jonfkaminsky

Hi all-
I've been noticing that my car has been running erratically lately, especially noticable when hot. I've checked the dist. belts - no problem. Valve adjustment - okay. I did notice a regular clicking in the motor compartment that sounded awefully electrical in nature, but can't be sure. My symptoms are as follows:
1. Occasional low pickup
2. Pinging sound on part throttle acceleration, especially under load (uphill) but ONLY when engine hot (at least to mark at 8-9 o'clock on temp gauge), and outside temp. is hot.
3. Occasional surging on acceleration, mostly again when hot.

I performed the check fault code procedure and received the following:

One long, pause
one short, pause
two short, pause
three short, pause
four short, pause
(sequence repeats itself from here).

This translates in my thinking to 1234, which would indicate a Hall sensor fault(?). I've read that this may not be indicative of anything other than a "red herring", but on the other hand, it may indicate some spark getting to ground somewhere. I've also read somewhere that the absence of a proper Hall signal can retard ignition timing. In any case, might this be responsible for the drivability symptoms, in the case anyway, that I have translated the engine light sequence correctly?

Thanks in advance for any help on this.

Jon

Fred, Long Island

If you search this board for my "Ghost" problems last year, there are a host of replies that mentioned this.
My particular problem turned out to be a fried DME unit. The rebuilder was sure it was caused by a grounded plug wire. He insisted I replace them. Did so and it's fine so far.

J-McDonald

My car also had some "ghost in the machine" issues, which manifested themselves in "limp mode" driving and intermittent flashing of all of the dash warning lights. It recorded a hall sensor error, but it ended up being a corroded coil wire. Someone else on this board had the same symptoms, with the same ultimate problem - bad coil wire. FWIW, the coil wire was A LOT cheaper than the hall sensor.

Adrian

Dear Jon,
If the hall sensor has failed you cannot start the engine. I think it is a red herring. The hall sensor detects TDC of #1 cylinder. Without this input the DME cannot do anything and it will shut itself off.
I would be looking at the cylinder head temp sensor. This signal from this sensor plays a critical role in timing.
I have helped somebody offline with a slighlty different problem but what we have found is the reasonance valve is playing up. The solenoid is okay but the vacuum section is kaput. Took a while to find the problem though.
Heavily oil contaminated and some other fluid which we are trying to work out what it is.
If this valve fails and stays open between idle and 5500 rpm it causes havoc with running. Intermittant badly fluctuating idle was the original problem. Loss of power when driving along and hard to start sometimes.
Ciao,
Adrian
911C4

GMS

We have a 964 c4 with a similar problem here.
Could not get into diagnosis system with hammer and found out car has aftermarket chip. Swapped over DME unit with "known good" one and problem solved. Check all grounds and ignition wiring first.

Adrian; Any 964 will start with the hall sensor wire disconnected. The "hall sensor" fault code often comes up on the hammer, even if there is no problem.

Adrian

Dear GMS,
Well I ain't going to argue with you. The 1989 Carrera 4 Porsche manual clearly state that it will not and I am not going to try it. I will defer to the manuals when I advise people.
Ciao,
Adrian
911C4

AndrewM

When the Hall sensor fault code showed up on my C4 it turned out to be a bad coil. Unplug one ignitor and try to start the car on one coil, then reconnect and try the same thing with the other coil. Car should start on either one... Hope this helps.
Drew
89 C4
86 930

914und993

Hall sensor fault code on my C4, along with episodes of really bad lurching, missing, and stalls. Turned out to be carbon tracking in a distributor cap. All was OK after the caps were replaced.

Chip

Bill Wagner

Jon:

Code 1234 is for the Hall signal generated by the distributor. The second digit (2) implies an erratic (non-constant) error, but had it been 1124 it would have been a constant failure.

If the DME is telling you the truth, I would look for loose/intermittent connections anywhere in the distributor area. The previous poster sounds like a good example of what could cause this as well.

CHEERS

jonfkaminsky

Thanks guys- Will do a complete check this weekend if I can get some time off my remodeling project.

Ade - C4 91

Adrian,

You mentioned the Reasonance Valve. Where is it located?

Ade

jonfkaminsky

Finally went through everything and could not find anything obviously wrong. In desperation, I pulled the chip and replaced with stock. And....problem solved, no pinging in the afternoon heat. So now the question remains, would the mapping in this chip result cause pinging (unless I have bad knock sensors)?

So my theory is now that there is still something wrong with my car - knock sensors, cylinder head temp sensor, intake air sensor, or possibly a faulty evaporative emission control system. I suspect these as possibilities because of temperature dependencies and this problem only occurs when it is hot outside and I reach the 8-9 o'clock mark on the temp gauge. My car is lean and mean in the morning and a pinging puss in the afternoon.

Perhaps the aggressive spark advance mapped into the chip coupled with the above possible problems may have conspired to cause the issue. I can't believe it would be the chip alone because if it were, the knock sensors should have caught it but they didn't. It is supposed to be 95 deg tomorrow so if this thing is going to ping with the stock chip it will do so tomorrow.

I'll call Paul at Cyntex tomorrow and see what he says.

BTW, anyone know where the test points on the cylinder head temp sensor are? I have a chart of test temps and resistance, but don't have any idea where the test points are.

Thanks
Jon

Adrian

Dear Ade,
The resonance valve is part of the throttle body assembly. It sits between the two air intake halves. You will see a solenoid, a vacuum line and a linkage assembly. To get to the valve itself which is a butterfly valve inside a length of pipe you have to remove the intake assembly and pull it appart. Not a huge job and quite an interesting road to discovery.
Ciao,
Adrian
911C4

jonfkaminsky

95 degrees outside today and car ran good all day with absolutely no pinging. Paul wasn't available at Cyntex today so will try monday.

Lorenfb

Could it be that the knock sensors were disabled
to allow max. performance?

Have to love those performance chips.

Good luck
Loren
Systemsc.com