2.7 is limping...
 

I have a problem with the engine in my 911.

It all started during a spirited drive, during which I might have rev'd it a bit too much... perhaps to around 6800 or so. I later discovered that the limiter in the rotor is (now was) 7300.

It was at the end of a long drive, so the engine was surely at normal operating temp.

Anyway, it seems like it does not run on one cylinder.

I then changed sparkplugs (all looked identical - black, but this could be caused by a few out/in of the garage drives) the wires, the distributor top and the rotor (6500 limiter).

This did not solve the problem.

I then took the spark plug wires off the spark plugs one at the time, and each and every one changed the idle for the worse in the same way.
So I guess this rules out an ignition problem...

Next is to check compression, I bought a tester today, and will test saturday.

As a side note, I should mention, that I adjusted the valves in the autum. And at the same time, I tested if the cylinder head nuts would tighten (sign of pulled studs). Most of them could I tighten with ease.... So a rebuild is planned, but I'd rather not do it now, when it's freezing outside. And workspace in the garage is occupied by an other car beeing worked on for the next month or two.

Have I missed anything? Any ideas? Suggestions?

possibly an injector or fuel distributor. remove the injectors keep them hooked up to the lines. test the flow rate and pattern of the spray. be careful of the potential fire hazard. i like to use small mason jars. take off the air cleaner lift the fuel distributor sensor plate and watch for an erratic pattern or lack of fuel. all injectors should spray about the same amount.

Ok, thanks, I'll try that.
Testing the flow rate might not be so easy - but as long as some fuel comes out and the spray pattern looks identical, it should be ok?

Easy why to check the injector is to tap on it with a wrench or something, I had problems with one or two of mine doing that in the past You are talking about mechanical injectors aren't you?

Yes its the stock CIS.

Tapping on the injectors?? What happens then?

if the engine is missing that bad and it's the injector or fd you will see the problem. also check for vacuum leaks. i use brake clean spray the injector holders while it is idling and in the area of the intake. if you have a sudden jump in idle or a smoothing out you will know that you found a leak.

Nice trick with the brake cleaner...!

The limping/missing is very evident when revving it, so that should rule out a vacuum leak right?

not if it's a bad induction leak. the engine will skip like it has a ignition problem.

Just to clarify: Such a leak would be between the meassuring plate and the cylinder heads right?

Pressure is what opens the injector, They sometimes get a flake of dirt and the stick shut after they set. By tapping on it (not hard) will free it up

just to clarify something.

1. you said that when you pull a plug wire off every cylinder dropped the same?

2. so if they dropped the same then all cylinders are firring equally. so you already know you have fuel and spark.

3. is the motor shaking? or just making a missing noise I.E. compression leaking from one of the cylinders?

4. is the miss fire load related under power. a weak coil or crack in the cap can cause strange things to happen.

good luck ill check back here later.

ed

could be many different places. intake gaskets, rubber boots on the air box, injector seals. vacuum lines, throttle body, cold start valve seal etc...

1. yes, the same
2. I guess so, but perhaps not enough to run more than at idle
3. not really shaking, and there's no obvious "pfft pfft pfft" as from a leaking head gasket
4. It could be load related. During the short distance I drove with this problem, the car did not pull well. It idles OK, but revving it clearly brings out the limping.

Thanks for your suggestions!

well if it idels good and doesnt pull as hard when is the last time you changed the fuel filter?

sounding fuel related

remove air filter and see if the throttle plate moves up smoothly it may be hanging up.

car off and key off as well.

ed

The strange thing is, that the problem started while driving and did not come creeping over a long time. I suppose a blocked(ish) fuel filter would not be good one day and bad the next..?

I'll check the sensorplate.

brake cleaner can have bad effects on rubber, like the O rings on the injectors. it will make them swell.

you said most of the head studs you could tighten with ease?????

what year car is it, 74?

did it backfire at any point? check poppoff valve if installed and make sure it is closed/seated properly

does it run rough when you accelerate or rev it up to about 4 or 5k and then run smooth if you hold it there?

could it be something with the advance in the dizzy.

you did say it idles fine?

OK, I'll take it easy with the brake cleaner.

Yes, 1974 model.

Yes, I could tighten most of the cylinder head nuts with ease. So I tightend them some, but not a lot. My tourque wrench was at my brothers at the time.

It never backfired. And there is a pop-off valve installed. I'll check it.

Well the rough running is most evident when revving it. I didn't really try to keep the rpm at a certain highish level.

It idles ok, but it could perhaps be better... not sure.

Don't use brake cleaner, its too harsh. I use spray choke/carb cleaner or starting fluid, these were made for the induction system.

I have a 74 2.7 and your problem is either (as everyone has mentioned) plugs or injection. You should pull the plugs and touch them to the case and have someone turn over the engine and see if you are getting a good spark on all the plugs. Then do the fuel injector flow test, its very easy and will tell you a lot about whats going on with your CIS.

are you sure you didn't bend the rockers on the over rev? these engines are very susceptible to this. do a leakdown to verify.

OK, I'll use diesel start spray instead.

I doubt its a bent rocker, after all, the same rockers are in the Euro Carrera, that has a redline at 7300... and it was surely not over 7000.

But I guess I'll know tomorrow.

Thanks for all your input. SmileWavy