Well after a hard few weeks of trying to get two cars ready for the GAF event we are happy to say we made it, both 914 3.2L conversation cars rolled out the door for some fun with others. It was great to meet up with so many new and old friends from the 914club and friends from my racing days with POC.
On one car we know the history and had run the motor so we know everything about it, the other was a purchase that not even the seller could give much info about the motor. But after hours of hard work we got both cars running and running pretty good, Except for one problem that leads me to this question.
On my friends car the injector had clogged or gummed up from setting and all 6 had to be changed out, this made it run and idel pretty good but at 3500 –4000 rpms under load it has a steady hesitation or miss. We have tried all of the following with new or known good parts with no success at fixing the problem. And when you come to a stop it will die if you don’t catch it by giving it a little gas. Up to 3500 or so it runs strong. After 4200 rpms it run good. Turn the key let it sit it idels fine.

Changed ECU
Idel air meter
ECU relay
New fuel pump
Mass air flow meter
All wires checked about 3.5 ohms
New plugs cap and rotor.
Checked Grds and connection
Fuel pressure at 30-PSI average
Valve adj, done.
Changed out Coil

The next two items is the Throttle position sensor, and the Reference sensor.
Question; On the flywheel from Kennedy Engineering When the pulley & rotor are pointing to TDC the single pin that the Reference Sensor reads is about Two inches over from TDC, Should this matter?
Any tips from you guys on fixing the hesitation would help out. Thanks for the time.

My 3.2 also has a minor stumble at about 3k RPM. I traced it to a slightly faulty MAF which I've decided to ignore for the time being.

I also had a problem with the engine dying after closing the throttle. I found that I'd switched the connections for the ISCV and TPS. Surprisingly the engine still ran like that but wouldn't return to idle. Have a look at yours or just switch the connectors to see what happens.

Later,
Kevin

Thanks Kevin we will check that. What is the ISCV?

If you haven't already guessed ISCV = Idle Stabilization Control Valve.

It is a stubby yellow can with a hose in and a hose out that bypasses the throttle valve and stabilizes the idle.

What John said!

In a 914 installation it's towards the front of the engine, top, more or less mounted on the centerline, widthwise, of the engine. It looks like a small electric motor which is what it is more or less.

If switching the connectors doesn't do it there are some troubleshooting procedures for it (ISCV) in the Bentley manual.

Later,
Kevin

Any tips on the stumble at 4K rpms?

In my case it's the MAF (AFM I think is more correct in this case). If you test the AFM with a power supply hooked up and a meter you may find a "dead spot" or two along the sweep of the metering flap. Basically its a reostat that gets worn out in specific locations. There is a pretty good troubleshooting/test write up here. You'll notice that this is for a 944, however, at this level the AFMs are all the same between the motronic 944 and motronic carrera. Using the procedures outlined in that link I was unable to make any improvements to my 3k stumble. But at least I know what's causing it and if I ever run across a deal on a AFM I'll buy it.

Later,
Kevin

There are alot of things that can cause your problem. From wires to the Idle control valve.
Before I bought my 3.2 motor I researched it on Pelican. Mulitple things can cause the same hesitation problems.
Check this link out, its a search on carrera and hesitation. You can see alot of the different fixes 3.2 owners have tried.

3.2 hesitation link on pelican

I should also say not all the threads are for hesitation so you will have to weed them out.

The other motor we are running runs perfect so we switched out the AFM and it made no dif,.

Is your stumble repeatable in the shop (with the car parked) or is the stumble only under load/partial load?

Is it worse under full throttle or partial throttle?

My street car seems to have an intermittant light stumble somewhere between 3-4k, but only after it has warmed up and only under part throttle. I haven't yet been able to pin it down. (I can't repeat it with my car parked in my shop.)

I'm leaning toward one of the two crank sensors (probably not the reference sensor since the car starts up fine). Mine however, has no problem returning to idle.

Have you run your car in the dark and watched the plug wires for arcing? (In the dark, you would be able to see the blue arc if they are arcing.)

I have not yet opened up my AFM, but have read that article and may try that sometime down the road.

Please keep us posted.

This motronic 3.2 stumble seems to be very prevalent. My stumble is also at partial throttle settings. Wide open it pulls right through the 3k zone with no hesitation.

I electrically troubleshot all the motronic system sensors (hot and cold) as well as the fuel system. I wasn't able to observe the reference sensors while the engine was running because I don't have a scope at home. Everything checked within the electrical specs from Bentley except the for the AFM which I mentioned in an earlier post. I did check the crank sensor to crank pin clearance and found one of mine slightly closer than it should have been and corrected that but it didn't make any difference in the stumble or anything else.


Hey John, how come you are leaning towards the crank sensors?

Regards,
Kevin

Yes we have run the car in the dark to look for arcing none seen. And ohms on all wires checkes out at 3.5.
As the car is parked yes you can feel a little miss as it sits and idles.

I'm leaning toward crank sensors as I have also troubleshot most of the other sensors and all so far seem good. I don't have a functioning scope to check the signals from those crank sensors either, but reading on Pelican BBS, several (with a somewhat similar stumble) have had good luck when replacing the 20+ year old crank sensors . They are expensive, so I may just try one (not the reference sensor).

My other thought on mine was crossfire, but I didn't see any sparks between plug wires in the dark either.

I have not fully checked out my AFM (which may be part to blame), but right now mine is intermittant enough for me to live with. (It does seem logical that the tracks of the AFM would be worn in a particular spot after 20+ years of part throttle cruising day in and day out.)

I cannot seem to duplicate my slight hesitation while parked.

Have you checked the injectors flowrate and spray patterns?

I suppose as a last resort, you could swap the ECU for a known good one to make sure that isn't at fault somehow. (I have heard stranger things)

Swaped ECU and have checked the flow rate on injectors There new, no luck.

Jeepers,

You have changed out just about everything. How about a flakey Cylinder head temp sensor?

Well we just put in a new 02 sensor matched to the ECU. The old one was a single wire and the new one is a two wire, seems to make to diff,. also put in a new head temp sensor. Still same problem. Next is to try and test Speed sensor. We are almost out of ideas.

Did you try the speed sensor yet?

Since you've changed out so much stuff and proll'y spent over 1K doing so, did you consider just having the shop plug into your diagnostic output plug for a readout ?
The dealer will charge approx +-$200.00 for the diagnostic readout, usually the first piece of business with the DME motronic 3.2.
My worst motronic gremlin was the mechanism below the rotor in the distributor, which just wore out and hung up. The engine ran great for awhile--then like crap.
Check it out.
Marty

This may sound silly but since you did change the fuel pump, are you sure that the hoses to the pump are not mixed up. ie. in - out - and return.
Just an idea.

I have all the parts in a running car so there was only the cost of the fuel pump, which was needed for convertion anyway, the head temp sensor and the 02 sensor, always a good change anyway. After we do the speed sensor change. Maybe I will have to take it to the Dealer if that dose not fix the problem. Never have needed to in all my years but this one is a real workout.

Never hurts to check again thanks.

I'm curious how the dealer would "plug" this car in.

It is pre-OBDII being a 84-89 engine.

Is there an in-line Motronic Tester of some sort?

Curious minds want to know.

The only "test" ports that I am aware of on the 84-89 DME cars are the 3-pin round plug that is a third crank sensor, and the relay looking plug that when jumpered allows the base idle speed to be set (it disables the idle stabilizer).

It would be convienant if these cars would have had OBD-I.

Johnman I am with you is there another way to plug this car in? that three pin I see but is there something I can check from that port?

Any updates or progress toward getting your 3.2 running right?

Thanks for asking Johnman. Well I learned a little lesson on this one. The person that I was helping on the conversation did all the basics, cap. Rotor. Valve adjustment , cleaned oil screens etc. and did a very good job with all except for one thing. He did not tighten the little tips that screw on to the top of each plug. Not until I said lets go old school did we find the problem, I had remembered in the past feeling this kind of problem with cars that are carbureted. That would mean fuel or ignition, We Refited all plugs, cleaned and re-gap them. Now the car runs great. I learned that when you are working with others check each other work from time to time, you never know. In my racing days I never let anyone help on my car, it was my life out there and if I am going to go it will be for what I have done.
We spent 5 hrs looking checking and swapping parts but we learned a lot and feel more comfortable with many aspects of the 3.2MFI. The funny thing is we both didn’t care that it came back to something so simple. We just where happy that it was running so great A 3.2L in a 914 will always put a smile on your face.