2.4 on MFI: sudden reduction in power

[2.4TE]

I recently had a rare opportunity to take my 2.4MFI 911 out for a drive, just for the heck of it. For the first time in 21 years of ownership, it almost let me down: I'd warmed it up as usual and then started to drive it 'with sprirt'.

After a few minutes it was suddenly down on power, like driving my old 998cc Mini.

I'm working my way through 'Check Measure Adjust' and so far (just done compression test) cannot find the likely cause.

I'm almost at 'measure fuel pressure' and want to ask: how do I do that?

Also, looking ahead, if it was my fuel injectors, has anyone experience of home cleaning/testing? I see you can buy a test rig from the US at 'mercedessource'. Good idea? Any alternatives?

Any thoughts on likely causes of sudden loss of power, given compression looks fine?

Many thanks in anticipation for the collective wisdom.

[hot66]

Look at the basics first ... ignition points ? Throttle opening all the way ?

Then, is the thermo hose connected or split ... excessive running rich can cause drop in power

[inaglasshouse]

Yep, keep it obvious... My money is on electrical not fuel system.
Points and other distributor woes... start by checking timing, which will tell you if the points have moved or the dizzy is not advancing properly. Both can immediately create the symptom you describe.
HT leads? Still attached? Condition?
Coil? Got a spare to swap in?
CDI? Got a spare to swap in?

Fuel system
Fuel blockage? If you don't get a chance to drive often, is there gunk in the tank? Quite easy to have a look by removing the sender. And to take off the fuel filter in the engine bay. The filter in the tank is a bit more of a pain to get to.
Pump / pressure - start by seeing if the pump is making funny noises or leaking. If not it's probably fine.
Injectors - yes can degrade performance, but seems unlikely they are to blame for sudden serious loss of power...

Just my 2p. Remember, we're not professionals!
BTW I'm in Farnham. If you want to limp it over here I'll have a look. I don't do house calls! I have timing gun, known good coil, known good 3-pin CDIs lying around.

Cheers, Richard.

[McQueen911]

Agreed, given that it ran fine and then sudddenly didn't, an igntion issue is the likely culprit. When you pulled the plugs to do the compression test, what was the burn like? If they're sooty, then your injectors are fine but you've got a weak spark and my guess would be your CDI has failed and it's just running on coil power only. Before investing in injector testing kit, I'd take Richard up on his offer, switch it out with a known good one and then see where you stand. Even if it's still Mini'ish, then at least you'll have ruled that out. Old school problem diagnostics is a process of elimination. Now days they plug it in and ask a computer what to do next.

Good luck, Dan

[Jonny Hart]

but you've got a weak spark and my guess would be your CDI has failed and it's just running on coil power only.
Good luck, Dan

CDI failure is an engine stop. It can’t run on ‘coil power only’ unless you rewired the harness.

I have seen points close by themselves and throw the timing out which would cause poor running.

[dogbower]

I’m no expert, but when we’re your rubber hoses last changed?
I had one that would collapse when being driven hard, opened back up when tootling along.
Stuart

[KS]

My Carrera 2.7 suddenly started running like crap at Brands Hatch PCGB sprint - looked everywhere and turned out to be that the points had closed up. The heel had worn away so they were not opening far enough – as the heel had worn away progressively, there was never a feeling that anything was wrong until the point came (excuse the pun!) when the points just wouldn't open to give a spark.

[johnM]

All of the advice is sound. All I would add is that I have had a MFI injector fail open on my car. It started to run on 5 cylinders. This was more obvious at low RPM with the engine under load, as you increased the revs it seemed to run a bit better.

You can clean injectors, ive used injector cleaner from Halfords and a work top injector tester pump to fire the cleaning fluids through the injector. Works very well.

Kind Regards

[2.4TE]

Thanks all for your input.

When I sent my plea for help, I was part way through 'Check, Measure, Adjust'

https://www.pbase.com/slidevalve911rsr/ ... _bosch_mfi

I'd aleady worked my way through to checking the ignition (dwell, timing), to no avail.

Anyway, I carried on, including a valve adjust for good 'measure'.

The plugs were very oily, I haven't changed them for quite a while and was waiting for the new ones to arrive.

I do like the idea of Jonny Hart's CDI wizadry https://www.classicretrofit.com/collect ... i-ignition

and wonder how much of an improvement it would make.

Fuel flow spot on.

I also removed and cleaned the air-correction screws and then resynchronised the throttle valves.

New plugs arrived and fitted.

Hey presto! Normal service resumed! Car runs nicely again.

After that slight deviation, back to plan A: getting some negative camber into my Clio 182 for the next autosolo....

So again, thank you all, and Richard (inaglasshouse), yes we should catch up since we're just down the road from each other. I'm planning on attending the (PCGB) early Porsche event at Goodwood Aug 17th:

https://www.porscheclubgb.com/events/20 ... t-goodwood

Anyone else?

Cheers,

Dave

[911hillclimber]

Good going, but why were the plugs oiled?
Had they been in the engine for a long time?

[2.4TE]

Good question: why were the plugs oiled?

Maybe I should have said they were very black, meaning not really 'wet oily', more 'sooty'.

So I checked my log of when I last changed them to answer your question. Yikes: 29/1/06 at 48972 miles, now at 56053 miles. So that's 7081 miles and over 13 years

I use Bosch W4CS. That's heat range 4. Maybe I need a slightly hotter plug to burn cleaner.

What do folk use?

Dave

[911hillclimber]

Ah..sooty and not wet oil.
Running rich or short runs etc.
I would use what the factory states.

[domtoni]

Hi Dave, long time no hear !!

I replaced my points with a Pertronix point set replacement. I had problems with the points closing (always had a small gap), and have been pleased with their results. Not an expensive replacement either so you might want to consider it.

Dom

[jtparr]

Thanks all for your input.

When I sent my plea for help, I was part way through 'Check, Measure, Adjust'

https://www.pbase.com/slidevalve911rsr/ ... _bosch_mfi

I'd aleady worked my way through to checking the ignition (dwell, timing), to no avail.

Anyway, I carried on, including a valve adjust for good 'measure'.

The plugs were very oily, I haven't changed them for quite a while and was waiting for the new ones to arrive.

I do like the idea of Jonny Hart's CDI wizadry https://www.classicretrofit.com/collect ... i-ignition

and wonder how much of an improvement it would make.

Fuel flow spot on.

I also removed and cleaned the air-correction screws and then resynchronised the throttle valves.

New plugs arrived and fitted.

Hey presto! Normal service resumed! Car runs nicely again.

After that slight deviation, back to plan A: getting some negative camber into my Clio 182 for the next autosolo....

So again, thank you all, and Richard (inaglasshouse), yes we should catch up since we're just down the road from each other. I'm planning on attending the (PCGB) early Porsche event at Goodwood Aug 17th:

https://www.porscheclubgb.com/events/20 ... t-goodwood

Anyone else?

Cheers,

Dave

August 17th sounds good....although I am no longer a member of PCGB....
I'm also based close to Guildford


all the best
Jonathan