1984 Carrera engine stutter
 

This stock 3.2 engine ran great until it developed a stutter after it warmed up a bit. The the stutter got worse and it actually died out once.

So I replaced the fuel filter, air filter, the DME relay, and the Head Temp. sensor. Ran okay again until it warmed up and the stutter came back.

What should be the next logical step?

Went thru almost the exact same thing, except I did not replace the fuel filter. Replaced DME relay and CHTS.

Then checked for Vacumn Leaks at usual 6 culprit points (no leaks), replaced faulty ICV then O2 Sensor for infrequent hunting issues at cold start now my baby runs perfect.

Also had PPI done and the inspector did a very scary thing. He punched the gas in 1st to 6.5-7RPMs and blew out a whole bunch of carbon evidence by a puff of grey smoke. She runs very smooth now.

My .02

Thanx for the reply. I actually bought a new O2 sensor but someone told me that it would not cause the issue of runing ragged after it heated up a bit.

About that IVC, don't want to sound any dumber than I really am...but exactly where is it located?

Thanks again.

Ignition, ignition...ignition!

What sort of shape are your spark plug wires, how many miles do you have on your injectors? Although with the car running well when cold - and running poor when warm points more towards the cht sensor. Did you replace that correctly? The new two wire version? Did you have issues installing it where you may have crimped or cut the connecting line

The plug wires and the distributor both look good. Not sure about the injectors. Would it only happen after it warmed up if that was the culprit? Also, once it begins to stutter/miss it seems to run normal (although way too fast!) if I keep the revs up above 4000 or so.

I did use the two prong version of the Head Temp sensor. I didn't have any problems getting it thru the firewall or screwing it into the head.

Could you be more specific?

It starts up excellent even after it had sat for over a month in sometimes sub zero weather.

Also, would an ignition issue not usually get worse at higher RPM? It is doing just the opposite. When the stutter/miss begins it will run almost normal if I keep the revs above 4000.

Fuel injection, fuel injection, fuel injection!

Did I mention fuel injection? :D

I ran through similar issues several years ago. My rough running was intermittent at best. Hot, cold, different rpm's, etc. I swapped out parts from good running 3.2's, and also replaced numerous parts to no avail. It ended up being 2 bad injectors. I went ahead and replaced all 6, and the car never ran better! Also picked up better fuel economy as well. Injectors don't last forever, and mine were in piss poor condition after 20 years and 130k miles! There are services that will rebuild them and bench flow test them for much less than new OEM. I had little choice, as at the time this was my daily driver, and it would have taken some time to get them serviced.

engine stutter sounds like what happens when you get a little water inside the distributor cap. The contacts ground out and you get some cross firing.

I don't know why your problem seems to be heat related.

If it were my car, I'd pull the distirbutor cap, and check for dirty contacts, clean out all of the dust that could be transmitting spark, change the rotor if necessary, and then run the car in the dark. Look for evidence of arcing. If you see a lightshow, then you've found your problem.

Next I'd buy the Bentley manual for the 3.2 911. Go through the diagnostic steps for the Motronic components. No need to go out and throw parts at it until you've tested the components with a multimeter. The cht should be tested at various temperatures to make sure it is functioning within spec. It's really easy to do if you have the right tools.

It's possible the connection to one or two injectors is bad too, or could be a faulty injector. But I'd suspect it would run badly at all temps in that case. Maybe you have a loose intake plenum mounting bolt that is letting in air when the engine heats up.

Did yours run very good at initial startup...mine does...and then begin the stutter/miss after 5-10 miles? I also goes away if I keep the revs above 4000.

A buddy just told me today that since I have to replace the DME relay and the Head Temp. sensor that a "5 gas" guage/analyzer will probably be required.

What the hell is that?

Also, when I was replacing the engine sound/heat shield I did remove the fuel injection intake plumbing. But it's pretty straightforward and simple to get back on correctly and I doubt the stutter/miss would only happen after it ran a few miles.

Do a leak down test on all cyclinders just to see if there are any internal problems. I had a customers car in my shop 3 years ago with similar problems you disscrib turns out a mouse had built a nest ontop of the #6 cyclinder and caused it to overheat. It lost compression on #6 when it got warm and would stall and shutter. The end result was a top end rebuild

I will check the distributor and cap next. I actually have a new one on hand.

I did the inspection in the dark thing and didn't see anything.

Most of the time, it ran absolutely PERFECT on startup. The problem RPM would always fluctuate. Once I got past the problem RPM, it would run great. No rhyme or reason to ambient temp, oil temp, length of time running , etc. I suppose you can always try a couple of bottles of Techron. If it's just a minor FI clog, it might take care of it. Considering how old these 3.2's are, and how many miles are on them, it couldn't hurt to have your FI's overhauled. Do this, and your car will run better as well as getter better fuel MPG. Search for a local vendor, and it might run $30-40 a piece. Especially if your car is not a daily driver. It would be a tremendous help if you had a local Pelican with whom you could swap known working components from before throwing a bunch of money at this. Another item to check is the actual DME Computer. If you can swap yours out from a friends, you could eliminate this component. I do remember reading where a similar problem was isolated to a few bad solder joints in the DME causing similar symptoms... the "search" function is your friend!

I'd buy the Bentley Manual.

I know I'm repeating myself, but the diagnostic section is great, and you'll end up using it over and over anyway.

If you like books, there is a book on Bosch Fuel Injection and engine management in the books section of this website. I bought it many years ago, and it has paid for itself many times over.

Actually, one of my kids sent me the online version of the Bentley manual but it's not so easy to navigate. I'll take a look at it.

Is it happening under load? It may be a clutch issue.

No, I thought about that the first time it did it as I was pulling away from a stop sign. But it continued to do it intermittently even when cruising along in 5th gear so I doubt that it's clutch related.

Looks are meaningless. How old?

Not sure. Gonna get into that today maybe.