Intermittently runs poor at low TP

[portmod7]

I have an MS-II v3.0, 2.905 code. It is on a Gen-I small block Chevrolet 5.7L. I have also done the MSnS-E Modification.

I've gotten it to where it runs pretty strong when everything is working right. However, I have this intermittent issue where my motor runs poorly, almost sounds and feels like it is missing(but i don't think it actually is), feels like I'm lugging it in too high of a gear, and shakes/vibrates roughly under any kind of load unless I open the throttle to say 75% or more.

It happens at all RPM's really, the only thing that seems to affect it is throttle position. It wants to pick up and run correctly when I open the throttle up. It doesn't matter how fast I manipulate the throttle or what RPM I'm turning, just that when the throttle gets around 75% open or more it runs well and picks up speed nicely.

It happens when the engine has been sitting a day or two and is cold, after its been running a while and is hot, temperature or time since it ran last seems to make no difference. The only thing consistent about it is that if I power up the computer and start the engine and it wants to run correctly, it continues to run correctly until the power is cycled off. If I power it up and its not running correctly, it will do it until I power it off. If its running poorly, I can turn it off and start it again until it runs correctly. It usually only takes a couple power cycles to get it right. I've powered it off and restarted it while the vehicle is coasting and had the problem go away several times now. So that leads me to believe that the only factor effecting it is how the computer "boots up" each time.

Any help or suggestions would be greatly appreciated!

[kjones6039]

As always, a log and msq would be quite helpful.......

Ken

[portmod7]

I was finally able to get a datalog of the problem. It seems to do this every other time I drive the truck. Then, with a couple key cycles, it clears right up. On the datalog, the first segment is when it is running like I describe above. Then you can see I cycle the key off/on (while coasting down the highway) and for the second segment it is running "correctly". I've still got a quite a bit of tuning to get it to run like a production car, but it doesn't run too bad when it's running "right".

Thanks for any help you all can give me.

[Matt Cramer]

Try flattening out the VE in the idle area - there's a couple odd peaks there.

[portmod7]

Thank you for taking a look at my files and the response!

The spikes were made by VE Analyze Live. Shortly after I started using it to try and get my VE dialed in, it produced those spikes. Before that, I could not get the truck rolling from a stop without burning up the clutch. It ran very poorly in that range, it was all I could do to get it rolling without killing it. After VE Analyze Live had been doing its thing for a while and I could leave stoplights no problem I noticed the spikes, so I smoothed them out like you suggested. It went back to stalling every time I tried to pull out of a driveway or leave a stoplight. I went ahead and let VE Analyze Live tune on it, the spikes came back, and I can let the clutch out fairly aggressively with almost no throttle input and it will take off from a dead stop like a dream.

So, if you suspect something else that my VE spikes at idle are masking, I would be glad to fix it and smooth out my VE. But I already know that just smoothing out those spikes will destroy my trucks ability to get rolling from a dead stop.

[kjones6039]

But I already know that just smoothing out those spikes will destroy my trucks ability to get rolling from a dead stop.

Possibly an AE issue?

Ken

[portmod7]

But I already know that just smoothing out those spikes will destroy my trucks ability to get rolling from a dead stop.

Possibly an AE issue?

Ken

I could be wrong, but I really don't think so. It's not that I couldn't get the RPM's up from idle with no load, or that it wouldn't respond to throttle input, or anything like that. I would have to hold the throttle/RPM's higher than idle, while cycling the clutch pedal to get rolling, it just had no power to get the truck moving if I engaged the clutch right away like you are supposed to. Trying to get rolling from a stop in 2nd or 3rd gear is what it was like. At that time I tried "playing" with the AE and never really got anywhere with it. That's when I got frustrated, broke down and bought the full version of TunerStudio. I also went through the "Tuning" section in the MegaManual; it said you shouldn't mess with the AE until you had the VE table dialed in, I was nowhere near that point, so I put the AE settings back to the "default". Just letting VE Analyze Live tune while I drove did wonders for the driveability. I was scared that I went too high with my rear end gears for a while, but like I said, the spikes seem to have taken care of it. I can fully engage the clutch and get rolling with almost no throttle input now, like any factory equipped EFI vehicle I've ever driven. There are some SMALL issues now under acceleration that I think are AE related, and I plan to work on, but they are almost non-existent when the system is working correctly.

I sure wish I could figure out what is causing it to run poorly inconsistently. Like I said, it seems entirely dependent on how the system "boots up", or configures itself at key-on. The IAC valve crossed my mind since I know that it moves and reaches a certain setting based off startup parameters, but I tend to rule that out since it's a speed density system, and the problem doesn't seem dependent on the opening of the throttle blades, just on the feedback from the TP sensor. I have to open the throttle past the point where it stops helping acceleration for a bit with no improvement, where it acts like it can't possibly take more air than the throttle opening is supplying, and then the TP gets to a different point where the rough acceleration cleans up and it starts pulling hard. It also makes no difference how fast I manipulate the throttle, so it doesn't seem like AE to me. I can also hold the throttle constant and it continues to run rough as long as I hold the throttle constant. I really think it's tied to the feedback from the TP sensor somehow.

It really affects the driveability when you are trying to cruise and keep constant speed or slight acceleration for an increase in speed limit. The only time it runs correctly is if you put the pedal on the floor. Cycle the power to the ECU once, or twice, maybe three times and it goes back to cruising like you know it can/should. Cycle the power to the ECU again when you stop at the store and it may or may not run right again when you fire it up to leave.

Thanks guys!

[portmod7]

Hi guys, bringing this one back to the top. I was thinking about updating to the v.2.920 code to see if it changed anything for me. Is there any reason I shouldn't try that?


Thanks!

[kjones6039]

I can't think of any reason to not upgrade...........

Ken

[portmod7]

I can't think of any reason to not upgrade...........

Ken

Thanks!

I guess that's more of what I meant.... I thought if nothing else it would be the latest, greatest code version. The main reason I was considering it was the hope that maybe there is a problem with the code currently on my ECU, maybe it just got messed up when it loaded or something, and reloading it might clear up my problem. I haven't messed with it yet though, I've had the truck tucked away trying to keep it out of bad weather.

I just can't understand why my system seems to be so inconsistent. If it was running the same every time I turned it on, sure, I could work with that. But the fact that it runs differently every time I turn it on boggles my mind, and makes it impossible to try and improve the tune. That's why I wonder if it's something in the code. Maybe there's also a possibility that I have a sensor giving inconsistent readings every time it's powered up?

[Matt Cramer]

Yes - a sensor giving inconsistent readings can cause an issue like that. Try gathering multiple data logs and looking at the sensor readings - particularly barometric correction.

[smokey212]

I have this same issue myself. I haven't spent much time tuning lately though because of work. Somehting else my truck does is I can start it up and drive down to the store stopping at redlights and it idles around 900-1000rpm which is were I set the idle. Then when I stop and cut the engine off and start back up to go home it will sometimes idle all the way downt to 500-600 rpm. It's almost like the tune changes sometimes when you boot up. I'll keep following this thread and if I discover something I'll post back.

[Matt Cramer]

I have this same issue myself. I haven't spent much time tuning lately though because of work. Somehting else my truck does is I can start it up and drive down to the store stopping at redlights and it idles around 900-1000rpm which is were I set the idle. Then when I stop and cut the engine off and start back up to go home it will sometimes idle all the way downt to 500-600 rpm. It's almost like the tune changes sometimes when you boot up. I'll keep following this thread and if I discover something I'll post back.

Can you post your current MSQ and a data log of what's happening with the different idle speeds?

[portmod7]

I have this same issue myself. I haven't spent much time tuning lately though because of work. Somehting else my truck does is I can start it up and drive down to the store stopping at redlights and it idles around 900-1000rpm which is were I set the idle. Then when I stop and cut the engine off and start back up to go home it will sometimes idle all the way downt to 500-600 rpm. It's almost like the tune changes sometimes when you boot up. I'll keep following this thread and if I discover something I'll post back.

I am sorry you are having issues too, but I'm glad to know I'm not the only one. Mine also does what you are describing. And sometimes, at startup, I have to hold the throttle open slightly to get it to fire. Other times, with the same conditions, it will fire right up without manipulating the throttle. I thought maybe I just needed some warmup enrichment or some other similar problem to work on. I have not paid attention to see if these starting and idling issues coincide with the issue I started this thread for.

I still haven't touched mine to try and update the code or anything. Too busy with other things

[smokey212]

I have this same issue myself. I haven't spent much time tuning lately though because of work. Somehting else my truck does is I can start it up and drive down to the store stopping at redlights and it idles around 900-1000rpm which is were I set the idle. Then when I stop and cut the engine off and start back up to go home it will sometimes idle all the way downt to 500-600 rpm. It's almost like the tune changes sometimes when you boot up. I'll keep following this thread and if I discover something I'll post back.

Can you post your current MSQ and a data log of what's happening with the different idle speeds?

Matt,

I will data log the next time it happens. I did some tuning this past week again. I had an issue with my LC1. It stopped working and I had to go throught the setup process again with the whole LED and momentary switch etc...

Not sure why that happened, but the AFR gauge in TS was jumping from 19ish to 7 and back. Once I reset the controller it was happy again. I did get it running better than it has been though.

On issue I am still having is when I use the EGO correction. The truck surges ever so slightly and you can see the oscillations in data log. I will post the tune and data log I have from this weekend and see if you see anything. It runs fine with EGO correction off.

I'll start a new thread so I'm not hijacking Portmod's post.


Portmod,

Keep plugging away at it. I've found most of the issues I've had were self induced. Mostly because I was an old school carb guy(at 32 yrs of age ) and the tuning stuff like this was something I had never done. I have enjoyed this experience for the most part and plan on doing my 500hp mustang engine next. It's in my 65 fastback though so it's going to be a little more exotic setup.

[portmod7]

An update to this....

I am now running 2.920 code, but it made absolutely no difference that I could tell. It's a Gen-I small block Chevrolet 5.7L. I have a GM distributor with the 8-pin module, small cap, and external coil.

I finally had the ambition and time to dig into this yesterday and I think I can say fairly confidently that it is an ignition timing issue. To test it, I disconnected the 5V supply to the B-pin on my distributor. Instead of just setting the trigger offset, I just set the timing at 34* advanced with my timing light and left the B-pin disconnected. I went for a quick drive and the truck ran much better than it ever has, even better than when I thought it fired up and ran "correctly" as I described above. It would do rolling burnouts in 1st gear on dry pavement, it would never think about doing that before. It killed a lot of the idle surge I had been having, the truck has always almost stalled every time I push in the clutch to stop at a light, but not with the timing set at 34*. I also cycled the power to the ECU probably 6-7 times and it never made any difference, the truck ran the same every time.

When I first disconnected the B-pin, I noticed that my trigger offset didn't seem to be set correctly. So, after the above experiment, I attempted to reset the trigger offset and see if maybe that was my issue. While doing this, as well as when I set it the timing to 34* above, I noticed that my timing jumps around a bit. From what I can tell, it fluctuates at least 8*. The fluctuation seems to loosely respond to engine speed, more RPM seems to keep the timing advanced about 8* from where it would be at idle, but it will still bounce to the idle timing number intermittently. Also, I noticed that it might even advance another 5-8* or so at even higher RPMS, but I didn't test that too much because I was worried about being rough on the engine and making the neighbors mad. The fluctuation almost always appears to be the same amount. It's never a couple degrees, then 8 degrees, then 2 degrees, it's ALWAYS about 8 degrees. Back and forth, back and forth, instantly, it's not a smooth fluctuation at all.

What I noticed when setting the trigger offset is that if I got it correct at idle, at high RPM my timing light would show around 10* more advanced than the trigger wizard in TS. If I set the offset at high RPM, my timing light would show around 10* more retarded than the trigger wizzard.

I took the truck for another spin with the B-pin connected to 5V, I never even shut it off after setting the offset, just connected the B-pin, and the truck ran badly like I had experienced before. I cycled the power to the ECU while coasting down the road and it ran better like I had experienced in the past, but nowhere near as good as it did with 34* of timing.

So, I got the truck back home, disconnected the B-pin to attempt to set the timing at 34* again, but I must have failed because of the timing fluctuation I was seeing, the truck ran poorly like it didn't have enough timing. I put the timing light back on, advanced the timing to 34* the best I could tell, and it ran much better. I tried cycling the power to the ECU a few times, it made no difference with the B-pin disconnected.

So, at first I wanted to conclude that the timing control in my MS-II wasn't working correctly for some reason. But, it seemed to work very nicely when setting the trigger offset, so I'm not sure that's the problem. However, the truck running the same after numerous ECU power cycles and the B-pin disconnected leaves me feeling like the problem could be in my ECU. Although, my other thought is that since my timing jumps around so much with the b-pin disconnected, I have a bad ignition module, and that is affecting the ECU's ability to consistently control the timing.

If it is a bad module, then that makes 2 that have gone bad in this system now. The first was in an MSD Street Fire distributor, and now this GM unit. What could cause that? I've read that a bad ground can do it, I've got my coil mounted to the firewall and a ground wire ran to the block.

Any help would be appreciated, thanks!

[portmod7]

Also, I forgot to add, the engine runs better, no matter what timing scenario we are talking about, above 75% throttle like I put in my original post, it's really strange to me. However, with a constant 34* of timing it runs great no matter what the throttle position.

If a moderator wants to move this post into the "Ignition/Timing" section of the board, I would think that's where my post belongs now.

Thanks!

[Matt Cramer]

It sounds like the module is working, but you may have "Ignition Input Capture" set backwards or the VR sensor backwards.

[portmod7]

Thank you Matt, I will give that a try and see if it fixes it.

[portmod7]

I checked tonight, "Ignition Input Capture" was set at "Falling Edge", so I changed it to "Rising Edge" like the Mega Manual suggests. The best I can tell by my timing light, that seems to have retarded the timing from where I set it yesterday, the way the engine runs seems to confirm that.

However, the timing is still jumping around when using my light, about 8 degrees. What can cause this? Bad module? A bad light? I bought the light yesterday, a Craftsman dial-back from Sears. The distributor and ignition module are over a year old, but have very little time on them. I had the b-pin disconnected.

Once I discovered the timing was still jumping around I didn't go any further. I figure I need to solve that issue before I worry about anything else. Any ideas?

Thanks!