TS motronic wont rev past 5000

[Divano Veloce]

Hi All,

im preparing a TS for Broadford and it doesnt want to rev much past 5000 rpm. Around 5000-5500 it starts to ping fantastically and looses all power. Up to 5000 its running better than ever. It hasnt always done this and it will do it with any fuel. Plugs and leads are new, fuel filter is new.

Please state the obvious and obscure likely causes and remedies!

Cheers,

Matt

[Divano Veloce]

I have a second TS i can pilfer parts off if need be for fault finding...

[jazig.k]

Can you check the timing while revving up to the problem area, make sure nothing odd is happening there?

[Divano Veloce]

Alas i have no timing light.. Might be able to borrow one tomorrow and investigate. Good suggestion.

I may have read something about the CAS and/or its wiring playing up. Is there a way to test this?

[Mick A]

maybe try another air flow meter.

[Duk]

Alas i have no timing light.. Might be able to borrow one tomorrow and investigate. Good suggestion.

I may have read something about the CAS and/or its wiring playing up. Is there a way to test this?

You can't change the timing on the Motronic run engines.
The crank angle sensor is fixed in place and moving the distributors around means nothing other than potentially having the ignition lead post (in the distributor cap) in the wrong place when the rotor button travels past.
Make sure you have at least 95 octane fuel in the tank. Other than that, it's time to start fault finding.

[jazig.k]

I have a timing light you could borrow. Only a cheapie but it works last time I used it... If i'm working tomorrow I can bring it to Castlemaine.

[GTVeloce]

The crank angle sensor can be easily tested. Just pull the lead off and measure the resistance across the two leads. From memory it should be about 900ohms. It must be getting power to it or the engine wouldn't run at all. Check it is reasonably clear of gunk too that might be interfering with the signal and that it is within 1mm (IIRC) of the pulley.

Like choderboy said, I would be leaning toward the air flow meter or a part of the basic ignition system. Checking the timing won't hurt but I doubt that is what is causing it given the engine runs well below 5k. However, the other parts of the ignition system could be failing at high rpm although given that it runs two systems effectively makes me think it is further up stream. Easy to check; disconnect one of the coil leads and see what happens then reverse.

Given you have a spare, an AFM swap would be a very quick test...

[Mick A]

Forget the timing light please. You don't need it.

Also crank angle sensor is unlikely to be the cause of this fault. They generally simply stop working when they get hot.

[AikenDrum105]

you could check the VVT wiring and relay - the connectors on the VVT itself are notorious for temp-cycling loose (and getting covered in oil)  which might cause an issue at higher RPM...   

You could also try running the car on just one coil (and 4 plugs)  at a time, in case you're getting spark breakdown or leak at higher rpm on one dizzy stuffing things up.  While doing 105 / 116 conversions I've come across a *lot* of twinsparks with one or two dizzies leaking spark through the rotor button to the shaft...   They're usually glued on so are a break-off-and-glue-new-one-on  proposition.

Good luck !

Cheers,

[Mick A]

Yes I agree definitely check the dizzy caps and rotor buttons.

I thought in the first post he said these were new but I re read and I see just plugs and leads sorry.

[Duk]

The crank angle sensor can be easily tested. Just pull the lead off and measure the resistance across the two leads. From memory it should be about 900ohms. It must be getting power to it or the engine wouldn't run at all. Check it is reasonably clear of gunk too that might be interfering with the signal and that it is within 1mm (IIRC) of the pulley.

The Motronic CAS are Variable Reluctor and don't have any power sent to them. They are excited by each of the passing teeth and give off an AC signal as a result.

[bowds116]

Mine did something similar, new fuel filter fixed it. Also check the earth leads to the cam cover.

[Divano Veloce]

Thanks everybody for your responses. I have changed out the AFM but have not tested it yet... Car is otherwise good to go. I'll fill it up with 98 and let you all know how it goes tomorrow

[Divano Veloce]

Thanks everyone for your help on this problem. Swapping out the AFM has fixed it.