First, let me confess that I'm in the 960 forum with a problem on my 98 S90 (B6304) - Hope that doesn't get me promptly thrown out! This nightmare of a repair began with P0300 code with misfiring being reported on cylinders 1 & 6. After reading around the forum decided to install a new intake manifold as suggested by some others.

Took the easy route and pulled the intake back from the block just far enough to get the new gasket fitted and snugged everything back up nicely. I then decided to give the throttle body a nice soaking bath in carb cleaner - after removing the throttle position sensor of course. Got everything back in - and thought we were ready to call it a day.

The car started without significant grumbling as I recall - but I killed it quickly when I realized I hadn't reconnected the return line on the backside of the fuel pressure regulator. Lost about a quart of fuel but could've burned the house down and didn't!)

With everything back together and double-checked I started the engine again and here's what I've got:

No codes on the OBDII except a P0301 (maybe the gasket wasn't the problem after all). The car idles very irregularly - but it will idle. But slowly applying pressure to the accel pedal and it dies instantly.

Suspected a bad TPS, even though it checked out on the bench. Have just replaced that piece with new OEM and, whereas the idle is a bit smoother, movement of the throttle plate still causes the engine to die. I can coax it up to 2000-4000RPM and it runs very smoothly albeit under no load. But getting through the 700-1000RPM range is ugly at best.

I've checked every fitting on the intake for leaks (none), checked vacuum at all control lines (in range) The only connection I can not identify is the EGR - anyone know where that thing is??

Despite a little shake at idle, the car ran smoothly/powerfully before this repair - it has been burning small amount of oil for some time now. Just can't figure out what I've done to immobilize it! Any ideas out there?

 

So now it just idles bad now?
I would also check compression.

 

The idle regulation is not great but the key symptom is that the thing just suffocates when coming through the idle band - a fatal hesitation that simply wasn't there before this repair. I'll try to get hands on a new compression tester - mine won't make the trip down through the top of the head.

Two things are rattling around in my head - where is the EGR port and how does the ECU calibrate itself to a new TPS. Still looking for answers on those.

 

The car should have an air pump and not EGR.
The computer just reads the position of the sensor. If you install a new one it just sees it.

 

Ok on the air pump, just didn't cross my mind that it replaces EGR function - but fresh air in the exhaust lowers temp the same way as exhaust gases in the combustion chamber - without all of the mess of the latter.

S90 is first Volvo I've had outside of the 200 family ('84 245, '92 244, '93 245) which all use throttle plate switch. I was just thinking that the voltage reading out of the S90 (analog) TPS between throttle "closed" and "just cracking open" has got to be fairly small (maybe 1-2degrees out of 90?) I was just hoping maybe that there was a calibration step I was missing.

Thanks for the feedback - and any more is welcome. I'll get the plugs out this weekend and see how the compression looks.

 

The bad news is in - compression readings this morning look like this:
30# - 210# - 230# - 175# - 220# - 220#

30psi - that would explain the miss on #1 wouldn't it?

Still puzzled why this thing turned into a complete heap on this repair - but, at this point, it probably doesn't matter. I don't think (if I could get it back into the shape is was before) that it could pass emissions tests.

The OBDII reader shows 0.000v on the #2 sensor - I think that is on the downstream side of the catalytic convertor. All the plugs indicated a very rich mix, perhaps that eventually took that sensor out. Not sure the dead sensor could create the symptoms I'm seeing but I know very little about the Motronic system, when it is running open-loop, etc.

Thanks for the feedback - your recommendation to do the compression check has, at least, shortened the mental agony. Now time for the financial pain to start.

Regards, Charlie

 

I put a tablespoon or two of pump oil down #1 and restested, still getting 30psi. That point to a stuck valve or lifter, I'm assuming the b6304 uses hydraulic lifters.

Is this thing dead, or begging for some snake oil -- MMO, restore, ??

 

I will bet you have a burnt valve!

 

Anyway to conclude that without a teardown?

 

Sorry but no the compression test pretty much confirmed it already.

 

Some progress, a miracle cocktail - and yet the problem remains. I tried an oil cocktail that I found on a non-Volvo board (MMO + Restore + Carb Cleaner Spray). I added the first two to the crankcase. Then I drilled a small hole in the rubber intake boot at #1 started the car and let it idle until warm then I emptied the carb cleaner into the cylinder. After a couple minutes of this, engine smoothed out and now I've got compression (~180#) on #1. That's the good news!

The thing idles much more smoothly now - very smooth and no P0301 codes. But, the instant I come off of idle it just dies. Also replaced the fuel filter thinking I may have blocked it during this repair when I ran the tank nearly dry. To no avail.

I'm still cranked about this new TPS and how the ECU knows what voltage (exactly) represents the idle condition?? I know from the throttle switches on my 240s that the ECU has to know precisely when the plate is opening so that it can beef up the mixture to meet the incoming rush of air. Have even found many references to TPS calibration/reset on Buehl motorcycles that use a Motronic ECU of some sort. BUt nothing on MFI 1.8, Volvo, etc. and you've told me it just works. I just can't explain what I'm seeing.

So I'm at a point where the cylinders look reasonably good -- but still can't get it out of the garage.

 

I'm beginning to believe I'm chasing the wrong problem! So I'm going to just get over this whole TPS calibration thing. What I realized is that, although I can coax the thing into running in the 2k-4kRPM range - I CAN'T HOLD IT THERE. It just starves out and drops to zero! I'm guessing maybe that the pressure in the fuel rail is below the line. I did a flow test the other night but I couldn't conclude much with the pump only running on the first couple of seconds after the switch.

I mentioned earlier that I replaced the fuel filter last night b/c I had run the thing nearly dry earlier and was thinking I might have blocked the thing up. First things first right? That was a 15min job - but it's no better now. I'm thinking that the screen on the in-tank pump might be trashed. It looks like I've only got the in-tank pump on this model (separate post in the S90 forum).

That's my theory at this point - but the in-tank pump looks like its going to be a pain to get out. I may just have to get a fuel pressure gauge to convince myself that I'm going in there!

 

I would test with a guage first.

 

Ok, this vehicle is officially retired from service. In a fit of irrationality following many days of 4hours sleep - there's a new T***** in the driveway and the S90 is now mine to give away or fix. Thanks for the help, I'm moving over to the S90 forum looking for tips on locating a good rebuilt cylinder head, etc. Charlie