´96 850 engine struggles

Teddy1975 · Post by **Teddy1975** » 27 Jun 2017, 07:11

My 850 with engine B5202FS, 10 valve N/A, 205K miles, is now really struggling under accelleration.

When driving and trying to get past 3200 RPM, the engine stalls like it doesn't get enough fuel, but I can rev it beyond that if I put it in neutral.

I've begun noticing a smell of burnt oil when I start the engine, but I haven't seen any blue/black smoke from the tail pipe.

Can anyone please point me to where I should begin my troubleshooting?

Thanks,
Teddy

Post by **hausmeister** » 27 Jun 2017, 09:17

I have no definite idea for your problem, but I also have a 2l na and these are my experiences:
check vacuum lines (improves performance a bit)
Make sure Iginition is in good condition
maybe check the Air intake temp sesor. This one caused me massive problems because it did not set an error for a long time. That was the first real problem with the engine I had in the 10 years I have had it.
If the car does not have a code set then it is trial and error. Also the Siemens Fenix ecu is not very cooperative with most readers...

Teddy1975 · Post by **Teddy1975** » 27 Jun 2017, 14:17

Thanks hausmeister.

I'll see if I can coerce any Fenix codes out of my home-made flasher tomorrow.

I had a brief look at the air intake temp sensor and the connections are quite corroded and I can see a bit of dirt inside the housing. I have to postpone until tomorrow to attempt to clean it properly.

Last time one of the vac lines acted up, the idle surged much higher than the 850 rpm it settles right down to after cranking now. I'll inspect them to see if there's an elbow gone bad again.

The ignition may be the culprit, but I need to read up on how to test it.

Teddy1975 · Post by **Teddy1975** » 28 Jun 2017, 13:04

There were no codes set, just blinked out the 1-1-1 pattern.

Air intake temp sensor measured 2.4 ohms at room temperature and dropped when heated with a hairdryer to 1 ohm. I don't know the range it's supposed to operate within, but it behaves like I'd expect it to.

It sort of feels like the engine only runs on four cylinders, the lack of power under load is quite severe.

I'll go buy a compression tester on Friday. If for nothing else, just a peace of mind knowing it isn't due to worn piston rings or worse. I'll pick up a fuel pressure tester too.

/Teddy

Post by **rspi** » 29 Jun 2017, 19:29

Probably a weak fuel pump.

Teddy1975 · Post by **Teddy1975** » 30 Jun 2017, 08:40

Hello Robert, thanks for your help.

I went and got a new fuel pump today, although not a Bosch, just a cheap(er) locally sourced one.

The new fuel pump and a fresh set of Volvo plugs has made the engine regain about 10% of the lost power.

The old spark plugs with about 500 miles on them look like this:

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To me they look kind of worn for such a little distance.

I tried replacing the fuel pump relay but the new non-KAE one just made it a whole lot worse. Idling went from 400 up to 1600 RPM and the instant I put my foot on the pedal the engine died. I've driven home from the spare parts center by-passing the fuel relay. On the trip home, I noticed the rev counter drop every so often, something I haven't seen before. It's only about 100 rpm or less and just for a very brief moment, but it is noticable.

At times I drive with WOT, engine won't go past 3500 RPM, but pulls a little stronger now.
I haven't yet replaced the fuel filter, will have to wait until Sunday for that as it'll rain non-stop until then.

/Teddy

Teddy1975 · Post by **Teddy1975** » 02 Jul 2017, 09:09

Hi again.

Hausmeister, I think you're right about the IAT sensor being faulty. I found this after a lot of searching:

INTAKE AIR TEMPERATURE SENSOR RESISTANCE TABLE
Temperature - F (C) Ohms
-4 (-20) .................................. 15,000
32 (0) ...................................... 5800
68 (20) ..................................... 2500
176 (80) ..................................... 330
212 (100) .................................... 160

The ohm range on my IAT is 1-2.4 ohms, clearly not within spec range.

Will check further.

Thanks a bunch for your time,
Teddy

Teddy1975 · Post by **Teddy1975** » 02 Jul 2017, 09:45

Blinked out a code 3-4-3. Guess I'll pick up a new KAE fuel pump relay as well as an IAT sensor and see where that'll take me.

Teddy1975 · Post by **Teddy1975** » 03 Jul 2017, 12:24

Saga continues, wasn't a bad fuel pump, nor relay, nor the IAT. Though I consider the relay and pump preventive maintenance and the IAT needed replacement anyway.

No, the culprit is unfortunately this:

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Teddy1975 · Post by **Teddy1975** » 08 Jul 2017, 15:53

Update:

I managed to procure some stick welding rods for cast-iron and welded the cracks in the manifold.
I'm not a professional welder, certainly wouldn't get through any inspections of my welds, but they all solid with full penetration. More importantly, no new cracks formed during or after welding.

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Put it in back in the car and thought my struggles were of the past. No, they're not

Had a thorough test of all vac lines in the engine bay, they seem solid, apart from the one going from intake manifold to flametrap.

The vac line from the fuel pressure regulater at the rail doesn't smell of gas, and the EGR valve has plenty of vacuum too. Thought I'd give the TPS a bit of trouble shooting too, since there's no problems at idling, it only gets noticeable when reving it, to the point where'll it'll almost choke itself to death at 3000 rpm. However ohm read out was fine and the voltage within Volvo spec.
Funny thing I noticed it the air valve in the airbox that switches from cold and pre-heated rate is rpm spefic. The higher RPMs the more it opens to let in cool air from the front in.
Tomorrow, just for the heck of it, I'll replace the fuel filter. I have to cut out the retaining bolt as it rusted in place and I don't feel comfortable putting any kind of heat near the fuel lines.

Something else I was thinking it might be, was the camshaft position sensor. Can a failed one caused any of the symptoms I'm expriencing?: Strong and solid crank, will fire right up after turning the key, the idle gets up to about 1000 RPM then settles right down to ~850 rpm with no jittering at all.

Must admit I'm seriously fed up with the car as it is right now, I can't afford feeding it new parts all the time hoping it'll fix the, but can't afford to just walk away from it either. Fortunately I'm on vacation and won't need to drive the car daily until August.

/Teddy