Power loss after hard driving - sparks

[Belgian951]

Thanks both, I'll recheck the cylinders with my new boroscope, refit the exhaust pipes, and start her up. I'll provide a new update asap.

[Belgian951]

Hi everyone,

big update here.

So yesterday and today I had some time to work on the car. I was hoping I could finish it on Saturday, but that blasted bolt the PO put in the downpipe instead of a stud really took me for a spin. Today, I ended up just putting it back in without the tiny washer that was also on there. I tried getting a new bolt, grinding down that bolt, getting another one, grinding that one, ... I just gave up for now.

So the good news is that after too many hours of struggling with this bolt, I go the complete exhaust back in. I think I'll have to remove the back section again later because the four bolts that hold it to the cat section seem unable to completely close the sections together. It's like that big sealing ring isn't seated 100% correctly in the exhaust. But for now, it should do.

After this rather horrible experience, I reinstalled the starter motor and the various skid plates. I then proceeded to check the cylinders with my new, and indeed improved, boroscope. The results are.. well

Cylinder 1: was on top, couldn't boroscope. but the piston was very blackened and oily.

Cylinder3: piston again very black, oily looking. Has what seem several scratches including a strange dark patch on the cylinder wall. See pics here:

Cyl 1 (2).jpeg (60.9 KiB) Viewed 615 times

Cyl 1 (3).jpeg (60.59 KiB) Viewed 615 times

Cyl 1 (1).jpeg (57.54 KiB) Viewed 615 times

Cyl 3 (1).jpeg (46 KiB) Viewed 615 times

Cyl 3 (2).jpeg (51.61 KiB) Viewed 615 times

Cylinder 4: less blackened piston, less scratches it seems. See pics here:

Cyl 4 (1).jpeg (61.13 KiB) Viewed 615 times

Cyl 4 (2).jpeg (62.72 KiB) Viewed 615 times

Cyl 4 (3).jpeg (59.37 KiB) Viewed 615 times

cylinder 2: was on top, couldn't boroscope.

After boroscoping the cylinders, I refitted the fuel sparks and reattached all cables. I tried to crank the car, but it wouldn't start. And the strange thing was that even when I turnt off the key and removed it, the car kept cranking! It only stopped when I removed the battery cable. I tried to start the car again immediately after, and it did the same thing.

Oh and I also checked the dip stick for fuel smell. It did smell distincly of fuel. Should I change the oil?

So now I have a refitted hollowed out cat, but the car still doesn't start.
Hopefully someone here has any idea what to do!

[icb]

Hi!
Others might disagree, but if it were me, I would change the oil and the filter before doing anything else. It's no longer really oil with a ton of solvent in it, and you could be doing a lot of cranking over the next little while. Your pics of the cylinders look good to me and I don't think they show anything out of the ordinary, maybe just a few small minor scratches from years of use.

On your no-Start issue: Not to be insulting, but did you put the DME relay back in after the fuel pump test?

On the starter running-on issue: Check that the S wire (the small one) is not touching the big power cable on the starter solenoid.
If that checks out OK, disconnect the battery, then disconnect the main starter cable, and the small S wire from the starter. Make sure these are not going to touch anything, then re-connect the battery. Have an assistant check the S wire with a voltmeter or a 12V test light while you put the ignition key in and turn it from Off to Run to Start, then back to Run, then Off. Anything other than 12V in Start at the S wire indicates a problem with the starter switch or its wiring. This would be unrelated to your original problem. If, on the other hand, the voltage is correct from the ignition switch, it is possible that the heat from the overheated exhaust/cat damaged the starter and the solenoid is sticking on.

Once you get the starter to work properly, you can attack the no-start, if it wasn't the DME relay being unplugged. But you probably know, check the simplest things first - fuel, air, spark.

[Tom]

Hi!
Others might disagree, but if it were me, I would change the oil and the filter before doing anything else. It's no longer really oil with a ton of solvent in it, and you could be doing a lot of cranking over the next little while. Your pics of the cylinders look good to me and I don't think they show anything out of the ordinary, maybe just a few small minor scratches from years of use.

On your no-Start issue: Not to be insulting, but did you put the DME relay back in after the fuel pump test?

On the starter running-on issue: Check that the S wire (the small one) is not touching the big power cable on the starter solenoid.
If that checks out OK, disconnect the battery, then disconnect the main starter cable, and the small S wire from the starter. Make sure these are not going to touch anything, then re-connect the battery. Have an assistant check the S wire with a voltmeter or a 12V test light while you put the ignition key in and turn it from Off to Run to Start, then back to Run, then Off. Anything other than 12V in Start at the S wire indicates a problem with the starter switch or its wiring. This would be unrelated to your original problem. If, on the other hand, the voltage is correct from the ignition switch, it is possible that the heat from the overheated exhaust/cat damaged the starter and the solenoid is sticking on.

Once you get the starter to work properly, you can attack the no-start, if it wasn't the DME relay being unplugged. But you probably know, check the simplest things first - fuel, air, spark.

Agreed on all counts. I had a 944 starter do this on me. On true Bosch starters, there is a barrier/wall between the small wire and the big power post. On a lot of the cheap rebuilds, however, that barrier isn't there and it's very easy to rotate the little connector until it hits or almost hits the big post. Mine didn't make electrical contact right away, but in the middle of the night when it got wet with dew, it fired up the starter and chugged away into the garage until the starter cable completely burned out -- literally looked like a long cigar ash. Of course, solenoid could be sticking too, which is fairly common. Once you sort the starter, I'm guessing it's just a matter of finding that d'oh! thing that didn't go back together right.

The cylinders look pretty typical to me. These motor can run very well with worse cylinders -- ask me how I know. Not sure that caused that black area at the top of that cylinder, but maybe some kind of ring issue that had to work itself out...

[Belgian951]

Thanks again both!

I'm relieved to read that my cylinders seem fine! I'll do the oil change first thing. Would adding 'Slick 50' help? My mechanic teacher said it would help protect the cylinders. It makes sense to also do the fuel loss test ICB described earlier... don't want to change oil every 500 km lol!

It is possible that the small S cable to the starter is touching something it shouldn't. I did rotate it upon reinstallation, I remember. And it definitely is not an original Bosch starter (same format though), the PO changed it.

I verified that the DME relay is in the fuse box.

I'll recheck any cables and connectors that I perhaps didn't refit.. But I only touched the air filter box, the AFM, the throttle body (and black sensor near it), the intercooler hard pipes and the J-boot to check on the turbo. After refitting, I took off the protection plates on the bottom, the starter and the exhaust pipes. So anything I forgot to reconnect should be situated there. I'll double check everything to be sure.

[icb]

No Slick 50! Or any oil additives for that matter. Resist the urge, don't do it!!!
Your engine only needs a high quality oil with suitable quantities (for an Alusil engine with flat cam tappets) of moly and zddp in it. Personally I recommend Driven DT50, which is on the expensive side, but your engine is worth it. There are other oils out there with suitable amounts of moly and zddp. Note that more is not always better, it must be enough and be a balanced package. Many people like Valvoline VR-1 oil also for the 944 engine. Take a look at some LN engineering and Motor Oil Geek videos on YouTube for more insight on this.
Good plan on the other stuff.

[Tom]

No Slick 50! Or any oil additives for that matter. Resist the urge, don't do it!!!
Your engine only needs a high quality oil with suitable quantities (for an Alusil engine with flat cam tappets) of moly and zddp in it. Personally I recommend Driven DT50, which is on the expensive side, but your engine is worth it. There are other oils out there with suitable amounts of moly and zddp. Note that more is not always better, it must be enough and be a balanced package. Many people like Valvoline VR-1 oil also for the 944 engine. Take a look at some LN engineering and Motor Oil Geek videos on YouTube for more insight on this.
Good plan on the other stuff.

100% agree. They also sell xddp/zinc additives, but no real reason not to get an oil that already has it...

[Belgian951]

Thanks again for the advice. I won't add anything else than oil. I just ordered a new oil filter, and I still have the necessary fresh oil in stock. Hoping to fix the car in the second week of July!

[dr bob]

Outside perspective --

On the starter run-on, it's certainly a Good Idea to double-check the connections where the 50 (trigger wire) connects. Look for contact with the wire from the solenoid to the starter motor. Even then the symptom doesn't really point to an external contact issue with either that one or the battery cable terminal.

Making a rash assumption that your starter arrangement is similar to the one in my 928 car, look at the other small connection on the solenoid. On some early 928 cars, this contact receives battery voltage at the same time the starter motor does, via and aux contact point for the copper contact disk inside the solenoid housing. Internally, the solenoid has a magnet that draws the the drive gear at one end to engage the flywheel. At the other end, there's a copper disk that connects the battery post bolt and a similar bolt for the starter motor feed wire, plus it bridges to that third contact point. I would look there at the second smaller screw/terminal for something bridging. You can use your DMM to check if there's continuity between the two smaller connections at the solenoid. If you don't see an external connection issue at those terminals, but you do see continuity between the two, your troubleshooting should move to the wire harness to the starter, for an internal short.

If your car has a starter interlock relay, common to auto gearbox cars and some with clutch pedal interlock safety switches, stuff a new relay in the socket. Before you do, use your DMM to check for signal from the ignition switch while the relay is out of the socket. It needs to show battery voltage with key in 'start' position and go open (no contact/voltage) when key is relaxed. Sometimes a test light is a better indicator, since you can follow the contacts action more easily as you cycle the key position.

We've seen an abundance of counterfeit ignition switches in the market over the last 10+ years now. If you decide you need to replace the switch, be sure to buy it from a reputable supplier. My 928 shares a switch with the 911 cars from the same time period, making the cheap-copies business significant. I don't know if your 944/951 shares that switch, but regardless use a good one if you replace.

[Belgian951]

Outside perspective --

On the starter run-on, it's certainly a Good Idea to double-check the connections where the 50 (trigger wire) connects. Look for contact with the wire from the solenoid to the starter motor. Even then the symptom doesn't really point to an external contact issue with either that one or the battery cable terminal.

Making a rash assumption that your starter arrangement is similar to the one in my 928 car, look at the other small connection on the solenoid. On some early 928 cars, this contact receives battery voltage at the same time the starter motor does, via and aux contact point for the copper contact disk inside the solenoid housing. Internally, the solenoid has a magnet that draws the the drive gear at one end to engage the flywheel. At the other end, there's a copper disk that connects the battery post bolt and a similar bolt for the starter motor feed wire, plus it bridges to that third contact point. I would look there at the second smaller screw/terminal for something bridging. You can use your DMM to check if there's continuity between the two smaller connections at the solenoid. If you don't see an external connection issue at those terminals, but you do see continuity between the two, your troubleshooting should move to the wire harness to the starter, for an internal short.

If your car has a starter interlock relay, common to auto gearbox cars and some with clutch pedal interlock safety switches, stuff a new relay in the socket. Before you do, use your DMM to check for signal from the ignition switch while the relay is out of the socket. It needs to show battery voltage with key in 'start' position and go open (no contact/voltage) when key is relaxed. Sometimes a test light is a better indicator, since you can follow the contacts action more easily as you cycle the key position.

We've seen an abundance of counterfeit ignition switches in the market over the last 10+ years now. If you decide you need to replace the switch, be sure to buy it from a reputable supplier. My 928 shares a switch with the 911 cars from the same time period, making the cheap-copies business significant. I don't know if your 944/951 shares that switch, but regardless use a good one if you replace.

Thank you for your insights! Here's a picture of the starter that's in 944 turbos. Could you point me to the area you suggest me to check for continuity (I marked your text in bold to what I'm referring to here). https://partworks.de/partworks/en/12233 ... otor-1.7kw