PIP or TFI Gone Bad?

[doctorj357]

Yesterday my 95 GTS started exhibiting a random stall driving. It jused to do before while idling, but now its while driving. It definitely feels like ignition cause its a instant OFF! Yesterday it happened 3 times. Twice while stopped at light, and once while driving, and a couple times in between while driving, for a quick split sec it jerked really hard like the engine seized up but immediately recovered. And for each time it stalled completely, it wouldn't restart right away. I drove it earlier that day, 4x the distance and had no issues what so ever.

I did check for codes, none found other than the standard 511(ROM Failure due to CHIP) and 111 (System Pass). First to explain some initial symptoms when I picked up the car last summer and what I've done to it since:

From the beginning I have had

• random occurrences of the car stalling only while idling
• smelling uber rich at all times
• frequent surging idles
• lightly sounding like its missing when at low speeds

Since then I have replaced/performed the following

• vacuum leaks, found a couple and fixed
• IAC
• IAT
• ECT
• Coil / Wires / Plugs
• Cap & Rotor
• Fuel Filter
• O2 sensors
• Base idle reset
• TPS adjustment
• Checked fuel pressure
• TB cleaned
• Dialed timing back to 10deg
• Chip (Bama) yes I know

I know some of that was taking a shot in the dark and ended up in a buying frenzy where I was just replacing parts. Somewhere along the way, something seemed to solve my surging idle at least. But the random stall, smelling rich and sounds of missing was still occurring.

Then 3 days ago, a little light bulb went off. I recalled original owner admitting to having a colder Tstat put in. What the hell its only $10. Put in a new 195 and new gasket. Old one pulled was a 180, which didn't seem cold enough, but would appear it was stuck partially open. That makes total sense, engine never really got to the optimum temperature and and ECU would richen up the mix. Since the 195 went in, its like a new car. Definitely no more smell (other than standard cat less exhaust), drives smoother, but the mileage is TBD since I not driving it right now.

I'm wondering if my PIP or my TFI has been suspect all along and just recently exasperated since the changing of the Tstat. Which in theory should be causing more heat soak now. The distributor is original, but car only has 57k on it. Is there any easy way to test either sensor or do you have to pull them for testing?

 

[jozsefsz]

I'd just replace them both if in doubt or if you don't know if / when they were last changed (I've had my 95 since 96 and changed them both twice over the years).

They'll cause annoying stalling / refuse to start until cooled off issues when you least need them. Usually when the PIP lets go (it's usually the first suspect), the TFI isn't far behind. Even though it's remotely mounted and will last longer than on a Fox, they burn up under their own heat once the heat-sink grease gets old and hard. PIP can be replaced if you're reasonably careful, or get a new distributor (definitely new - many remans come with old PIPs and fail out of the box). TFI's easy if you have the right mini socket. Neither is unreasonably expensive and will give you peace of mind.

 

[doctorj357]

Yeah that's kind of where I"m leaning. Both parts are factory orig. So low miles, but they're aged now.

I did pull the TFI tonight and will take it to a autozone or o'rileys tomorrow and have them test it. Fingers crossed it fails, but if not, I'll shift focus to the PIP. Is there a reasonable test that can be done while the pip is installed, wires...volt meter...etc? Or does that unit have to come out?

 

[jozsefsz]

I think you can check the resistance of the PIP, but that's not a very valuable test. The TFI will absolutely test fine at the parts store unfortunately even if it's broken. As you know, it's perfectly fine when it's cold. Unless the guys at AZ will let you hold a torch to it while they're testing it, you're better off just replacing. Same with the PIP, it'll be fine when it's cool.

 

[doctorj357]

Well ironically the factory TFI failed the Hi/Low test at Advance Auto. But then so did a brand new in box BorgWarner. I think their machine is out to lunch. But even if it wasn't, they didn't have any more in stock and impatient me, I tried a Duralast across the street from Autozone.

Can't say I"m convinced it solved my issues, but I took it for a short jog (8mi) after 10min warmup in the driveway. No issues as of yet. Right now the weather in MI is the typical crap snow/rain. Waiting for another good day to take it out. But even if this fixed it, I might still replace the PIP anyway for peach of mind. Hope to have an update by end of the week.

 

[doctorj357]

Soooooooo, new TFI (Duralast)... not sure how much I trust that , got install, and also a new Cardone Select dizzy. Set my base timing to 12deg TDC, with the spout out. Took the car out for about a 10mil drive to get it nice and hot. Nothing missed, pinged or detonated. BUT, towards the end of the drive it started to act up again like before

• Driving along the car would jerk/buck real hard for a split sec, almost like the engine locked up briefly and then it instantly resumed to normal
• Coming to stop lights the idle would drop down to where I set it, 950, but when I gave it throttle to go, it started to stall out unless I compensated with the gas

Good news is, the car didn't stall or die on me while driving like before. Additionally I think the new dizzy, or PiP inside at least fixed a hunting idle I've been randomly seeing. Bad news is, I think I'm still suffering a issue related to heat soak as it only started displaying symptoms long after the engine was hot and driven for 7-10mi.

The only piece of evidence that happened today that's convincing me might be something else, the car didn't die like before. It instead would just start to stall out but I could catch it in time. Before, it was just an instant off with no warning.

 

[jozsefsz]

I guess that's some good news? Bucking and off-idle hesitation when fully warm (car enters closed loop) sounds like a fueling issue. Since you've replaced your O2's (often the cause) I wouldn't suspect those unless they got really carbon-fouled during previous stalling incidents. You might try pulling one just to see. I've had a dying fuel pump (not very old one) cause issues during hot days so a fuel pressure check (borrow a gauge from AZ) might also be good when it's acting up - at least it's close to free. A MAF cleaning might also help - if the MAF is really dirty it can cause similar issues.

If it's neither of those few things (O2's and MAF dictate closed-loop (engine fully warm for at least a few minutes is when this kicks in) along with expected fuel pressure and what's in the tune), I'd go back to Bama and have them adjust your closed-loop fueling. With a datalog they should be able to address your driveability symptoms.

Only other thing I'd try is a 'cylinder balance test' which is part of the KOER test cycle (after this completes, stomp the gas, and it'll let you know if any of your cylinders is putting out more or less power than the others) - this can help pinpoint if you might have a faulty fuel injector somewhere. I don't consider this as likely as you'd also have problems in open-loop (before it warms up) then.