Two Sensors Die at Once? 98 v70 T5

[WagonLagan]

As a test (it will throw a code), disconnect the MAF plug with the engine off and see if idle stabilizes.

Just for S&G have you tried running it with the MAF disconnected?

Thanks guys, that clarifies my next action.

Also, I realized that if disconnecting the baro sensor didn't change anything, replacing it won't either. Duh.

I think you need a live scanner hooked up to see what sensors are reading what.

I have a scanner that feeds live data to my phone, but I honestly have no idea what I'm looking at. Barely know how to use the thing as I just got it. I peeked at the O2 sensor readout and saw some red X's, but I don't know what that means, lol. Picture included.

Screenshot_20170714-184216.png (118.26 KiB) Viewed 1148 times

[abscate]

We do need to find someone who can find the present code, clear it and monitor.

Can you monitor the short term fuel trim on the warm engine

At idle...

At 2500 rpm

And report the graphs with a screen shot?

[WagonLagan]

So this is interesting.

Unplugged the MAF, no change, plugged back in.

Unplugged the IAC (Idle Air Control valve), stable idle.

Plugged in the IAC, stable idle.

Could the IAC be failing? I recall someone mentioned about the idle sequence being a closed loop and vulnerable to even small variance?


Also, in case it helps, is it abnormal for exhaust to smell significantly of gasoline?

EDIT:
This person had surprisingly similar issues to mine, and their issue was the IAC apparently.
viewtopic.php?f=1&t=52541

[WagonLagan]

Cleaned the IAC. It didn't seem that bad to me, but it might have been moving easier afterwords.

Took it around the block and it shuddered a little, but not nearly as bad. Going to try taking it to work and back later today.

Will report back.

[mrbrian200]

No it's not normal to smell gasoline in the exhaust. It should smell almost like nothing- damp and slightly 'musty'. That sort of supports my theory that the white smoke you saw resulted from massive amounts of fuel being fed to it.

The IAC could cause sputtering and a rich condition at idle. But if it continues to sputter and run rich while accelerating there's something else going on.
We won't assume the oxygen sensor is bad just yet--if the engine is flooding out with gas the O2s may be having trouble getting to temperature in which case it would read low. Excess fuel has a cooling effect.
Does anyone know if this older motronic system will catch if/when the O2s internal heater element goes out?

[sleddriver]

Whelp... That didn't work. If anything it seems to have gotten worse, lol.

And, interestingly... the CEL comes on, but there's no codes according to my OBDScanner.

During the smoke test, I couldn't see any areas of significant smoke leakage, apart from the one that had fallen off. However, given the fact that it got WORSE after replacing that vacuum hose, I find it unlikely that a damaged vacuum hose is the root cause here.

If it helps anyone diagnose, before this happened, I did have rare, occasional stutter for months, but never, ever this bad. Just an occasional dip, not even once a day. I just chalked it up to 250k miles.

Could electrical issues with the wires to the TPS cause this? If I have to take it to the Indie, I'd at least like to give them a place to start looking.

First, smoking the intake manifold, engine & gas tank takes a bit of time as the whole system needs time to fill up with smoke. You may have to bag the exhaust should a valve be open allowing smoke to escape. You should remove the gas cap until smoke comes out. Also the EVAP SHUT-OFF valve vent needs plugging. Only when all is sufficiently pressurized, will you get a thorough smoke test.

Second, you recently mentioned replacing the PCV system. Did you do the work? Was the rubber elbow at the belt-end of the engine replaced while the manifold was off? Was everything hooked up properly at the turbo inlet? Have you verified that the fat pipe connecting the oil sep box to the intake has not cracked? Even if you used a Volvo part, this rigid pipe is known to crack. Been there, done that. Robert has a video on replacing this.

He also has a video on intake manifold leaks to watch out for when doing the PCV system. Some ding/mess up the gasket and it doesn't seal well. All IM bolts need to be torqued to spec.

Third, you need to make a checklist to verify each & every vacuum hose, elbow & fitting to ensure their integrity. Don't assume...VERIFY! Turbo motors have LOTS OF VACUUM HOSES and TWO MAIN CHECK VALVES. All have two ends. Both ends need checking!

[mrbrian200]

Disconnect the vacuum hose at the fuel pressure regulator. You don't have fuel shooting out of there do you?

1. Plug the vacuum hose going to the engine with a bolt or something that can't get sucked in.
2. Run a temporary hose from the vacuum connection of the pressure regulator to a bucket or anywhere if gas shoots out it doesn't land on the engine and start a fire.
3. Start engine and observe. Nothing should come out of there. Not so much as a drop or even fumes.

I had this fail on a Taurus once quite a few years ago. It also took on an intermittent nature. It appeared to run fine most of the time then would just run terrible for anywhere from a few seconds to minutes then recover. Sometimes if you stopped/restarted the engine it would run normally again. So long ago I forgot about this. Without the vehicle in front of me it's easy to forget these older cars used these things and it's a checklist item if AFR is running rich.

Costs $0 to check. And could fit your symptoms. According to what I see your fuel pressure regulator looks like this:

FPR.JPG (11.29 KiB) Viewed 1078 times

[jblackburn]

Disconnect the vacuum hose at the fuel pressure regulator. You don't have fuel shooting out of there do you?

1. Plug the vacuum hose going to the engine with a bolt or something that can't get sucked in.
2. Run a temporary hose from the vacuum connection of the pressure regulator to a bucket or anywhere if gas shoots out it doesn't land on the engine and start a fire.
3. Start engine and observe. Nothing should come out of there. Not so much as a drop or even fumes.

I had this fail on a Taurus once quite a few years ago. It also took on an intermittent nature. It appeared to run fine most of the time then would just run terrible for anywhere from a few seconds to minutes then recover. Sometimes if you stopped/restarted the engine it would run normally again. So long ago I forgot about this. Without the vehicle in front of me it's easy to forget these older cars used these things and it's a checklist item if AFR is running rich.

Costs $0 to check. And could fit your symptoms. According to what I see your fuel pressure regulator looks like this:FPR.JPG

This would be my next suspect. They have been known to chug fuel into the IM when the regulator fails

[mrbrian200]

This would be my next suspect. They have been known to chug fuel into the IM when the regulator fails

If the car were in front of me I would have caught right away before even plugging in a diag tool that the exhaust smelled of raw gas. Opening the hood I would have seen and recognized that vacuum modulated regulator and probably been checked within the first 5 minutes. Because unplugging that vacuum line is all you need to do and it takes seconds. And they're almost always right up top on the fuel rail.

Some things which would be quite obvious in person often get overlooked over the internet.
We need to come up with a ten or fifteen point multiple choice checklist for people without a diag tool/live data that we can point people to so they can make a somewhat more 'scientific' assessment of run quality that makes sure major points aren't overlooked ...Things like what does the exhaust smell like, if there is visible smoke what color does it appear?...Idle quality smooth or rough/uneven?...hard acceleration smooth or rough/uneven/no power? ... Has a check engine or any other warning indicator been lit, and if so for how long/approximately how many miles? Pull the oil dispstick- how does the oil appear? ...inspect the bottom side of the oil filler cap, multiple choice- A. Clean shiny metal or plastic B. black crusty deposits C. soft milky film...
Simply nailing down the exhaust 'quality' with a couple multiple choice questions is as helpful as about anything when you're lacking diagnostic data. When I'm buying a used car I always show up unannounced, start the car and immediately fly back to the rear exhaust and inspect/smell it--including cupping my hand an inch over the pipe to collect condensation and will hold that right up to my nose for a 'close sniff assessment'. Exhaust quality on a cold start is very telling of overall condition and/or if there's something wrong. After it's warmed up and driven a few miles I'll check the exhaust again.

[jblackburn]

I believe the FPR is just inside the right axle on a 98. Follow fuel lines and you'll find it easily.

The thing in between cyls 2 & 3 on the fuel rail on a 1998 is a dampener to smooth out injector pulses.