3.2 Carrera dead cylinders post top end rebuild

[ystarrev]

Hi, All,

It started first go and runs, but cylinders 1 and 2 are dead.

I have checked spark, spark plug wires to correct plugs, and have narrowed it to the fuel injection, I think.

At idle, pulling the injector plugs from 1 and 2 doesn't drop the RPM. Pulling any of the others (including 3) results in a drop in RPM.

I am concluding that perhaps there are 2 bad injectors? I'm going to pull them this evening, but wanted to share my experience in case anyone has any other thoughts.

One other surprise in my checking is that when I measure the voltage on all the injector connectors with the ignition on, both contacts are +12. This is on all of them, including the ones that are working properly.

Yves

[Nick Triesch]

I had the same problem on cylinder number one. I double checked the valve lash, then while covers were off I sprayed KB Blaster on valve adjustment areas of both exhaust and intake. Then I replaced number one fuel injector with a new unit . The last thing I did was to replace the spark with a slightly hotter spark plug. I started car and cylinder came alive!!! It was dead!!! The very first thing I did was check compression and number one was lower than the rest but still in spec.

[Nick Triesch]

BTW, I also had 12 volts at number one fuel injector.

[yelcab1]

With dead cylinders, the first thing you should do is check compression, leak down, then ignition and spark plug, then finally gas. It's somewhere in there.

[uwanna]

I developed a problem with my 964 3.6 motor. Had trouble on cold start,
but ran Aok when warmed up. Turns out to be a bad connection to the Cyl temp sensor in the large cammed connector block to the ECU. Sprayed DeOxit D5 on the the pins in the connector and ECU, problem fixed. Also had a bit of unstable idle and a bit of hesitation on part throttle. Sprayed all the
connector pins and seated the cammed connector several times, all problems gone! I guess after all the years the pin connections had developed some resistance. I know you have a 3.2, but same type connections. Give it a try, can't hurt. Also the injectors always have 12v,
the injector activates when the ECU applies ground to the injector.
DeOxit D5 is awesome stuff, removes any corrosion and protects from
further corrosion. Used to work in the electronics biz, and it was the go-to
contact cleaner.

[jamesjedi]

Originally Posted by yelcab1

With dead cylinders, the first thing you should do is check compression, leak down, then ignition and spark plug, then finally gas. It's somewhere in there.

The above is a great place to start.

[Flat6pac]

The injectors go to sleep when they haven’t run in a few weeks. On start up, if they’re not running give them a slight tap with a screw driver handle. That usually lights them off.
Bruce

[theiceman]

Originally Posted by yelcab1

With dead cylinders, the first thing you should do is check compression, leak down, then ignition and spark plug, then finally gas. It's somewhere in there.

with all due respect i disagree with this as will 99% of professional mechanics.

the first thing you check is spark , always, as its by far the most common cause and easiest to check. requires no tools. ( never mind the fact checking compression is not easy on horizontally opposed engines. ).

Then depending on fuel system could be as simple as pulling out an injector and putting in a jar to check fuel. if not. Then move to compression which will require a compression checker and removing a plug and cranking.

[jamesjedi]

I think the iceman is bringing up an important point, spark is easy to check. If the engine has sat for an extended period injectors can fail and need cleaning/testing.

However, this is a top end rebuild. These other items should be checked if the fault is not found.

[yelcab1]

Originally Posted by theiceman

with all due respect i disagree with this as will 99% of professional mechanics.

the first thing you check is spark , always, as its by far the most common cause and easiest to check. requires no tools. ( never mind the fact checking compression is not easy on horizontally opposed engines. ).

Then depending on fuel system could be as simple as pulling out an injector and putting in a jar to check fuel. if not. Then move to compression which will require a compression checker and removing a plug and cranking.

It's an 84 Carrera, you can do a compression test of that dead cylinder in 10 minutes. And what self respecting mechanic would NOT have a compression gauge that costs all of $35?

in fact when you do this kind of a job, before you put the engine back in, you hook up a battery to a starter and test its compression... as an extra measure of insurance.

[gtc]

Check the injector harness, especially at the tight bends.
When I rebuilt my engine at 375,000 miles, the injector harness sleeving and wire insulation had worn away in places, likely shorting out the injectors at times. It was not priviously visible, since the harness is normally zip tied to the fuel rails quite tightly.

['76 911S 3.0]

Originally Posted by gtc

Check the injector harness, especially at the tight bends.
When I rebuilt my engine at 375,000 miles, the injector harness sleeving and wire insulation had worn away in places, likely shorting out the injectors at times. It was not priviously visible, since the harness is normally zip tied to the fuel rails quite tightly.

Get a noid light and plug into cyl 1 and 2 injector connectors and see if it blinks while cranking. That will tell you if the injectors are being driven properly, eliminate that variable.

[john walker's workshop]

Tap the injectors several times with a small ball peen while it's running. Those injectors can stick after sitting dry for a while.

[ystarrev]

Thanks to all who chimed in. Noid light showed all was well, so I whacked the two injectors a couple times and all was perfection. Super satisfying to complete my first 911 R&R!

[theiceman]

Originally Posted by yelcab1

It's an 84 Carrera, you can do a compression test of that dead cylinder in 10 minutes. And what self respecting mechanic would NOT have a compression gauge that costs all of $35?

in fact when you do this kind of a job, before you put the engine back in, you hook up a battery to a starter and test its compression... as an extra measure of insurance.

agreed, but you can check spark in 5 seconds.
Also it was stated ALWAYS check compression first, I was giving a different perspective