mr_bock

My 1996 Supercharged (TPC) 993 is throwing Cylinder 1 Misfire code. Once cleared, it comes back in less than a mile of driving, same code over and over. I recently replaced all of the ignition parts: coil, rotors, caps, wires, plugs because I was getting what felt like a stall when slowing to a stop. The car runs smooth now and does not want to stall. The distributor belt was replaced maybe ten years ago.

My question is what device detects the misfire and how can it tell which cylinder has the misfire. I want to understand this process and try and decide if this is a phantom misfire or a real ignition function problem.

Right now I have a piece of black tape over the CEL because it is annoying. It also sometimes flashing, other times it is just on.

Thanks!!!!!!!

wallra

the ECM is detecting the misfire. It know's the firing order and what cylinder is skipping. I see you have an 96 this means OBD2 so with a scan tool you could see the misfire and try changing that plug first and see If the misfire follows the plug. you could also see fuel trims to see If your running lean when the light is flashing that's when your misfiring and could hurt your converter

pp000830

Not sure which method below our car's ECU uses to detect a misfire, but I am sure someone will chime in on this:

1.)When a cylinder fires, it gives a kick to the crankshaft causing a slight variation in crankshaft rotation speed. The ECU has sensors that tell it the position of the crankshaft, from which it knows which cylinder should be firing next. When an ignition happens as it should, that's the power stroke and it gives a little kick to the crankshaft causing a slight increase in the RPM. The ECU sensors can tell it the crank position closely enough that it detects that slight increase.

2.) An engine misfire can also be detected by looking at the coil voltage just after the plug is fired.When the fuel/air mixture actually ignites there are lots of ions and radicals floating around.This provides lower measured resistance in ohms for electricity from the coil.
If the mixture does not ignite for any reason the resistance is extremely high.

pp000830

A flashing CEL is serious and its cause should be addressed immediately and before running the car further. A leaking fuel injector flooding the cylinder?

wallra

Its using the crank sensor.

mr_bock

Thanks for the information wallra and pp000830 !!!

I will have to read up on my scan tool documentation so I can perform the tests properly. I have the Durametric Diagnostic program and EASE Scan Tool X3.
The good thing is the cylinder 1 spark plugs are on the driver's side and easier to access!
I hope to sort this out this week.

The fuel injectors were checked, cleaned, and calibrated about two years ago, but something could have gone bad.
When the engine/trans were out about two years ago, I went through great pains to get the crank sensor into the proper gap position per the spec.

Lorenfb

Correct, i.e. the DME ECM monitors the change in the RPM via the crank sensor.

Correct, i.e. the DME ECM uses the Hall Sensor in the distributor to determine which cylinder just fired.

mr_bock

From the suggestions given, I put together a plan to sort this out. This morning I pulled both spark plugs from number 1 cylinder. They looked brand new with no color from ignition. I then pulled the lower number 2 spark plug for comparison and there was a difference. So... is it no spark or no fuel? I looked at the number fuel injector and did not see the electrical connector in place. After looking deeper with a light I see the connector buried under other cables under the fuel rail!!!! How about that!!!!! Without the input, I would most likely still scratching my head trying to figure this out!!!!!!!!!!!!!!!!! Thanks wallra and pp000830 !!!!!!!!!!!!!!!!!

Over the last three months, I had been working to fix the supercharger drive belt alignment (was making noise and you could see the misalignment). I probably had removed the connector and then forgot all about it. I guess I am getting too old for this hobby (will be 70 come this December).

With the previous codes erased, I took the 993 out for a test drive. WOW, what a difference a missing cylinder made along with a full tune up!!!!!! Smooth, strong that pulls very well up to redline!!!!! Best of all, No Codes!!!!!!!!!!!!!!!!!!!

Having Rennlist and the People here who share their knowledge is Fantastic!!!!!!!!!!!!!!!!!!!!!!!!!!

wallra

thank god it was easy. thats why you always go back and check the basics.

mr_bock

So true, easy to miss the details while looking at the forest.

I am so happy with how this supercharged (almost 400 hp at the crank) 993 is running!!! I know she's happy firing on all cylinders now!!!!!!!!!!!!!!!!!!!!

Now I have to watch my speed and stay out of trouble....

wallra

yeah I had a supercharged vw jetta vr6 315 hp my wife made me sell it because see said I was racing everyone. It wasn't me it when the heard the wine they always wanted to race. last time I got stoped was for 120 in a 50 and I was let go with no ticket but then the car had to go. man I miss that ride!

mr_bock

Ahhhhh, sweet memories.... lucky you did not get a ticket or worse.

nine9six

mr_ bock,
I would strongly urge you to purchase a decent generic OBD2 diagnostic tester.
I have an older Actron CP9580 that works quite well.

mr_bock

I have and used four different OBD2 diagnostic testers trying to figure this code. They all reported Misfire Number 1 Cylinder, nothing more. I downloaded the user manuals, but there is little info on how/where to dig deeper. I am no expert in any shape or form on the many parameters that some of these tools present.

Any suggestions on where to learn more. I would need very detailed instructions on what to look at and what is the meaning of what I am looking at.

Thanks!!!!

wallra

you need a scan tool that can read data. but the tool can only tell you what the car ecm can. a car that old sometimes can't tell you much with data.