Chrome v2 - Limp mode at 3000 rpm?

Hi Everyone

I've been struggling with a problem for at least a year now, and I've finally given up on diagnosing it myself. I've also received a notice that it's time for a technical inspection in mid-December. The technical inspection is pretty serious here in Switzerland, and I don't think I will make it through in its current state.

It sounds exactly like this: http://www.3sgto.org/turbo-engines-s...e-stumped.html
That car randomly fixed itself, so that thread didn't help me other than to at least know I am not the only one :(

I would really appreciate it if you guys could offer some advice. Details below.

Car: 1995 VR4
Relevant Mods: Chrome v2, ECU from Brett, 750cc injectors, Pampena short block with forged internals, Aeromotive FPR
Any other mods shouldn't really be relevant to this problem.

Problem:
Driving with low load and not much throttle, in any gear, as soon as it hits ~3000 rpms the ECU drops the timing advance to like 5 deg. This causes it to run terribly, of course, and it gets stuck in this error mode until I rev it up to ~5000 rpms in neutral with full throttle. Sometimes, it is so bad that I can't get it over 3000 rpms anymore at all. In that case, I am stuck with < 3000 because it drives pretty normal below that. If I disconnect the battery for 10 mins, it clears out this error mode and works fine until the next occurrence.

It does not happen with WOT, and also not with the MAF disconnected. I think it only happens in closed-loop mode.
Today I made a datalog that clearly shows the problem happening. I have basically all fields in the log that could be somehow relevant. See attachments for log file and graph.

Some things that are definitely going on:
- The knock sensor gets into a fault condition and outputs a constant knock sum value. This is configurable in Chrome, so I have changed it to 0 for the constant value and it doesn't help. The knock voltage looks ok, however. Also knock base and knock sum until that point are fine. I have played with knock settings to make it less sensitive to noise, but didn't have any luck.
- The octane flag goes from 100% to 0%. I have tried to disable the octane/knock logic in chrome, but I think that caused other problems. Could have been my tune at the time, though. I will try that again.
- The timing advance drops to something between 0 and 8 degrees or so.


Some things I have replaced already:
Fuel pump
Fuel filter
Fuel pressure regulator
Diaphragm in FPR
Injectors
Injector wiring harnesses
Changed my FP hotwire setup to also include the FP resistor like stock, in order to prevent overrun.
FP relays
Air filter
*Special* boost control solenoid, but that is disabled until very high load. Also tried stock and just running disconnected.
BOV
Intake piping
Knock sensor
Knock sensor wiring (close to the sensor at least)
Fixed most boost leaks
Idle stepper motor
Throttle position sensor
Throttle body seals and adjustment screw
Spark plugs
Spark plug wires
Measure coil resistances, looks ok
PTU is fairly new, but I still have the old one. I will try that also.

At this point, I am thinking of swapping my stock injectors back in and trying the stock ECU. If that doesn't work, I still have my MegaSquirt I guess...

Thanks for any help you can offer!
DavidC (aka VBBlckBelt)

Edit: terrible image quality on the graph for some reason. Here it is on imgur: http://imgur.com/QBogw5R
Attachment 8551Attachment 8552

I believe it's a wiring or hardware issue with the ecu. I remember in some of my early testing with flash ecu's(way before chrome) I had this happen. It only happened with some of the sohc ecu's that I converted. I suggest contacting the manufacturer of your ecu and having them test it on a test bench.

Thanks for the advice, donniekak. I can pretty much confirm your guess now.

- I put my stock injectors back in and copied the stock fuel settings into my current tune, and the problem was still there.
- I then put my original ECU back in, problem gone!
- I stopped at a gas station and put my Chrome ECU back in and started from the plain Chrome v2 binary. I turned off the peripheries for secondary O2 and whatnot, as in my other tune, and the problem was still there.
- I stopped at a rest stop and put the original ECU back in, problem gone again!

I believe it must be something with the knock sensor hardware, because I datalogged again while using the Chrome ECU and I had knock sums of 9, indicating knock sensor failure. Is there some known problem with knock sensors and the clone ECUs?

Anyway, I am stuck with my original equipment for now, but I will probably pass the inspection. What a relief! :triumphant:

My Chrome ECU is from THE ORIGINAL VR4 Clone? ECU | Custom Clone, Clone² and Universal Clone ECUs for 3000GTs
I will try to contact him and see what can be done.
I believe it has not worked properly from the beginning, but I always assumed it was some other problem since I was changing other things at the same time.
If I had known I would have this much trouble, I probably would have just stuck with MegaSquirt :-/

That is exactly what was going on with some of the ecu's I tested, at first I thought it was the conversion harness I made, but other ecu's worked fine. I never looked into it much as this was before chrome and it was easier to get 98-99 ecu's.

Keep us posted on how this goes. Hopefully you'll be able to replace your Chrome ECU with a working one from Brett without any hassle.

Definitely a problem with the knock sensor circuit. I had the same problems, even posted in the thread you linked. Could be in the ECU or in the wiring between the sensor and the ECU. I had the problem with multiple ECUs so my issue had to be in the wiring. I took it apart and tested everything and it was all good, so I put it back together and it has worked since then. I must have had a loose connection somewhere (my most likely guess would be where the sensor wiring plugs into the main harness near the plenum). It's possible its your ECU so if you can get it checked, do it.

Could also be an issue with the wireharness adapter too.

Thanks everyone. I suspect it's not something under the hood, because I can swap out only the ecu and it changes the result every time.

What's weird is I do get a signal on the knock sensor. Seems realistic to me as well, but I don't have much experience with diagnosing the oem knock sensors.

I will take a look at the harness adapter this week sometime. I did check the O2 sensor orientations there, but I didn't think about checking the knock sensor.

I haven't received a response from his gmail address. Does someone know another way to contact him? Please pm me if so.

I would normally wait a bit longer, but I am visiting the US soon and it would be most convenient to take care of this during that visit if possible.

Mine did the same thing, bad knock sensor circuit in the ECU. Have to send it in for repair.

Same problem at one point and it was the knock sensor. They are definitely worth changing if you haven't replaced it yet.

https://3swarehouse.com/product/oem-...nsor-md159216/

Talked to Brett at cloneecu, he did not receive your email so try again.

To the OP

Did this get sorted?

I also have a Chrome ECU v2 and a very similar problem is happening.
Fault condition at 3500rpm or over and pulls timing back to 5 deg and goes into Limp mode.

I'll swap my stock ECU back in and see if I have this occur. At least narrow down what the cause might be.

Are these all na flash ecu's that have been converted to run on turbo cars?.

I've had it with SL ECUs and full VR4 clones.

Dougal, log your knock voltage and knock sum and see if that is the source of your problem.

Yeah ive logged heaps and knock voltage bounces around between 0 volts and 0.02 or 0.04 or 0.08.
Knock base kinda of follows the movement of the knock voltage.

Is knock voltage supposed to be higher? Like closer to 5 volts normally?

the bouncing around of the knock voltage on my logs does not seem to correlate to which I suddenly get 9 counts of knock.
The only constant is being over 3000rpm with increasing load during acceleration.

Im truly hoping its just my knock sensor failing in that despite being time consuming to get it out and replaced is easier than it being something ecu related.

Think I just found an answer to the above question. Looks like my knock sensor voltage into the ECU is way way low. Should be higher within 5 volts.

I have either a knock sensor fault or wiring to the ecu from the knock sensor is faulty.

I'll probe the harness from the ecu back to the plug on the intake plenum to rule out the wiring part.

Quote:

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Originally Posted by Dougal

Is knock voltage supposed to be higher? Like closer to 5 volts normally?

---

No....

So a normally operating Knock sensor is ok still ok if its 0.02 - 0.08 volts?

Whats normal?

Here is my knock sensor values (log count, voltage and knock base)

Is this example of a likely faulty sensor?

Need some direction here if you can help.Attachment 8632

Looking at just the knock sensor tells me nothing.

What you're seeing is engine noise. The engine gets louder the higher you rev it. The engine gets louder the more air you push thru it.

If you're seeing 5V all the time, there's an issue as it should be quiet at idle and louder at redline WOT. If you're maxing the sensor at 5V then you're making some serious power! Like 700+hp! ....or you're really hurting your engine....

Basically.... I don't think the issue is your knock sensor.

Hey Greg,

Cheers for the reply.
I replaced the knock sensor anyway as the old one had cracks in and the lead was fraying wiring at its connection to the sensor itself.
It was cheap enough to swap over and just put my mind at ease.

New sensor shows a better signal but like you say is still low voltage as engine noise.

Still getting knock counts to 9 counts at 3000-3500rpm and over and it pulls timing to 5 degrees and CEL.

I don't really think its real knock but aside from using knock ears or a knock box im not sure how I can tell.

I have a tuner here in Sydney Australia who is pretty good with Mitsubishi EVOs and VR4 Galants and Legnums who I have asked to help.

I can only do so much with my limited knowledge. Thanks

Your knock voltage will be close to zero when you're idling, but it should come up when you're on the throttle. Looking at one of my logs I saw knock voltage up to around 1.5 volts during a 3rd gear pull. Yours may not be that high as my car makes 600whp, but if it's staying at less than .1 volts I think you may have a wiring issue or potentially a problem in the ECU. Make sure you log a decent range of throttle positions and rpms though. My hunch is you have a short or a bad ground in the wiring for the sensor. Have you tried cleaning the connection between the knock sensor and the wiring harness up by the throttle body? I think that connection is where my problems stemmed from when I had the same symptoms.

Greg, do you think issues like these, since they seem to be cropping up fairly common, could be related to the hullabaloo about the knock sensor circuits being different between the legitimate VR4 ECUs and the SL ECUs or potentially the clone ECUs? I know you generally think it's not knock sensor related, but in my experience that's the only solution I could come up with. You're much more knowledgeable about the intricacies of the ECUs and code though, which is why I'm curious about your experience.

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Purely anecdotal story, but I've been trying to sort a 'knock' issue as well.

I have a '92 TT, 13Cs, DP, LCDBC, 98 SL ECU/flash - very basic setup.

Prior to switching ECUs, my rebuilt-by-Seth TT ECU would show knock under low RPM low-/no-load conditions; particularly while shifting - usually 3-8 counts, but occasionally maxing out at 28.

I figured this for an anomaly, considering the conditions in which it would occur - it literally would not knock under load or during a pull.

I figured when I had the opportunity I'd replace the sensor and poke around.

In the meantime, I've gone Chrome, w/99 ROM, and the car runs better than ever, but it seems to run a bit richer (not over-rich); when I coast downhill, etc., the old exhaust 'crackle' is gone, and I can't make the damn thing knock - where the LCDBC would report knock previously, it no longer does.

I'm at a loss to explain this; I'd have some logs to post, but as luck would have it, my China knock-off Tactrix took a shit, and any further info will come in the spring (car is parked for winter), when I install RC550s, a Supra pump and Innovate WBO2.

I will have replaced the Tactrix as well - have to flash for the injectors - and will commence logging, hoping to get to the bottom of things.

I'll replace the knock sensor at that time, too.

I would start by swapping the into a different car. If the problem follows the ecu, then you know the cause.