure regulator? If I recall correctly, the pump is constant volume. Thus, if the pump is failing, you would pinch the return line and deadhead the pump (briefly), expecting the pressure to rise to a deadhead pressure. Correct? Then if the pressure comes up to the proper value, it's either an obstruction/clogged filter, or the regulator. You then do a "total volume" fuel test; if it passes the volume test then it's not an obstruction, and by default is the regulator. Am I correct?

Roger

You are correct, though considering you replaced the filter its unlikely you have a clog in the line to the engine. You can disconnect the return line and blow through it if you want. You would have high pressure if the line were clogged at this end though, so you're just blowing for fun...

When you check it should be 300kPa (43.5 psi). If its low you squeeze the return line but DO NOT let it exceed 600kPa (87 psi) or you'll be in a world of hurt...

If you deadhead it and the pressure does not increase, first check the filter gauze at the pump, and if that's not crap, replace the pump.

If it does rise, the problems is the regulator.


If you have to replace the pump, get OEM, don't go aftermarket. You can probably pull one from a pick-n-pull quite easily that will last you 2x as long as an aftermarket would, and for less than $20 I'd try 3 before I bought a new OEM one.. (also, at PnP yards, you can return for credit, so you only have to buy the one, and try two others free...) I believe all 850/s70/c70s up till 2002 used the same pump so it shouldn't be that hard to locate a donor.

Fuel pressure check seems ok.

Engine off, relay jumpered, read ~46 psi. Not sure of the gauge calibration, so it could be the gauge off by 2.5 psi, not the fuel pressure. Generally in conformance to spec.

I pinched off the return line, and the pressure went up quickly. Released before it exceeded 86. (It was heading to shoot right past.)

Kept the gauge on and started the engine; fuel pressure dropped to ~37 psi. Pulled off the vacuum hose from the vacuum tree, and the fuel pressure jumped right back up to 46psi. Put hose back on, and it dropped again to 37psi. Also of note, no fuel came out of the vacuum line to the FPR when it was disconnected while running.

Thus, while I did not get an exact gauge reading, I am concluding that the fuel pump, fuel filter, and fuel pressure regulator are generally working and not the source of the problem.

Roger

'96 and on are a bit different, not having the same pressure regulator, return line arrangement found on the earlier models, so I can't speak to some of your questions.

Symptoms were, poor acceleration--if you floored it, there was very little power. It seemed to be better if I just drove, feathering the accelerator.

When the power loss first started, I realized that I had not changed the filter in about 75,000 miles, so that was my first action. The new filter did not improve the situation, which is when I pulled out the fuel pressure gauge. With the low pressure indicated, I pulled the pump and tried to discern any issues. Was not happy with tension on the wires, so I rewired the unit with a bit more wire. Put it back and no real change.

Was not happy with the Harbor Freight fuel pressure gauge, so I found a really nice 4", oil-filled, 60PSI gauge at a surplus store in the area and re-checked everything. The gauge is really nice and I was much more confident of its readings.

I did not check for obstructions and just decided to step up to the new pump, which ended up being the problem.

Hi Ken,

Thanks, that makes sense. Reduced high power performance because the fuel flow needs exceeded what the failing pump would deliver. And you changed the fuel filter first, with no effect.

If one had a fuel pressure gauge you could watch while driving, I am guessing that your pressure dropped significantly lower when you called for more power. (In a properly functioning system, it should remain the same, with the fuel pump able to supply more fuel than needed, and the pressure regulator modulating return flow as needed to keep the pressure correct.)

Roger