3.2 losing power at track

[shaunmbenson]

Hi gang

3.2 with SW chip and m and k premuffler/muffler with new oxygen sensor.

Car was running brilliantly for 3000kms since chip muffler sensor install. Now at track losing power and it stutters and either comes back or drops again. Stalled on one lap upon exiting track

I mention the chip etc cause last ear my stock car had no issues on same track

Should I swap chips back or am I looking at ther issues?

Currently driving home and no problem unless I floor it

Help!

[Tippy]

Head temp sensor could be going overichening muxture (ECU thinks the engine is cold, crank sensors can be going, or components in the ECU are overheating.

Those are a few things that spring to mind.

[Steve W]

It could be anything including a failing fuel pump, DME relay, or the DME unit itself. But my suspicion is the DME unit itself is failing because of the stutters and stalls. Eventually the car will not start. I estimate at least 30% of 3.2 have had this problem and had a replacement unit or had the original repaired, or if it hasn't yet will eventually. You may want to have your unit checked and repaired as necessary, or try swapping units with another car to see if the problem transfers/goes away. I doubt its the chip as that's not a normal failure mode of a chip, but you can try it and you'll see the car will still have the same problems.

[stlrj]

SW chips tend to run a bit rich so your plugs may have fouled. Easy enough to change them.

[Steve W]

They actually run fine, not sure where you get the rich opinion from unless you had one of my chips in your car and it messed with the air flow meter so it runs on rich side overall.

The stock chip actually dumps too much fuel into the motor after 5000 rpm, running AFRs into the 11s. I actually remove and lean out the fuel mixture above that to a leaner 13 range at full throttle where it is optimal and makes the best power. And as the OP has notice the problem at the track, where standard operating procedure is to drive between 4500 to 6800 rpm at full throttle 90% of the time, I doubt his problem is a rich mixture related one.

[shaunmbenson]

So I just pulled SW Chip and replaced with stock -- car ran worse. That to me was good news cause I've raved about the effects of the chip so I'm glad that wasn't the issue.

I then went back to DME -- put SW chip back in and reworked my solder points that looked a little suspect from back when I made it a 4k board. The chip had been bought used from a later 3.2 car.

I then thrashed it as best I could around my neighbourhood and was unable to replicate the issue -- tomorrow back at the track will be acid test.

Thanks for the thoughts guys -- and Steve you may be getting a DME swap from me shortly if my fix didn't fix it!

I'll let y'all know. The good news about this being a hobby is that even though my day didn't go as planned it's still a Porsche filled Saturday and I got to learn some stuff.

[Steve W]

Cool! Yeah, if you didn't solder that 4k jumper properly with proper heat and solder flow, you'll have a cold joint there which would cause the same problem.

[Cory M]

Check your reference sensors

[stlrj]

[QUOTE=shaunmbenson;9110335 Now at track losing power and it stutters and either comes back or drops again. Stalled on one lap upon exiting track
Help![/QUOTE]


It still sound like an ignition problem. Chips and mixture issues usually do not cause sudden intermittent stutters.

In other words, nobody chips their 911 to cure a sudden intermittent stutter.

[Krieger914]

I chased this intermitant problem on a carbed 3.0 914/6 track car for more than a year. Additionally my oil temps would rise when I had the problem forcing me to get off the track. The wind up was an oil scavenge problem. The oil pump was not getting the oil out of the engine case. All the internals were banging their way through about 5 quarts of oil in the engine case! Check the oil level in your tank ASAP when you have the problem. The problem in my motor, when I finally pulled it apart, was that two of the four nuts holding the oil pump together were finger tight...It was sucking some oil up and spraying it back into the engine case.

[Quicksilver]

Every person who has seen a similar problem will have seen the failure specific to their car so they may suggest something that may be the issue or just as likely it will not be related.

A couple basic things....
- Vacuum leaks effect the motor more when you have an intake vacuum (idle or part throttle) so that doesn't describe your issue.
- Items that do run towards your issue: Limited fuel supply effects the car as power output rises so that requires checking. The higher the cylinder pressure and the higher the RPM the harder it is for a spark to jump so your coil and whole spark path bears examination.

Test, test, test. Sensors, connections, electronics (DME) all should be tested.

[ischmitz]

Mixture being off or poor park WILL cause stutter and poor running.

My 3.6 has had several occasions where the engine ran poorly to the point of cutting out badly at cruising speeds. At the time I was 100% convinced it was spark-related or electrical (loosing power to the DME). However, it was a poor connection of the O2 sensor letting the mixture go all lean. The symptoms where highly intermittent. On another occasion a poorly seated connector the AFM did the same.

Then a clogged fuel filter caused stutter, stalling, poor starting. There really isn't any telling what is causing poor running. Missing fuel, too much fuel, weak spark all have the same effects: Sputter, rough running, no-start.

In summary almost anything not optimal with a DME-controlled engine will cause poor running, and most sensors affect mixture. The only way to get to the bottom of things is proper diagnostics.

[shaunmbenson]

Just wanna close the thread for anyone in future

So I ordered a new DME with a chip I knew was compatible. Having bought a used SW chip for a later car and having rewired my DME I just wanted to know, moving forward, that I was warrantied and my DME was tight. This was probably overkill and unnecessary but I was happy to do it.

After that the trouble persisted so with the help of Hunter Motorsports in Mississauga = cylinder head temp sensor.

Now she is right as rain and I can't wait for the next track day.

Thanks for all the input

[DRACO A5OG]

Oh Congrats!

[Tippy]

I'm confused, was it head temp or DME that fixed it?

[shaunmbenson]

99 percent head temp -- the 1 percent was what I called my overkill.
In other words the new DME didn't fix it until the head temp sensor was replace

[ischmitz]

CHT makes sense. It'll let the engine go all rich if it makes poor contact. It probable was the old one-wire version relying on GND through it's threaded housing. And as the thread corrodes it fails and reads nonsense.

The DME either works or it doesn't. If you had put in a wrong jumper it would have been completely brain-dead not even making the engine stumble due to zero spark or fuel. This is a very black&white behavior.