Power loss after hard driving - sparks

[dr bob]

First, you'll be able to ass a lot with the plug out and a piston close to top of cylinder just peeking in with a small flashlight. The plug itself tells a lot. For the piston tops, start by looking for a cylinder with a different colored 'bloom' in the deposits.

There's a slew of very inexpensive borescope inspection camera options available at the usual online sources like Amazon. Some are as easy as just plugging in to your tablet or smartphone's charge/data port. Install their app on your device, and you can see and capture camera images. Do make sure the camera you buy has a head small enough to fit through the spark plug hole.

If you haven't used one before, the first looks inside things will be a shocking revelation, so brace yourself. Hone marks in a cylinder can show up like the Grand Canyon if/when the camera head is close to the wall.

I have a fancy but quite vintage Sony industrial camera that I bought to inspect gas turbine engine guts. Has lights and an articulating camera head. Modern stuff is a tiny fraction of what that thing cost way back when. The Good New on the Sony is that I haven't seen it in a decade now. It's still leased to a large electric utility, so I only get to see the checks.

----

Early in my adult life I was exposed to some available education in combustion dynamics at a large California oil company's labs near where I lived at the time. Their immediate goal at that moment was to build a fuel blend that would let 49-state American cars pass the ever more stringent California emissions standards. I was doing some industrial flow modeling at the time, and the chance to get involved in combustion modeling was too good to pass up. A decade-plus later, the analog 'computer' in my Saab 900 Turbo with CIS failed after a particularly, um, high-load ski trip, and living on a poor student's budget forced me to cobble a new controller. Of course, that included some improvements in mixture control under higher boost. I forced it rich to solve an annoying high-boost detonation issue, and that ultimately melted the ceramic honeycomb in the catalytic converters. That was a hard reminder of the limits and effects of excess fuel on the cats.

[icb]

Thanks for sharing that, Dr Bob. This forum is a hidden treasure trove full of individuals with very interesting backgrounds.

[Belgian951]

Update:

I had a little time to continue working on the car today.
First, I took out the crush ring from the exhaust and replaced it with a new one.
Then I checked whether the broken stud (1 of the 3 exhaust studs) was indeed a stud. It was not. The PO seemingly replaced it with a long bolt that's size 13 (instead of 17).

Then I fitted the cat pipe back in, took a bit of wiggling and some choice words, but I got it on the 3 studs and in the pipe from the wastegate.

Unfortunately, I did seem to be able to get the 2 17mm nuts back on the studs, and neither did I get the 13 mm back on the bolt. It'll be a pain to get them back on it seems, with the car on carstands and not on a lift. If anyone has any tips, including for holding down that stupid bolt that should've been a stud.... I'd be grateful.

I also checked the cylinders. Took out all plugs, two of them were oily (number 4 and 2), with number 2 very oily. All plugs smelled faintly of gas, but that's probably normal? All plugs had black tips but the threads on the non-oily plugs were 'golden hot'. The oily plug threads were, well oily.

My boroscope was unfortunately not very clear... it was a cheap Chinese unit. I did see some scratches but as far as I could tell nothing extreme... I'm however thinking of getting another boroscope that is a bit better.

[icb]

Interesting. It's not normal for the plugs to smell like gas, at least not like unburned gas, especially after a few weeks. The oily ones simply point to worn rings and/or valve guides and stem seals, which you can sort out in the future. With the oily plugs there should also be oily piston tops. If not - if the pistons look shiny clean, that usually indicates fuel washing down the piston. Black plug tips indicate a rich condition as well. I can't comment on the exhaust hardware.
If you want to pursue the mass-over fuelling idea, and it is just an idea, I would pull the fuel rail with injectors attached, pull the vacuum lines off the fuel pressure regulator and the fuel damper, and then power up the fuel pump using a jumper wire in the dme relay socket. You'll quickly know if there are any big leaks as fuel will come out of the injector tips or the vacuum ports on the other stuff. Avoid doing this if there are any open flames or other sources of ignition around your car. If the test is negative, in other words no leaking fuel, it probably rules these components out, but keep in mind this is not exactly 100% simulating what happened when you were driving that day.

[icb]

Another thing to look at is how the dipstick smells. If it smells strongly of gas there's lots of gas in your oil.

[Belgian951]

Interesting. It's not normal for the plugs to smell like gas, at least not like unburned gas, especially after a few weeks. The oily ones simply point to worn rings and/or valve guides and stem seals, which you can sort out in the future. With the oily plugs there should also be oily piston tops. If not - if the pistons look shiny clean, that usually indicates fuel washing down the piston. Black plug tips indicate a rich condition as well. I can't comment on the exhaust hardware.
If you want to pursue the mass-over fuelling idea, and it is just an idea, I would pull the fuel rail with injectors attached, pull the vacuum lines off the fuel pressure regulator and the fuel damper, and then power up the fuel pump using a jumper wire in the dme relay socket. You'll quickly know if there are any big leaks as fuel will come out of the injector tips or the vacuum ports on the other stuff. Avoid doing this if there are any open flames or other sources of ignition around your car. If the test is negative, in other words no leaking fuel, it probably rules these components out, but keep in mind this is not exactly 100% simulating what happened when you were driving that day.

Thanks again for the insight! I just received the new boroscope, I hope it's a bit better. Should be 1920P but meh, doubt it. I do recall that two pistons were black and others not... I'll have to re-inspect them and take notes.

If I take the fuel rail off with the injectors, and jump the fuel pump, will the fuel come out forcefully from the injectors, or will there perhaps be a dribble (and if perfect, nothing)?

I'll def. smell the dipstick..

[icb]

Yes, pressurizing the injectors without the engine running should result in nothing coming out - the injector valves are (or are supposed to be) closed when there is no electrical current flowing in the injector coil.

Frankly, there are so many potential small pieces to this puzzle that I'm finding it hard to make short, simple suggestions. I'm sorry if I'm long-winded.
I also think that there are quite a few people here that know way more than me about these kinds of things.

Anyway, I think it is a good idea to do the fuel rail / injector leak test. If only a tiny amount of fuel dribbles out, that is a problem, but probably not enough of a leak to cause the glowing cat situation. To do that, there would have to be a fair amount of fuel leaking out of them. Think stuck open injector (possibly sticking only when it gets hot - after all, they are 40 year old electro-mechanical devices), or a really bad O2 sensor making the DME send way too much fuel. Don't forget to also check the vacuum ports on the regulator and damper while you're at it. If you find fuel streaming out of either of those, that's a massive rich condition right there.

In the event that your injectors , regulator, and damper test absolutely leak-free, consider that any misfire is going to pump raw gas and air/oxygen right into the exhaust, which will be ignited and burned in the cat, heating it up. Misfires could be due to a bad ignition component (plugs, wires, cap, rotor, coil), even bad fuel, water in the fuel, or a bad head gasket. Any of the electrical components I listed could also be affected by wiring harness or grounding problems. And of course, any of these conditions (including a clogged cat, which is the end result of continued operation with these issues) could have existed before you bought the car!

Lastly, here are a couple of other checks you could do:
1. If you can (want to try to) get the engine running again, let it warm up, then measure the temperature of the pipe at the inlet and outlet of the cat with an infrared thermometer. The difference between inlet and outlet temperature should be 50 degrees F or less. A temp difference over 100 F indicates a clogged cat.

2. Measure the exhaust back pressure either at the CO test port if you still have it, or remove the O2 sensor temporarily and measure it there. You should measure less than 3-4 psi at idle. You'll need either an actual back pressure test gauge or an old-style vacuum/fuel pressure tester gauge and suitable adapters.

[Belgian951]

Yes, pressurizing the injectors without the engine running should result in nothing coming out - the injector valves are (or are supposed to be) closed when there is no electrical current flowing in the injector coil.

Frankly, there are so many potential small pieces to this puzzle that I'm finding it hard to make short, simple suggestions. I'm sorry if I'm long-winded.
I also think that there are quite a few people here that know way more than me about these kinds of things.

Anyway, I think it is a good idea to do the fuel rail / injector leak test. If only a tiny amount of fuel dribbles out, that is a problem, but probably not enough of a leak to cause the glowing cat situation. To do that, there would have to be a fair amount of fuel leaking out of them. Think stuck open injector (possibly sticking only when it gets hot - after all, they are 40 year old electro-mechanical devices), or a really bad O2 sensor making the DME send way too much fuel. Don't forget to also check the vacuum ports on the regulator and damper while you're at it. If you find fuel streaming out of either of those, that's a massive rich condition right there.

In the event that your injectors , regulator, and damper test absolutely leak-free, consider that any misfire is going to pump raw gas and air/oxygen right into the exhaust, which will be ignited and burned in the cat, heating it up. Misfires could be due to a bad ignition component (plugs, wires, cap, rotor, coil), even bad fuel, water in the fuel, or a bad head gasket. Any of the electrical components I listed could also be affected by wiring harness or grounding problems. And of course, any of these conditions (including a clogged cat, which is the end result of continued operation with these issues) could have existed before you bought the car!

Lastly, here are a couple of other checks you could do:
1. If you can (want to try to) get the engine running again, let it warm up, then measure the temperature of the pipe at the inlet and outlet of the cat with an infrared thermometer. The difference between inlet and outlet temperature should be 50 degrees F or less. A temp difference over 100 F indicates a clogged cat.

2. Measure the exhaust back pressure either at the CO test port if you still have it, or remove the O2 sensor temporarily and measure it there. You should measure less than 3-4 psi at idle. You'll need either an actual back pressure test gauge or an old-style vacuum/fuel pressure tester gauge and suitable adapters.

Thanks for the reply.

I think it's more likely to be injector related as the O2 sensor is brand new and original Bosch. The vacuum ports have been checked multiple times after running, but never during running. No fuel in the lines.

The fuel rail itself is also brand new Porsche original part as are the injector seals. Plugs are new Bosch original wr7dc, have maybe only a 100-200 km on them.

I didn't change the wires, cap or coil though. The rotor was changed (brand new Bosch again) because I broke it when doing the timing belt.

Bad fuel... Could be residual fuel that's 2 years old. But I filled the tank when the empty fuel light came on, so it should be 95% new fuel mixed with bad fuel (and admitedly probably too much fuel stabilizer).

Bad head gasket... Could be, since I'm suspecting I'm losing coolant somewhere, but I haven't yet seen white smoke, nor boiling/bubbling coolant tank, or oil in the coolant. I'll keep a close eye on my coolant though. Grounds or harness, definitely a posibility as several connectors and wires seem to be close to disintegrating.

Is the cat temp test still valid if the filter medium has been removed? I hammered out all the stuff now.
Relatedly, I believe once I get the exhaust back together, the same issue that started this thread shouldn't pop back up, correctly? As no cat = no overheating cat/pipe, right? The extra gas would just get blown out the tailpipe?

I think I'll def try to check the cylinders again and do the oilstick smell test, and then try to start it so I can drive the car back to my garage. Then I can do more comprehensive work. Or is this a Do Not Drive situation?

[icb]

No, I think you can run it to do some troubleshooting. If you have hollowed out the cat, I'd say you're good to go. All that's really left is to make sure your fuel delivery is all working properly, in the interest of performance and minimal engine wear/oil life. If the oil is full of gas you will want to change it fairly soon.

[Tom]

I'd replace the wires, plugs, cap and rotor. More often than not when a 951 runs well normally, but stumbles on boost, it is due to weak ignition. Could be all sorts of things, of course, but if those parts are of an unknown vintage, it's not a waste of money anyway, and very well could resolve the stumble.