Carrera enging dropping a cylinder, briefly

techweenie · techweenie's Garage

I don't have a lot of time on this engine. It's an '87 Carrera with backdated exhaust. Lambda sensor in the pipe from the left bank...

It's been trouble-free, starting and running well for all the 800+ miles I've put on it so far. But recently, on a couple of steady freeway drives, it has stumbled a bit on steady throttle or slight decel. In all cases, accelerating a bit makes the stumble go away.

It's weird. It kinda feels like carburetor problems I've had in the distant past.

But this is a stock Motronic system. The problem seems to happen between 3-3300 RPM, if that helps.

I did a search, but the Motronic problem threads here are mostly DME relay related, and more binary in nature.

Oh, and the fuel pump is new.

Any clues?

ChkbookMechanic · ChkbookMechanic's Garage

This might be a completely stupid idea and might not solve the problem but being an ECU controlled car did you consider an ECU reflash/chip to take care of the less restrictive exhaust system now on the car?

Just throwing ideas out there: did you check all the connections from engine to ecu or the throttle cable and accelerator connections?

techweenie · techweenie's Garage

Not a stupid idea at all. I live in Steve Wong territory, after all. Just saving up (laid off 5 months ago).

I didn't check connections, because this didn't seem to me to be relatable to connections. I could easily be wrong on that, though.

DW SD · 04-23-2009, 10:04 AM

I wonder if it might be your barn door air sensor? The tracks wear on the variable resistance wiper. It would make sense that some change in throttle would resolve the issue. If the engine has some miles on it, especially freeway driving, there might be more wear at that spot (freeway speeds, cruising throttle).

There are plenty of posts here of how to remove, disassemble and repair.

Doug

911st · 04-23-2009, 03:13 PM

+1 on the tracks in the AFM. The internal arm can be readjusted so it rides on another part of the tracks.

techweenie · techweenie's Garage

Thanks, guys. I grabbed the Word doc with info on the AFM. I'll be tackling that puppy in the next few days...

Zeke · 04-23-2009, 03:58 PM

I have had the same problem, but not at the same circumstances. On one occasion, I had to get the car out on the freeway and get some heat in it and it caught on all 6. I have suspected the individual fuel injectors so I bought some used. I've not taken the time to install them, so I guess I'm not much help.

Still, part load on an injector that is dirty or malfunctioning in some way might manifest in stumbling. When you hit the gas, maybe the increased time the injector was open gave you enough fuel to light the cylinder and it stayed flowing well enough until the next incident. Only a postulation on my part.

All I know is that fuel injectors can act up like this.

MURF · 04-23-2009, 04:23 PM

i converted mine to new bosch series 3 injectors..do a google search multiport no pintle..very nice better partial throttle response and no internal metal no clogging issues +++++++

Zeke · 04-23-2009, 04:51 PM

Quote:

Originally Posted by MURF

i converted mine to new bosch series 3 injectors..do a google search multiport no pintle..very nice better partial throttle response and no internal metal no clogging issues +++++++

There is an extensive thread about 3.2 injectors here and I think your info should be added for the Wiki.