Gen7 log...RPM related....

[ski_dwn_it]

Guys.

I have been running this gen7 for about 1 month now and have shared with norbs and some other the data I am seeing with my logs. The RPMs seem to be very jagged....is this what other logs from you guys look like too?

My car runs mid 10s nearly every pass 3000+ DA weather, N/A...doesn't miss a beat going down the strip and runs within a few .001 nearly every run, through the 1/4 mile intervals, when you break them down.

However these logs for RPMs SUCK. As you can see the output seems to be indicating that the RPMs are surging, but the car is smooth as silk going down the track.

If you look at the very end of the log, there are 3 peaks. If you scroll through that section - from peak to valley is a 600 RPM difference! In other words the RPMs while they should be climbing, are going up, then back down according to the logs.

I have a pretty loose converter on this car, its an 8" race converter 4800-5000 stall speed.

The sample rate for the log is set at 10 frames/sec....which shouldn't be too much I wouldn't think.

Can someone send me a log of their car through the 1/4 so I can compare.

If what is happening in these logs is truely happening, then I may have a problem somewhere.

I should also add that I have seen this same sorta RPM reporting when using my stock ECM, and logging runs on it last year. Do you think its in the distributer?

Any thoughts...I guess the main thing is do you guys seem similiar traces of your RPMs through the GEN7 as this?

 

[turbobuick]

Mine doesn't look like that. Are you coming to Quaker this weekend?

 

[ski_dwn_it]

That is not good... Can you send me one of yours...so I can see what it should look like.....

Being that I am now begining to think that I am going to be on a search and destroy mission to figure this out, not sure about this weekend.

What day is it again? Saturday or Sunday....

I have a guys distributer that I am building a 434CI motor for, and I am going to ask him if I can use his distributer to see if the logs straighten out when I use his....which will replace many of the items that could be causing the problem.

If that doesn't fix it, then things could get expensive. Being that the trans and converter are different, that means if the problems goes back to the Stock ECM readings weird like that, then its not one of those two items.

I think its going to be distributer related. How exactly does the ECM pickup the RPMs? It has a pickup module in the bottom of the distributer right....???

Thanks..

 

[TurboTR]

Just curious here- do you have a mag (inductive) pickup crank sensor? If so, are you 100% the polarity is right on the sensor wires?

TurboTR

 

[norbs]

Ski, i don't have any 3rd gear logs handy just some short blasts, but the rpm trace is smooth, not saw toothed. I think your tranny is slipping under full power partially.

 

[turbobuick]

I sent you a log from a dyno pull. Send it to Norbs he's been asking for one also. It is with the Accell brick and not the LM-1

 

[Scott231]

Something's buggered up. A slipping trans will show a drastic increase in the slope of the RPM line...not recurring peaks and valleys.

You are correct that it has to do with the RPM signal - that is being reported by the ECU. If you have a crank sensor mounted at the crank (no sh|t Sherlock) then you could have it mis-adjusted or a bad connection. The Fubar crank signal is causing the bad reading (the red line) through the ECU, however, the distributor is, assumably, installed correctly and is firing the plugs at the right time...making a smooth running engine.

I was surprised to see that you are not recording ignition advance. That might be interesting to see if it correlates to the RPM changes.

My $0000.02 anyway.

 

[aDFIguy]

I was surprised to see that you are not recording ignition advance. That might be interesting to see if it correlates to the RPM changes.

That's a great point. However, the ECM will report whatever it's programmed to do as far as the timing goes... It is seeing the RPMs changing, so it will change the timing as programmed. You'd have to be measuring the actual timing at the balancer to see if it's still tracking the programmed timing when the RPM fluctuations happen.

What are you currently using for a distributor? What type of signal (VRS, Hall Effect...)? Engine Speed is a function of the crank input signal and time... nothing else, no filtering or anything like that. What you see is literally what you are getting on the crank sensor input line. This sort of looks like a VR sensor wired backwards.

 

[ski_dwn_it]

Guys...thanks for all the input and comments and logs that were sent.

Yeah based on the log that was sent, I have a major problem....

My ignition is a stock HEI large cap distributer, with an MSD 6al. Its nothing fancy and has about 80k miles on it, so I am thinking it may be shot or just has some bad components in her.

I have a different one that I can throw in there and will try to do that tonight maybe to see if the logs smooth out.

By the looks of how rough my RPM log is, there might be some more ET there on the table to be had when this gets straightened out.....

Aside from the distributer is there anything else that could be causing it as far as the signal goes? In other words, if I pull out the distributer, and put the other one in, I should be eliminating a bunch of the possible things that could cause this. no?

While we are on the subject....how exactly does the signal get generated for the stock distributer? Does it go off a magnetic pickup in the base of the distributer........

 

[TurboTR]

Originally posted by aDFIguy
...
This sort of looks like a VR sensor wired backwards.

That's what I was wondering as well...

TurboTR

 

[ski_dwn_it]

Ok guys here is an update....

Last night I replaced my distributer with that of another one...and double checked all the connections...did not see anything that was obvoius...

I took the car out and made some passes with it, and the RPMs are still very spikey.

I spoke with a buddy of mine, that is VERY good with cars and he said if the trans was slipping or the converter was not working right, you would "feel" that much RPM change.

He thinks its software related, and false reporting. This led me to wondering if my laptop is fast enough. I know that DFI requests a 400+ mHz computer and mine is not quite that fast...around 300 and some mHz. Could that be the problem? I have a friends much quicker laptop that I can try and see if that helps...aside from that - the only other things I can think of doing is disconnect the MSD6AL and see if that might be flaking out or causing a problem.

Is there any way it could be a grounding problem? I have an extra ground coming off the battery, and all my other stuff seems to work fine. To me I would think that a 600 RPM drop that quick, could feel like a bucking bronco if it were truely reducing the RPMs that much instant to instant....

One last thing I am going to do tomorrow is take the car out with my father and have him watch the tach and see if its fluctuating like the logs show. If it is, then its really happening- if not then it has to be false reporting....at that point I am going to be clueless as to why. Could it be getting RF interference causing noise to be reported? I have the DFI box about 1/2 ft above the MSD box, which are both right above the battery....

 

[norbs]

lose the msd box.I never had one work properly yet!

 

[aDFIguy]

Separate the DFI and MSD boxes IMMEDIATELY and try a different ignition box if you can get your hands another unit.

One sign of a bad (or soon to be bad) MSD box is that it sprays electromagnetic noise all over the place. I have seen the noise from a failing MSD be extreme enough to corrupt the engine speed signal on more than one dyno DAQ system. It's possible that this could be causing the ECM to see some false edges on your crank signal input, not to mention that some of the data messages going to the PC from your ECM could also be corrupted by the noise.

 

[ski_dwn_it]

Here is another update....thanks a bunch for the help guys this is starting to drive me nuts.

Here are the things I have tried so far, and the car definately has a miss, which I can now hear....I took the roof off the car and its much more noticable now. You can't feel the miss, and with a helmet on and windows up you would be hard pressed to hear it. It only happens above 4500 RPMs.

I did the following this weekend..in seperate stages and tested inbetween:

A. Change out the distributer. - No change
B. Unhooked the MSD and connected using the stock configuration - No Change.
C. Changed out the spark plugs - No change
D. Used a very high end IBM laptop, 3.X gigHz - No change.

Last thing I plan on doing is changing out all the plug wires with that of my fathers off his 555CI motor. I will try that tonight,,,ran out of day yesterday and the 4 yr old was tired - so I had to call it a day.

One last thing I can think of that might be a problem is the db9 cable that comes with the DFI was too short and I am using a standard DB9 that is pretty long to extend it to the laptop. I can try to shorten that.

Also I had the box that is on the logging cable setting on the msd box, but that should have been eliminated as the culpret when I unhooked the MSD.

I have a inverter in the car also....not sure if that matters...but I will pull it out of the car and run a log off just the battery of the laptop tonight.

Anything you guys can think of, would be greatly appreciated. I have eliminated about as much as I can think of and KNOW the car will go faster now that I hear this mild miss.........keep the suggestions coming. I am starting to become stumped.

Hopefully the changing of the wires will solve the problem...

Thanks again...

 

[ski_dwn_it]

OK nother update....

GOt the miss fixed...put my fathers wires from this chevelle on it and now the car is not popping. So I must have had a bad wire. First time I have ever seen a Taylor 10.4mm wire go bad, but guess it can happen anytime, with anything. New ones on order.

Now for the bad news. Upon review of the logs, the RPM flutter is still there. Damn this is starting to get annoying.

Now everything in the entire ignition has either been eliminated or swapped out.

Starting to run out of I-DEE-ERS.....

 

[QuickWrench]

Do your data logging parameters include MPH, wheel speed, converter speed, or driveshaft speed? If your engine's truly fluttering its speed under acceleration, it will show up there, too. That would determine if it's a logging problem, instrumentation issue, or if it's legitimately happening.

You mentioned running an HEI...are you running an on-distributor cap, or a remote one? Did you change coils when you swapped the distributor?

Where are you actually feeding the RPM signal from? The coil? Distributor tach feed? MSD box? Crank trigger?

 

[ski_dwn_it]

Quick..

The distributer is an HEI, stock ingition with an aftermarket coil fixed on top the cap. Lots of spark when you check it, jumps about 2 inches, with a nice strong snap to it. Got nailed a while back by it, and it went in my right hand as I was trying to adjust the timing and it shot off my left hand about 1 inch to the plenum.

The miss is now gone. but the RPM flutter is still there.

Only thing I can think of doing now is wrapping everything in aluminum foil and see if that works. I had a romulator, stock real time device, that I had to do that to to keep down RF signal interference. Sorta looked over my should both ways to see if anyone was looking as I wrapped it up, but it worked and I got no more interference.

I will try that perhaps tonight if time permits and report back.

 

[aDFIguy]

If you haven't got this figured out yet, call the DFI tech line...248 380 2780. Ask for Craig, he's got some ideas.

 

[norbs]

I have great tech support from Accel and Fast on my problems, just accel is just a bit busy sometimes, but they still will call you back.

 

[ski_dwn_it]

I tried to call them today, but only have a few moments throughout the day to call them and spend any appreciable amount of time. Will try again tomorrow.

thanks