Car misfiring, random misfire code, constant knock counts, oh my.

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Originally Posted by Toni

If I recall Greg has told me the RPM the ecu uses is from the CAS. Actually, a few months back I had a crazy RPM signal and car ran funny but a bit different than this. That's when he told me about it. I'm betting that was the first sign of the PTU going whack on me.

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Nope if he said that it was wrong. The CAS on the 91/92 provides the crank angle and TDC not rpm. RPM has always been from the PTU.

Well one of you is right that's all I know lol :)

Well, looks like there were two simultaneous issues :( The misfiring and the knock counts.

(For those that may not know, Chrome ecu can light the check engine light on knock counts. Mine is configured for 6. So my 7-9 counts I am getting make the check engine light go on)

Started up the car in the morning and went out about a mile. Knock light came on and the car felt like it had no power. Then it just goes away and the car comes alive.

The misfiring was happening with more frequency and I only saw this knock light issue twice. Three times now.

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Originally Posted by HellBringer

...In my experience, the ECS computer going bad is likely to take the ECU with it shortly thereafter.

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I fear you may be right and this may have already done damage even though it may not have been connected to my misfiring :(

7-9 Knock count is the sensor failing...

Yeah, or the wiring is shitty, or....the ecu has some gremlins.

Car lasted for like 17 years with it's first sensor and the second goes bad within a couple? lol. Possible though.

Mine was bad out of the box.

Wahhhhat? Really? Would prefer not to spend 100 bones again haha.

Yeah. It was the aftermarket brand one that Ninja sold. He took them off the site after 2 failed new.

Oh, well, tough to compare that to a new oem that has been working. Had me worried that I'd get a bricked oem one.

Hey Toni, sorry it took me so long to post here but the topic of the RPM signal coming into the ECU from the PTU got me second guessing somethings. It's just been so long since I did this that my memory isn't as sharp as it was on the various functions.

At any rate, the RPM signal does come from the crank sensor. Maybe the earlier cars did things differently but with the flash ECU, the crank sensor is what is used to calculate RPM. There is a math function which simply takes the crank pulses and divides them by 3 to get RPM. Its actually a bit more complicated than that but don't feel like writing a novel on my phone about it.

As for the PTU RPM signal input into the flash ecu, there isn't one. The output goes to the tach.

The ECU uses the crank signal pulses to time when to ground the PTU so it knows when to switch coils.