Carrera 3.2 stutter/misfire/surging on car with MAF conversion

[tmaull]

Yeah, you could toss it. Sal Carceller has a sweet MAF kit. I have one, and I’d buy it again in a heartbeat. Does the autothority kit have a pitot tube or a hot wire?

[TimNiceBut]

Originally Posted by john walker's workshop

Autothority MAF in the round file. Old technology. Put that airflow meter back on.

I would in a heartbeat if I had one. Unfortunately the car didn't come with any of the parts that were taken off by whoever did the conversion.

If I can't trace the running issues to other factors, I will try to find all the necessary parts. I'm not a big fan of this conversion for various reasons, like pulling in air from the hottest part of the engine bay.

Originally Posted by tmaull

Yeah, you could toss it. Sal Carceller has a sweet MAF kit. I have one, and I’d buy it again in a heartbeat. Does the autothority kit have a pitot tube or a hot wire?

It does look it is hot wire, but that weird tube arrangement doesn't quite fit my mental model of how a hot wire MAF works.

I'm not exactly wedded to a MAF conversion (my last C3.2 didn't have one and ran much better than this thing) but I'm also aware of how the old AFMs are wearing out.

[tratza]

Keep the MAF versus the original "barn Door." I have well over 150,000 miles on mine. Exhaust always passed the Houston air test without the cat until NOx was tested. Works great with the 964 grind cams and dual out exhaust. Autothority chip came with the MAF. With the original the engine doesn't run near as well. Only failure which was hard to track down was the potentiometer began failing. The engine would suddenly quit for a couple seconds or more but always started back up. $90 later and back on the road. No symptoms like your 911 though.

[TimNiceBut]

In between fixing up stuff the local motorcycle dealer touched, trying to get out of the house for a bit and emergency repairs to the roof of my shop, not much has happened.

I did clean some more electrical contacts, rechecked the distributor cap and noticed the contacts in the cap look slightly "burned", but nothing similar on the rotor. Either way, no damage in there so I put everything back together. Then cleaned up the contacts in the front fuse box with some electrical contact cleaner, basically starting carefully before going to more abrasive methods of cleaning. Oh, and for my amusement I unplugged the NB O2 sensor.

Result - it still pops a bit at cold idle, but while the oil temperature is in the lower white zone and a bit above, it runs almost perfect. Pulls up our driveway in 2nd gear at 2k rpm with no fuss (which is has never done before). Looks like dumping in more fuel because it went to a safe map helped. Of course I had to explore this a bit more and took it for a longer drive. The more the engine bay heated up (keep in mind the cone filter is in exactly the wrong spot and the heater elbow in the engine bay isn't hooked up right now), the more it ran like it used to. This culminated in driving up towards our house and getting misfires again in third gear around 3k-ish. But even with that, it does run a lot better with the O2 disconnected. Nevertheless, heat is a definitive factor here, which also explains why it ran noticeably better when I originally got the car in January. I'm still wondering if the MAF conversion did away with the intake temp sensor and the ECU now just assumes a random temperature.

The plan for now is two swap out the plug leads as they are of an indeterminate age and I have a set already, even if I don't like the fitment. Oh, and hook up the heater elbow again to keep some hot air out of the engine bay. Depending on the outcome of that I may have to test the fuel pressure and also look at the battery voltage while driving.

[TimNiceBut]

Originally Posted by tratza

Keep the MAF versus the original "barn Door." I have well over 150,000 miles on mine. Exhaust always passed the Houston air test without the cat until NOx was tested. Works great with the 964 grind cams and dual out exhaust. Autothority chip came with the MAF. With the original the engine doesn't run near as well. Only failure which was hard to track down was the potentiometer began failing. The engine would suddenly quit for a couple seconds or more but always started back up. $90 later and back on the road. No symptoms like your 911 though.

Thanks for the tip regarding the potentiometer. I wouldn't be surprised if that's slowly giving up the ghost on my car as well.

I'm definitely also planning to check the DME and open it up to verify that it's got the correct chip in it. My main annoyance right now is that I can't see what the ECU is seeing, which makes it hard for me to validate some of the theories I have. I suspect that aftermarket engine management might still be in the car's future.

If I do keep the existing MAF conversion I'll still have to figure a way to move the air filter to a place where it has a better chance of getting cooler air.

[tmaull]

While you have the DME open, check that non of the solder has cracked. Sometimes it needs a reflow.

[TimNiceBut]

Thanks - I was planning to do that and check for the typical kinds of "old computer damage".

[stlrj]

Meanwhile you might continue trying to source a used AFM or see if you can borrow one in order to continue your process of elimination. If the symptoms continue, it may have nothing to do with the MAF system.

[TimNiceBut]

Originally Posted by stlrj

Meanwhile you might continue trying to source a used AFM or see if you can borrow one in order to continue your process of elimination. If the symptoms continue, it may have nothing to do with the MAF system.

That's definitely part of the plan. Currently I'm working down the list of items that I already have, but in absence of a smoking gun I'll probably swap back to the original AFM and airbox.

The whole thing is beginning to feel like it's a combination of issues, not a single big one.

[wrxnofx]

Former Autothority MAF 3.2 Carrera user here.

Garbage, along with that dumb cone filter thing. Stomp on the throttle and you'd get a whistle out of the engine bay. Take the cap off the oil tank, no difference in idle. Thing was creating a vacuum leak (i.e. lean condition) somehow.

The PO at least had the decency to retain the original chip he had taken out of the DME. I tracked down a stock airbox and AFM on this site for a few hundred dollars. Those, a couple brackets, gaskets, rubber buffers, swap the chip back, and all is right with the world. Runs way better as a stock setup.

I tried to sell the Autothority setup on here. Shockingly, no one wanted it.

I just saw an airbox up for sale on here recently. Put out a WTB on the AFM if you want one.

BTW - you said you checked the coil. Did you check it while it was hot (i.e. during the poor engine running condition) or at room temp? For as garbage as that Autothority thing is, I never had the driveability issues you suffer.

[stlrj]

Originally Posted by TimNiceBut

The whole thing is beginning to feel like it's a combination of issues, not a single big one.

Take a deep breath because it's usually just one simple issue. No reason to make it more complicated.

[TimNiceBut]

Originally Posted by wrxnofx

BTW - you said you checked the coil. Did you check it while it was hot (i.e. during the poor engine running condition) or at room temp? For as garbage as that Autothority thing is, I never had the driveability issues you suffer.

Thanks for your insights re the Autothority MAF - I still remain unimpressed with it.

I did measure the coil cold. That said, until I disconnected the O2 sensor, the "misfires" (quotes because I'm not sure that's what they are) started immediately, but did get worse. I'll try to remember to test the coil again when it's hot to see if I get any substantial difference in resistance.

[TimNiceBut]

Originally Posted by stlrj

Take a deep breath because it's usually just one simple issue. No reason to make it more complicated.

That's what I'm hoping it is, which is why I'm systematically trying to eliminate issues. Unfortunately I have a justified reputation of running into "funny, I never saw that part go wrong" type problems. And yes, that's an actual quote from a mechanic .

[scarceller]

Install a Wide Band O2 gauge, with this type of gauge you will know EXACTLY what your air fuel ratio is at all times. I suspect you are running lean in the problem areas. The AEM 30-4110 is a good gauge for the money.

If you send me an email sal.carceller@cox.net I'd be happy to send you a sheet I created for gathering 7 test cases with AFR numbers. But you must have a WideBand O2 gauge!

[danco_]

I have a 3.2 Carrera with Autothority MAF still installed and working wonderfully. The trick in my case, was to get Steve Wong to custom tune for this MAF as Autothority's tuning was utter dog ****. Once Steve blessed me with his tune, the car ran better and harder than it ever has. I'm at 215whp with a US 3.2 and it runs SWEET.

As for your symptoms, I had something quite similar. Turns out it was a wire or two from the Engine Loom that was not contacting the MAF's plugs consistently. The engine loom connectors were coming out of the plug and not making good contact with the MAF, and creating all kinds of surging problems. My mechanic tested EVERYTHING and when he went back to the very basics and checked connections, he found this to be the problem. He had everything fixed in 20 minutes once he isolated the issue.

Car runs great again. The MAF is a good upgrade if you have the supporting engine tune.

Good Luck.