Related to the Bowling & Grippo Fuel Injection system.
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Michael
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Still have 1600 rpm spikes!

Post by Michael »

I reckon I have all the anti rpm spike components in place - R10 set to 3.9K ohms and the various capacitors, and even a potentiometer in series between Bosch pin 1 and the MS rpm input pin and I'm still getting some wicked spikes at 1600 rpms's (seems pretty much confined to just this rpm):

http://www.alfagtv6.com/MegaSquirt/data ... 2005_1.zip

I have the pot set as high as possible ... to the point where the tach signal drops and the car sputters, then backed off a bit (you can see evidence of this in the log where the rpms drop slightly). The resistance on the pot is approx 22KOhms.
Can anyone recommend some way to finally fix the tach signal?

I tried installing the John Zenner diode (though Steve's write-up indicates its not needed - install the jumper instead) and it made no difference.

The car is running WB now without an AFM and in spite of the tach spikes, is running very well (even though I'm still using Steve's base map ... just set to WB).

How about going to the MegasquirtnSpark-extra? I read somewhere that the code interprets the rpm signal better. I wanted to avoid this added complexity until I was more experienced with tuning though...

Thanks!
Michael
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Post by Steve R »

OK, one last trick for you... it's a "trick" but I assure you it works. After doing the build I still had very occasional spikes, this gets around it :-

1/ Set one of your fuel table entries at 1600 rpm to correspond with your spike and make sure you're happy with the tune of all entries.. this can be done in several iterations as and when you want to.

2/ Set you're second last RPM entry to whatever the max rpm is for your engine (maybe plus a couple fo hundred rpm to allow for any rpm erros etc). Tune it as you need to.

3/ Set your very last rpm line at 100rpm past the line in section 2/ so that it's for RPM that you will never ACTUALLY see in reality.

4/ Copy all the exact same VE entries from your 1600 rpm line into your "non real" rpm line. If you change the 1600 ve figures, change the top line too.

5/ test drive and smile.

What this does is present the MS with a VE figure the same as the real VE figure for 1600 rpm in the circumstance that you get a spike. The MS might see 1600, 1600, 1600, 18100, 1600 in subsequent engine cycles but will provide the engine with the same size squirt of fuel in milliseconds in any case - result is you won't notice the rpm spike at all, other than when viewing datalogs.

I'm currently playing with later versions of the MS code and these have an option to average out high transient rpm spikes. I don't know exactly how it works, but it does work. I'll feedback more later, but for now I'm working with getting spark control running properly.

Hope that helps.
83' GTV6, 3.0 24v supercharged
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Michael
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Post by Michael »

Thanks Steve - that was very helpful and I changed my VE table as you suggested.
I had very few tach spikes ... but still the jerkiness at 1600+-. In looking at my setup, I realized that I had set the O2 correction to activate at 1700 rpms so now I'm wondering if its not so much the rpm spikes, as the sudden change in mixture as the O2 sensor's input is factored into the equation. I'll test again with the threshold set to 7000 rpm's (as you had it) and see if that helps.
More testing (tuning!) to follow this weekend :)

On a related topic, in using MS Visual Log Viewer, I noticed that my WB sensor is not easily supported - I have a Zeitronix.
It goes from 0.15V (9.7 AFR) to 3.27V (21.2 AFR) with 2.5V = 14.7 AFR. At least my switch point is correct. I guess I'll need to make my own table for MS Visual Log Viewer since I cannot make a correct one using the MS Visual Log Viewer TBLGEN.exe utility (it does not match all the V/AFR points so I assume the output from Zeitronix might not be linear :()

Cheers & thanks again,
Michael
1981 GTV6
David
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Post by David »

Michael,

I also have a slight stumble at 1600 - 1700 rpm. It is across a wide MAP range. My datalog shows no spikes but sometimes a drop to 800 rpm at that point. I've tried altering the VE table but it has no effect.
It's not a major issue as it doesn't occur under hard acceleration or normal driving. Just one of those littlle annoyances. Your comment on 1600 rpm+- caught my attention. I'm not yet convinced it's fuel related.

I tried opening your datalog but got a file corruption message.

I'll check my O2 activation rpm and try Steve's trick.

I'm about to install my second MS on my stock 2.5 GTV6 so will be interesting to see if the same issue occurs.

David
Last edited by David on Fri Feb 11, 2005 3:08 pm, edited 1 time in total.
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Post by Michael »

Hi David:
I'll post my results - interesting how similar our problems are at 1600/1700 rpms. I've also noted a slight dip in revs (in the log) at that point (to 800 rpms).

I must have uploaded the log file using the incorrect FTP protocol, I'll fix this as soon as I get home - I'd be interested to compare your log to mine.

Cheers,
Michael
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Post by Michael »

Michael
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Post by Michael »

David wrote: I also have a slight stumble at 1600 - 1700 rpm. It is across a wide MAP range. My datalog shows no spikes but sometimes a drop to 800 rpm at that point. I've tried altering the VE table but it has no effect.
It's not a major issue as it doesn't occur under hard acceleration or normal driving. Just one of those littlle annoyances. Your comment on 1600 rpm+- caught my attention. I'm not yet convinced it's fuel related.
Well, the VE changes did not solve the problem - still have this 1600 rpm stumble. I cant see any changes in VE or Pulse width in the log when the stumble happens, so I'm beginning to agree with David that its not fuel related. Could it be spark?

Cheers,
Michael
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Post by David »

Michael,

I opened the log ok. The stumble point is almost identical to mine. I see you get the drop to 800 rpm an an occasional spike upwards. I only get the drop to 800 rpm and also at exactly 1,600 rpm. If I'm reading the log correctly you also don't seem to get the problem when accelerating hard.

Maybe we should compare specs.

I'm running a stock 3.0L although it may have S cams if I can ever identify them.
Stock 2.5 distributor & coil.
No AFM
Stock 3.0L high Z injectors.

What have you set as the lowest rpm on your VE table?

David
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Post by Michael »

David wrote:Michael,

I opened the log ok. The stumble point is almost identical to mine. I see you get the drop to 800 rpm an an occasional spike upwards. I only get the drop to 800 rpm and also at exactly 1,600 rpm. If I'm reading the log correctly you also don't seem to get the problem when accelerating hard.

Maybe we should compare specs.

I'm running a stock 3.0L although it may have S cams if I can ever identify them.
Stock 2.5 distributor & coil.
No AFM
Stock 3.0L high Z injectors.

What have you set as the lowest rpm on your VE table?

David
Hi David:

We have very similar specs.
I have a 3.0 with a ported head and S cams.
Stock 3.0 dist and coil, but slightly modified spark box.
No AFM.
Stock (new) 3.0 liter injectors.

I hope to run some more test tonight - it really feels like a spark issue, and I was wondering if I can test this with a timing light...
Seems like an unlikely hypothesis, since it runs fine with LJet and the ignition is untouched. Still, it really feels like the flame is going out at that rpm.

Cheers,
Michael
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Post by Steve R »

I've been reading through all my own notes on this & hope the following comments might help a little. I also saw the same problem & the changed the components mentioned in my guide pretty much curing the problem for me. However....you've tried various resistances and buffering capacitors, plus the "VE entries" trick, which works on spikes, but not 800rpm "holes", unless your VE at 1600 & 800 are the same (unlikely). & you've found none of this cures it.... hmmm.

For what it's worth I also think it's ignition related, maybe a usually unnoticed misfire at that rpm, L'jet would ignore that as it simply relies on "load" from the AFM to allocate fuel whereas MS calculates MAP load x rpm x other factors. It could even be electrical noise from the alternator, I digress but someone on the MS forum with a BMW solved his problems with an alternator rebuild !

One test I considered but didn't get to do was running the car on L-jet, with the MS powered up and connected to the feed for rpm, then just datalogging from the MS. This would show if the problem is present with l-jet but well masked, or whether it's a specific MS problem.

At one point when practising trial and error to fine tune R10 I jumpered a 0-10k rotary pot in place of it so I could try different settings whilst driving, at the same time I'd already added the "dave" cap etc. I only got about 20 yards when the pot "sparked" as a adjusted it & the car died :shock: Pushed it back in the garage in annoyance etc !

Turns out I'd "blown up" the U4 opto isolator. Whilst sourcing a replacement I read the detailed spec of the 4n25 component and noticed it's more sensitive to heat when soldering than most - hence my note in the guide to solder this really cautiously.

Having changed U4 to a new one - carefully - all was well as 800 rpm tach holes had vanished, just the very occasional spike at 1600 - not enough to even notice unless viewing an extended datalog. Since then all have been fine on mine.

You could try changing U4, if you do, I suggest soldering in a 6 pin socket first (these are pennies), therefore avoiding any heat soak issues. I didn't add a socket, but would have if I'd thought of it at the time.

At the moment I'm playing with newer versions of code that have an option to "ignore false" entries - works perfectly.

I will update the guide for adding ignition control once it's all OK and will include other changes too. (for instance soldering sockets for U4 & U7 so they are easy to change if necessary)

hope thats of help
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Post by Michael »

I'll try a new U4 (OPTO ISOLATOR) - in running web searches, I have run into other people who solved similar problems by changing that component.
Do you know what the 6 pin socket part number is? I cant seem to find that information from Digikey - are they generic in that there is only one type of 6 pin socket?

How about switching to another type of ignition?
http://www.msdignition.com/ignition_4_6200.htm
I read that someone else with a GTV6 solved their rpm spike issues by switching to MSD...

Thanks,
Michael
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Post by Michael »

I found it:
http://home.earthlink.net/~jcgebhart/mspartnums.txt

AE7312-ND 0.46 Machine 6 pin socket for IC U4

Digikey was not too helpful - they just sent me the data sheet for the component.
Michael
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Post by Steve R »

They sell them at RS to...

www.rswww.com part number 813-109
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Post by David »

Michael, Steve,

When I did my MS assembly I used a 6 pin socket for U4. Also replaced the stock alternator with a reconditioned Mercedes 85 amp model.

What about a separate shielded wire for the tach signal?

I have an MSD ignition unit so it might be worth me hooking it temporarily and see what happens.
I might also slap a couple of suppressors around various wires as well.

David
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Post by Michael »

OK, good deal - I like the idea of a separate shielded cable - perhaps a microphone cable? I've heard that suggested in the MS forums.
By the way, have you cleaned your coil/amp connections as Peter suggested? I'm going to do that before the next run.

For my part, I have just got my MS converted to run MegasquirtnSpark-extra. Works well on the Stim - a bit of a chore setting up the exact version of Megatune and the correct msns-extra.ini ... with the correct S19 version and then re-entering all the settings and setting up the VE table. Apparently it deals with rpm fluctuations differently - we will see. I hope it solves the problem ... either way, I want to try out the target AFR since I have the WideBand installed already.

Cheers,
Michael
1981 GTV6
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