89 3.2 engine hesitation

[ianmorrow]

My 89 Baltic Blue / Linen 3.2 is in great shape and ready for summer apart from one thing. On a spirited test drive it has developed a ‘ hesitation ‘ in revs at 5800 rpm. It feels like the rev limiter kicking in over all cylinders a sort of , ‘putt... putt...putt’ with minor sort of backfire. It is with a highly experienced Porsche engineer who is going through all the usual coil, distributor, leads etc but no success so far. It feels like the rev limiter is kicking in too early. He feels it is electrical rather than fuel as it is fine until high revs.
Any thoughts very welcome

[DustyM]

My 89 Baltic Blue / Linen 3.2 is in great shape and ready for summer apart from one thing. On a spirited test drive it has developed a ‘ hesitation ‘ in revs at 5800 rpm. It feels like the rev limiter kicking in over all cylinders a sort of , ‘putt... putt...putt’ with minor sort of backfire. It is with a highly experienced Porsche engineer who is going through all the usual coil, distributor, leads etc but no success so far. It feels like the rev limiter is kicking in too early. He feels it is electrical rather than fuel as it is fine until high revs.
Any thoughts very welcome

Impossible to remote diagnose but your last line "He feels it is electrical rather than fuel as it is fine until high revs. " seems backwards to me.

If it was a low fuel supply issue then it would materialise at higher revs and be OK at lower rpms, where as ignition problems would normally be more load related rather than rpm related.

If he's already check the ignition system then I'd look at the fuel pump and fuel pressure regulators. (on the rear of the fuel rails.)

[Nine One One]

http://forums.pelicanparts.com/porsche- ... ution.html

Basically flywheel speed sensor

[911hillclimber]

^^^ Agree.
Can be changed with engine in the car, but you need a deep 3/8 drive socket with a slot cut down the side and some patience!
Check the plug on the left side of the engine first for corrosion, iirc it is the white one, middle of the 3.

[Cortina]

This may be a silly suggestion (since I don't know that engine specifically) - change rotor arm ?

Said on the (probably wrong) assumption , that rev limit is governed by said item ??

[911hillclimber]

The 3.2 has the rev limit set in the Ecu, the rotor arm is solid

[Cortina]

The 3.2 has the rev limit set in the Ecu, the rotor arm is solid

Ah well , I knew it had changed - just no idea when ! ................. next !

[ianmorrow]

Thanks guys will keep you all informed. Hope it’s not the ECU as I checked price 2300£ via Porsche. A very frustrating thing to fix just hope to hit lucky early. Will keep you all informed

[Nige]

Fuel supply and/or speed sensors. But if it revs past 5.8k and is fine thereafter, I can't see it being low fuel pressure.

If there is lack of use it could be stale fuel or a sticky injector(s) that are in need of a clean?

If speed sensors they are relatively easy to swap, I did mine on the drive with basic tools. Also cross reference the part numbers as they can be had for a lot less than Porsche charge, they're used on similar vintage BMWs that use Motronic. Main thing is not to hammer or press the the old sensor out of the ali mounting bracket as it's far too easy to break or distort the bracket and that IS expensive. Just drill the old ones out, they're mainly plastic so are an easy task.

If lack of use put some injector cleaner in a tank full of fresh fuel and try and drive the problem away!

[911hillclimber]

Nige has made me think, check the clearances and that the faces of the sensors to the flywheel are clean and correct.

[dean1057]

Interested to see how this pans out as my 3.2 does the same, flywheel sensor changed and played with the gap but still the same, feels like a rev limiter when it happens.

[ianmorrow]

Hi Guys. It definitely feels like a rev limiter situation as it is a clean cut off at 5800. Goes beautifully right up to that. The engine is very clean, manic owner, so can’t see that being the issue. Dean’s experience has worried me though. Just checked an invoice for work done summer 2019 about 2000 miles ago the engine was running poorly at 5200 revs
‘ Removed air flow metre...checked ... swapped... all ok
Removed fuel rail plug confirmed fuel pressure and quantity
Confirmed mixture readings...in spec
Confirmed ignition timing, removed distributor confirmed advance bob weights free
Confirmed oscilloscope check on each injector.. good patterns
Carried out smoke test on intake manifolds inc throttle housing...good
Accessed timing chains and pulleys . Confirmed valve timing specs.
Checked resistance of coil and ignition leads
Confirmed ECU in good condition coded correctly and dry
Removed all vacuum piping and tee pieces from engine and borescope checked connections on manifolds, intake manifold sand fuel rails no air leaks
They reported they discovered a small metal plug wrongly fitted inside the tee pieces removed it and the car ran smoothly throughout range.
Now 2000 miles later here we are!!

[911hillclimber]

That IS a lot delved into.

My 140K miles 'never been apart' 3.2 runs perfectly to the rev limiter at 6400, nothing abrupt but stops the engine going further very firmly.
Stock ecu, but has the first (maybe only) Bob Watson chip in it from 1994 and is a wonderful engine.

I've a hill climb friend with a perfect 3.2 and he had a melted plug connector that upset the engine and changed the plug (the small white one on the 3 connector bracket), and all perfect after.

Odd the issue would creep back after 2k miles.

I would still check the connector first on all the 3 plugs on the left side of the engine.

[ianmorrow]

Well good result. The car now revs through the range to the red. The speed sensors were swapped for new from euro car parts 120£ . The drive shaft was removed for access and the new sensors were slightly shorter than original so bit of messing to get gap but great success. The original sensors had damage maybe from contact with flywheel. The sensors were stuck inside the bracket which had to be removed to get them out and one of the screw mountings in the casing has stripped but bracket cleaned and back on ok .Thanks everyone for advice which saved needless investigation and trying new parts. Thanks again all!!

[hot66]

Great news