2.7 suddenly running on 5 cylinders

Patronus · 10-24-2002, 01:40 AM

My '74 2.7S ran perfectly and smoothly, but this morning when I started it up it backifired and seemed to have lost cylinder no.4 overnight.

Last night when I parked the car, it was perfect. This morning I woke up to a different car - one that only has 5 cylinders and backfires visciously above 3000rpm.

I haven't checked the compression but when I pull the plug wire from cylinder no. 4 there seems to be no response, indicating that the problem lies there. I also put a different spark plug in, no difference. There is indeed spark on wire no.4, I checked.

There is no blow-by or blow-out sound before and after firing up the car, in other words, no preliminary indication of a pulled head stud or otherwise loose cylinder head.

Background: The car was stationary for about a month, and yesterday I drove it for the first time. I drove it a few hours during the day, and also once or twice last night. The car never became hot, and was a real joy until I parked it for the night.

Could the fact that it had been standing for a month anything to do with the problem?

I have decided not to drive it today.

What can it be?

Siena911 · 10-24-2002, 05:23 AM

Patronus,

Sorry, I can't help but, thats what happens when you bring a new Girlfriend into the garage. The 2.7 is probably just grumpy

Congrats on the new Carrera btw.

Cheers Jakes

ps. What do Carrera's go for nowadays in SA? Are there many in the market, and what are the insurance premiums like? You can pm me if you like.

I never looked into it when I was there, but I thinking about it the other day.

Rot 911 · 10-24-2002, 05:29 AM

What do you need for ignition? Fuel, air compression and spark. You have spark. Pull the injector and see if you are getting fuel. If you are then I suspect no compression. Considering this problem just happened, most likely the intake and/or exhaust valves managed to find their way out of adjustment.

724doorE · 10-24-2002, 05:58 AM

might check for loose/moved rocker shafts on that cyl.

Chuck Moreland · 10-24-2002, 06:14 AM

What did the spark plug look like on #4? Fuel fouled? If it isn't firing it should have fuel on it. No fuel on the plug suggests the injector is a problem.

Pull the injector out, put it in a jar to catch the spray. Crank the engine and see if you are getting fuel. Is the spray pattern good?

Compression doesn't just dissapear overnight. You have a fuel or ignition problem.

Early_S_Man · 10-24-2002, 06:51 AM

Check the #4 spark plug wire for end-to-end resistance. If it is open, you need to test the Beru connector after unscrewing it from the wire. 3000 Ohms +/- 10% is the usual spec, though some later ones are 4000 Ohms.

The CDI unit can sometimes jump across the gap of an open connector, but a used spark plug is a different 'kind' of load than an open-air gap for test purposes!

Patronus · 10-24-2002, 12:52 PM

Thanks guys, I didn't expect so much attention!

Update: I enriched the mixture on the fuel distributor (quite a bit) just to see what would happen, and voila. Running on 6 cylinders now, and no backfiring. The problem thus seems to be fuel-delivery-related.

Superman · 10-24-2002, 01:52 PM

Well then I strongly suggest you put the injectors in jars, turn on the key and raise the sensor plate. Observe the spray pattern. Then measure the volumes. Switch injectors around and repeat. To see if it is an injector problem or a FD problem or what.

Adam · Adam's Garage

The 2.7 gremlins must have been working overtime last night!

I drove mine around all day yesterday and it ran beautifully. I parked it and then took it out after dinner and it kept stalling at the lights. As you'd slow to a stop, depress the clutch, it'd stall.

Anyhow, I drove a long in 2nd gear for a while, to keep the revs up (Bill Cosby's "Clear out the gunk"

) and once it got upto 180ºF/80ºC, the problem cured itself. I'm wondering if it'll do it again this morning...

Back on topic, I had the same problem about 2 months ago. It turned out to be bad injectors. The car had just clicked over 100k miles and I'd let the car sit for about 3 weeks. So when I started it, it was rough, smoky and a bastard to drive. New injectors, valve adjustment and it's truckin' again!