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Something is pulling back ignition timing, not knock sensor


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34 replies to this topic

#26 grossgary

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Posted 21 December 2012 - 08:52 AM

same intake manifold through all the issues? those are easy enough to swap might be worth a shot.

i've seen 88-91 XT6's have wiring warn through and the metal is exposed or a wire is infiltrated with green corrosion and both can create wildly erratic symptoms. fixed one last week - green corrosion at least a foot up the wiring loom past the connector. 1 or 2 times out of 10 they won't show a check engine light for some reason. the one i fixed last week never had a check engine light but was nearly undrivable. the green corrosion the car would drive fine, then not...drive, buck, stumble...then take off like a rocket...and somehow even when it was nearly undrivable, couldn't pull an incline it would have no check engine light. that's actually fairly common on XT6's for one wire in particular, i've seen it multiple times so I was able to work around it fairly quick and get my friends car home.

I have never seen it in a newer gen car but they're aging to the point where it might be possible?

#27 Fairtax4me

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Posted 26 December 2012 - 11:47 PM

No news. Haven't done anything to it lately, haven't noticed it doing anything wrong either though. Thought it might have been acting up the other night but figured it was probably because I was riding around with 3 friends in the car. An extra 600 lbs makes a difference in how these things move. :lol:

Wiring doesn't seem to be an issue on this car for the most part. The only corrosion I've ever really found was on the battery cables. I made sure to get the wire harness tucked out of the way when I put the intake manifold back on last time. This problem has been occurring since long before I did any major work to this car though. I was thinking the other day about how far back I can remember this being an issue, and honestly I think it's been there since I bought the car. I remember there being some minor random losses of power, usually when trying to accelerate uphill, just a few weeks or months after I bought it. Which makes it even more strange that whatever is causing it hasn't completely failed by now. :confused:

#28 presslab

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Posted 27 December 2012 - 01:42 AM

The only way I could figure that you're seeing timing that far off is if the ECU is confused as to the engine RPM and therefore pulling your timing from the wrong spot in the map. Maybe your 97 is completely different than my 92 map but I'd guess not. I couldn't find a ROM for a 97 online to look at and I figure you have an OBD2 cable, and not a SSM1 cable, and can't download it.

Have you tried looking at the RPM from the scanner to see if it jives with your actual engine RPM? I guess now that it's not acting up it will be impossible to diagnose. Anyway cam/crank sensors still come to mind. They're just coils of wire, and the wire could have an intermittent open/short.

Did you backprobe the connectors? That's ok, but poking things into the front side can damage the terminals creating an intermittent connection; I figure you know this but just checking.

#29 Fairtax4me

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Posted 27 December 2012 - 04:28 PM

RPM is one of the parameters I look at the most while driving around. I make sure to keep that on the scanner along with spark advance, TPS %, MAP, MAF, and Load %, and sometimes ECT or O2 sensor voltage or fuel trims.
Haven't noticed any anomalies with the RPM reading, but ill keep an extra eye on that next time I notice it acting up.

Don't have an SSM1 cable, but I've been looking around for a good setup. (Cable and software) Building a cable myself isn't a problem, and seems like it would be much cheaper than buying the evoscan cable for $50+. I'm just not sure which type exactly I need to build.
Obd2 car with a 97 ECU, should be Ssm1 right? Any advice?

My buddy with the o-scope knows a lot more about electronics than I do (some of the stuff I've read about all this might as well be Greek) so I'm going to enlist his help with some of this.

Connectors were back-probed. I did have to pop the sockets out of the Crank sensor connector because the rubber boots were hard as rocks. Pulled them out and put them back in the connector with paper clips wedged against the back of the crimps at the end of the socket. Hooked up the scope and started the engine, ran it for about 5 minutes at varying RPM, then took it all off. must have deformed the sockets slightly and didn't quite make a good connection after I put them back because the engine wouldn't start and I got codes for the crank sensor. Pulled them back out and made an attempt at tightening them up a bit. Not sure if that had an effect but the engine did at least start after that.
I got codes for that immediately though, and it didn't even pretend to start. If there was a loose connection there before I don't see how it could affect the signal without setting a code.

#30 grossgary

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Posted 27 December 2012 - 09:47 PM

You already swapped injectors right?

I don't see how it could affect the signal without setting a code.

I've seen pre-OBDII knock sensor, coolant temperature sensor, MAF and crank sensor failures (rough running and no starts) without throwing a code.

OBDII stuff is more robust but I don't think it's immune. Though nothing other than cylinder misfires comes to mind that I have seen. Currently looking into a friends EJ25 that misfires with no CEL, though occasionally it will trip, but usually not. I think it happened once on another EJ25, but the other was a few years ago and my memory is fuzzy, swapping intake manifolds fixed that one.

I always wondered how a signal could be so corrupt to leave a car undrivable, or nearly undrivable, without setting a code.

#31 presslab

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Posted 28 December 2012 - 02:35 PM

Don't have an SSM1 cable, but I've been looking around for a good setup. (Cable and software) Building a cable myself isn't a problem, and seems like it would be much cheaper than buying the evoscan cable for $50+. I'm just not sure which type exactly I need to build.
Obd2 car with a 97 ECU, should be Ssm1 right? Any advice?


Yes I believe SSM1 was used through 1998. I built my SSM1 cable with a Scosche Su02B radio harness and a FTDI cable TTL-232RG-VSW5V-WE, like described here:
http://www.4bc.org/vanagon/engine.html

The newer FTDI cable I used is nice; it has LEDs for TX/RX, but it's $21. There is a cheaper FTDI setup here, although the free shipping can take a month.
http://dx.com/p/ftdi...wc-black-142041

I pretty much use JECScan software for dumping/general memory access, and EvoScan for logging SSM1 along with WBo2.

#32 Fairtax4me

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Posted 28 December 2012 - 06:43 PM

Injectors have not been swapped. Though I suppose I could try my spare set, I don't think anything is wrong with the current ones.

Looking at pictures of the SSM1 plug I remembered seeing a similar plug under the dash of my car. Sure enough there's a yellow 9 pin plug with 4 wires in the right places. I'm trying to figure out if the wires go to the right places on the ECU, but the I/O pinouts I can find for the ECU don't show anything about the SSM plug.

Presslab thanks a ton for the links. I've been to tinkering with the idea for a long time to hook up a laptop in the car, but haven't found the right resources and info to do it. I'm looking forward to getting this put together now.

Attached Files


Edited by Fairtax4me, 28 December 2012 - 06:50 PM.


#33 grossgary

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Posted 29 December 2012 - 09:41 AM

Not interested in swapping your spare intake manifold on it? It would have to fix the issue and they're easy? new wire, new sensors, fuel rail/injectors, and you already replaced the ECU. the only thing left would be the body side wiring harness. if you wanted an exercise in problem solving you can try to track it down off the car.

if you replace everything, it's hard to not fix it.

#34 Fairtax4me

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Posted 03 January 2013 - 01:46 PM

I may swap the manifold just for giggles sometime. I'd really like to know the actual cause though. If I move everything with the manifold it's harder to know just what's faulty.

After riding around for about a week now with my false knock sensor plugged in I have noticed a small increase in power overall, and an occasional ping here and there, but I still get periods of random power loss. Since I can't seem to make the problem happen on a consistent basis I'm just going to swap out one part at a time and drive a week in between to see if there is any noticeable difference. If I stick to that schedule, I should have every sensor/electrical part changed out by about March. :-p

#35 grossgary

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Posted 03 January 2013 - 02:07 PM

I may swap the manifold just for giggles sometime. I'd really like to know the actual cause though.

that's what i figured. wish i knew what caused the one i fixed by swapping manifolds.

I'm just going to swap out one part at a time and drive a week in between to see if there is any noticeable difference. If I stick to that schedule, I should have every sensor/electrical part changed out by about March. :-p

HA HA!! :headbang:




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