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Took my car out for a little joyride today and while reviewing some data, noticed some fluctuations in the RPM during the pull.
Look at the RPM line on the graph. I recall my last motor doing this same thing and I attributed it to valvefloat but I can't see that being a problem on this motor within the range I'm turning it.
Is it normal for it to "stray" that much?
Note that I was using the same distributor, coil and module on my last motor in case that may have something to do with the odd reading.
Let me also add that the fluctuating readings are enough to cause undesirable results.
Example. I had my fuel cut limiter set to 6500rpm. I was taching 2nd out barely past 6000 and as I went to do the 2-3 shift the entire engine shut completely down.
Reviewing the data logs showed a couple 6400+ spikes. The "jitter" seems to increase with rpm.
The strange part however is look at the rpm climb in 1st gear. It's dead steady.
Fluctuations would seems to be related to signaling to the ECM from the coil/distributor, especially with 6500 limiter shutdown at a reported 6000. What do you see when holding a steady 3000 RPM for a few seconds.
What's the frequency in that rpm graph? How many samples per second? Have you checked your distributor gear and cam gear? Is there any wear on them?
The entire engine, with the exception of the distributor (Which is a drop-in DUI unit with their module and coil, and all other components replaced), which racked up a few k on the old motor, only has around 1700 miles on it. Distributor gear looked great last time it was out. Due to leaking end rail seals on my manifold , I will be pulling everything back apart soon and will check it at that time.
Originally Posted by 84Elky
Fluctuations would seems to be related to signaling to the ECM from the coil/distributor, especially with 6500 limiter shutdown at a reported 6000. What do you see when holding a steady 3000 RPM for a few seconds.
I will have to try that and see.
Just a few ideas here That I could see as contributors. The wiring in my car feeds the ECM the RPM signal through a single lead coming off the coil (Stock wiring) that passes through the driver side bulkhead connector into the vehicle. Also sharing this same wire are my digital cluster, autometer 5" tach and viper alarm (For the remote start).
I recall the digital cluster for some reason had issues with the tach signal coming off that coil. Above 3000rpm it would bounce around severely to the point that you couldn't tell what it was reading. A 10k resistor inline with the tach signal wire to the cluster seemed to fix this. Note that this resistor was only placed on the cluster. The rest of the devices still have a direct connection to the coil.
Vehicle is also running resistorless spark plugs. I do not seem to have any radio interference issues from them on any devices in the car. I don't even get ANY audible feedback through my speakers or amps.
Just trying to think of things that could be contributing. While the vehicle is accelerating, it does not SOUND like it spiking and dipping like the graph shows, and both my digital and analog tachs do not show this.
Here is the graph that trigger the fuel cutoff. I can see it kicking in during the massive wheelspin I was experiencing, but not at the top of second gear like it did:
Last edited by FireDemonSiC; 08-21-2016 at 04:25 PM.
my racing experience using racepak tells me that this is almost always caused by spark plugs misfiring, or possibly wires. But check for low fuel pressure first at that rpm range.
The thing is, I believe this only an issue isolated to the tach signal/datalog.
The engine does not rev or sound like this while accelerating. A sudden 300-400rpm spike that immediately settled back would be very detectable. Especially towards to the top of peak hp where revving outside of the powerband like that would really make you feel it coming in and out.
The thing is, I believe this only an issue isolated to the tach signal/datalog.
The engine does not rev or sound like this while accelerating. A sudden 300-400rpm spike that immediately settled back would be very detectable. Especially towards to the top of peak hp where revving outside of the powerband like that would really make you feel it coming in and out.
The old saying goes, Data does not lie. You have the racepak in the car for a reason, to detect things going wrong that you can't detect by feel. Like I said, most of the time when you see this it is the plugs..
The old saying goes, Data does not lie. You have the racepak in the car for a reason, to detect things going wrong that you can't detect by feel. Like I said, most of the time when you see this it is the plugs..
> Vehicle is also running resistorless spark plugs
Please change this first. With EFI systems you must run resistor plugs and suppression plug wires. The best wires to run will be spiral core.
{edit: adding} while tuning the best plugs are to use the inexpensive cooper core plugs at a $1.89 each.
RBob.
Here is a much older datalog of when I was running resistor plugs. Was able to find a 100% TPS moment through 1st and 2nd. It still look jittery, but I will comment that it appears much smoother in the higher rpms.
Any thoughts? I might try a resistor inline with the tach signal wire first. MUCH easier than changing plugs.
Last edited by FireDemonSiC; 08-21-2016 at 11:18 PM.
The wiring in my car feeds the ECM the RPM signal through a single lead coming off the coil (Stock wiring) that passes through the driver side bulkhead connector into the vehicle. Also sharing this same wire are my digital cluster, autometer 5" tach and viper alarm (For the remote start).
I take it you are not using a computer controlled distributor? The ECM distributor reference has two inputs, one that is a 5 volt pulse (square wave), and the other is a ground reference at the distributor. If there isn't any device to shape and filter the waveform from the coil and it is being fed directly to the ECM, that is not correct.
I take it you are not using a computer controlled distributor? The ECM distributor reference has two inputs, one that is a 5 volt pulse (square wave), and the other is a ground reference at the distributor. If there isn't any device to shape and filter the waveform from the coil and it is being fed directly to the ECM, that is not correct.
RBob.
Incorrect. 7 pin module ECM controlled HEI.
The wiring in the car to and from the distributor is in the same configuration it would have left the factory with.
Is there supposed to be any magic between the tach terminal on the HEI and the ECM?
Also just a thought. But I've been thinking of feeding the coil positive directly off the battery with a switched relay instead of using the harness wiring.
Last edited by FireDemonSiC; 08-22-2016 at 09:36 AM.
The wiring in the car to and from the distributor is in the same configuration it would have left the factory with.
OK, that is correct and works.
Is there supposed to be any magic between the tach terminal on the HEI and the ECM?
None, there should be no connection between the coil and the ECM. If you have added a wire from the coil to the ECM, remove it. I've attached the ICM to ECM wiring diagram for a large cap distributor. At the ICM pin B is the reference pulses to the ECM. With pin D providing a ground reference for the pulses within the ECM.
None, there should be no connection between the coil and the ECM. If you have added a wire from the coil to the ECM, remove it. I've attached the ICM to ECM wiring diagram for a large cap distributor. At the ICM pin B is the reference pulses to the ECM. With pin D providing a ground reference for the pulses within the ECM.
RBob.
Understood that the ECM gets the RPM signal directly from the module and not from the tach signal wire. No extra wire was ran to the ECM in the fashion you are suggesting. No worries there.
Do you have any other thoughts besides possibly the resistorless plugs? I am thinking, based on looking at past logs, that the difference from switching to resistor plugs might be trivial.
Do you think it could be some sort of issue with the module itself? Note that when I first installed this distributor a few years ago, the first distributor failed after 50 miles. I suspected, based on the symptoms, that the ICM had gone south for the winter.
Had the car towed home Called summit, who swapped out the entire distributor.
A little over a year later, SAME THING. Car died going down the road. Had to call for a tow again. Contacted DUI, who surprisingly agreed to a no charge swapout of both the coil and module even though it was out of warranty (After explaining the whole story to them).
I haven't had any issues with it so far (It's been roughly two years, with 9 months of that time my car being laid up inoperable while I was piecing together the new motor).
Lately, even though I have a more than capable HEI setup, I've been debating whether or not to go with a capacitive discharge ignition such as the Pertronix Second Strike. In the very least, I imagine the multiple spark feature could greatly help with cylinder efficiency with the cam I'm running.
Last edited by FireDemonSiC; 08-22-2016 at 11:37 PM.
If you can get your hands on an all GM distributor it would be worth a try. As for adding a second strike box, I wouldn't add anything else until the DRPs to the ECM are stable.
What type of triggering device does the DUI distributor use? A picture would be helpful.
If you can get your hands on an all GM distributor it would be worth a try. As for adding a second strike box, I wouldn't add anything else until the DRPs to the ECM are stable.
What type of triggering device does the DUI distributor use? A picture would be helpful.
RBob.
It looks just like a regular HEI inside. I know I have some pictures of it somewhere. It uses the traditional pickup coil and stator as a triggering device. It's just a normal large cap HEI with their module and coil.
I also remember the radio suppression capacitor being small, red and square. About the size of a quarter.
Reviving this post because the RPM signal is still wonky. Take a look at the attached photo. This is a dyno pull in third gear WITH RESISTOR PLUGS.
The car did put 314/363 to the wheel but look at the RPM graph up until the point the throttle is lifted. Furthermore, compare this pull in third gear with my previous photos that were in 1st/2nd gear. It doesn't seem like changing to resistor plugs had ANY effect.
It seems that the more "time" the engine spends in the powerband, the more erratic the signal gets. Pay particular attention to the time the vehicle spent in 1st gear from my graphs months ago and then compare to the third gear dyno pull for the perfect example of what I'm referring to. I'm stumped. What gives?
RBob? Anybody?
Last edited by FireDemonSiC; 11-29-2017 at 06:05 PM.
Is the switch to resistor plugs the only change made to try to solve this?
Why is the WB O2 signal noisy, just like the RPM value? Although the noise has been greatly reduced with the resistor plugs (previous graphs versus this last one).
It does appear that the RPM fluctuation is more consistent with the resistor plugs. Not as erratic, so they appear to have had some affect.
The ECM calculates the RPM by measuring the time between distributor reference pulses (DRPs). So any inconsistency in the DRPs from the distributor and the ECMs calculated RPM will fluctuate.
What does the RPM look like on steady state cruise?
My ICM ground wire came loose inside my distributor. Caused me to have rpm fluctuations and the car would cut out above 6k rpm. Might wanna check to be sure.
The issue isn't anything such as a loose wire. The car physically runs flawless. This is just what the ECM sees because something is interfering with the DRP signal.
RBob, let me see about getting you a cruise graph. I am not sute about the O2 signal either, although I would go out on a limb and say that it could possibly be the actual fueling going jittery like that due to the RPM signal being scrambled and constantly bouncing the EBL back and forth between cells in the fuel map. It can fluctuate by as much as 3-400RPM within a split second.
Reviewing the dyno logs I noticed the timing bouncing around in this manner around peak torque where I have a dip programmed into the curve from 36 down to 33*, then back up to 36 by 5000rpm. This was with knock retard COMPLETELY DISABLED at the time so the only logical explanation is the RPM signal.
Last edited by FireDemonSiC; 12-01-2017 at 09:47 AM.
As you requested, here is a photo of the signal with the car just cruising down the road. This was city driving and not highway which is why you see the TPS bottom out and the RPM jump (Downshift) at the end. Also note I on a 4 speed auto but with a manual valvebody. Don't wan't any confusion as to transmission type in case that has any bearing.
Do you see any clues?
Also please note, I am getting ready to go back to resistorless plugs as I am preparing to spray the car and cannot find a suitable plug in a resistor style (heat range 7, 5/8 hex, NON-Projected). What made you state that you believed the switch to resistor plugs made an improvement? Signal still looks fornicated to me. Are you saying that while still erratic, the signal at least appears uniform? As in it's not smooth one second and then erratic the next?
Also note, the ignition is a turn-key Davis Unified distributor. Coil in cap style HEI. Also with their "LiveWires" spark plug wires.
Also, I DO have highway mode enabled and the MPH threshold is 45MPH, in case you were wondering about the 15.8:1 AFR. Totally normal.
I'm guessing the ICM could be the culprit, although I'm not as well versed as you are on the subject. It wouldn't be beneath me to try a different ICM. What would you recommend?
Last edited by FireDemonSiC; 12-03-2017 at 09:20 PM.
As you requested, here is a photo of the signal with the car just cruising down the road. This was city driving and not highway which is why you see the TPS bottom out and the RPM jump (Downshift) at the end. Also note I on a 4 speed auto but with a manual valvebody. Don't wan't any confusion as to transmission type in case that has any bearing.
Do you see any clues?
Not really, still a little noisy, but not as bad as WOT.
Also please note, I am getting ready to go back to resistorless plugs as I am preparing to spray the car and cannot find a suitable plug in a resistor style (heat range 7, 5/8 hex, NON-Projected). What made you state that you believed the switch to resistor plugs made an improvement? Signal still looks fornicated to me. Are you saying that while still erratic, the signal at least appears uniform? As in it's not smooth one second and then erratic the next?
Here is a resistor plug, non-projected tip, 3/4" reach, 14mm, 5/8" hex:
NGK BCR8ES (stock number 5430)
The signal is more uniform, not as random or jagged.
Also note, the ignition is a turn-key Davis Unified distributor. Coil in cap style HEI. Also with their "LiveWires" spark plug wires.
I'm guessing the ICM could be the culprit, although I'm not as well versed as you are on the subject. It wouldn't be beneath me to try a different ICM. What would you recommend?
For an ICM, AC Delco.
You can also send the ECM in to us for a checkout. I don't think that this is an ECM issue but we can rule it out.
Not really, still a little noisy, but not as bad as WOT.
Here is a resistor plug, non-projected tip, 3/4" reach, 14mm, 5/8" hex:
NGK BCR8ES (stock number 5430)
The signal is more uniform, not as random or jagged.
For an ICM, AC Delco.
You can also send the ECM in to us for a checkout. I don't think that this is an ECM issue but we can rule it out.
RBob.
RBob, great find on those plugs. However, I am concerned that 8s could be way too cold for my usage. I am pushing give or take about 400 at the crank with a 100 shot that is barely ever used (I actually have yet to spray the new motor after 4k miles of use because I don't believe the trans will hold in its current iteration).
The car is regularly street driven and even known for making short 3 mile trips to and from work with the oil temperature barely cresting 140 on the morning drive. I am concerned that 8s would lead to fouling issues. I generally try to stick with the HOTTEST plug that does not give detonation for a clean running engine.
Also as for the ICM, certainly ACDelco is a no brainer but what are your thoughts on things such as output and dwell time with stock vs aftermarket modules? It's a widely accepted fact that aftermarket coils never see their full rated output unless running an ICM or ignition box that can keep up.
I also do not at all believe it is an ECM issue and will reserve that for a last ditch effort.
Also as for the ICM, certainly ACDelco is a no brainer but what are your thoughts on things such as output and dwell time with stock vs aftermarket modules? It's a widely accepted fact that aftermarket coils never see their full rated output unless running an ICM or ignition box that can keep up.
Dwell is ECM controlled, no difference. Coil saturation can vary as I have found one particular aftermarket ICM current limits at a much lower level then AC Delco ICMs.
As for coil charge time, it has very little to do with the coil resistance. It is the coils inductance that 99% affects the charge time.
Im having worst issues and would like to know where should I start looking.
My RPM signal jumps abruptly but only between 950 rpm and 1200, after that it clears out. Please dont pay attention to the lean mixture , I just changed the cam and I was plotting a open loop warm up test and start adjusting, but it makes very difficult to calibrate that rpm range.
Could this be Ignition Module?
I can't help but notice that the peaks and valleys of the WB O2 fluctuations seem to roughly correlate to the rpm fluctuations.
can you give some more info on your setup? What have you done to the tune so far?
I just wrote the longest reply and lost it all because of the loging timeout!!!! so here is the short version hahahahhaha.
WB02 is reacting to the bad RPM reading, this is in Open Loop so computer is picking up wrong pulse size.
The setup is a L03 from a caprice, EBL, TrickFlow Super23 heads, headman headers full lenght, no cat, 2.25 exhaust, Comp Cams CS 268XFI HR-13, Stock TBI but with new injectors, TPS and IAC. All of this loaded on a IH Scout II with a 4 speed manual transmission .
Im tunning with the EBL VE learn tool in open loop with the What's Up. I was first trying to get a better VE table and then was thinking on explore timing table.
Im not sure where the RPM glitch started, I was doing a different way of tuning in the past (datalogs, export to xls, pivot and mean values of wb o2 vs rmp and vac.) Since I was working with mean values I am not very aware since when this issue is happening.
On the cam replacement I had to replace the ignition module with a generic but compatible unit (there was nothing else available!), why it went bad, I have no idea, it just happened.
So Im not sure if it is the cheap IM or spark plug cables, or a bad connection. But it is very interesting that it is only on low rpm and worst between 900 and 1200..
08-17-2016, 02:29 PM
