Need help with Megasquirt PNP2 in my 1995 Mustang GT. My car is in the process of being tuned but, has one problem we can't get passed. The car will not rev past 4600rpm. My tuner says that the car runs & drives fine otherwise----it just won't pull past 4600rpm on the dyno... He says it's like it's hitting a rev limiter. Everything he can find is turned off that would be like a rev limiter:

1. Overboost is off
2. Rev limiter is off
3. MSD 6AL has a 6,000 rpm pill

Tuner has datalogged and noticed that at 4,600 rpm in the Megalog Viewer that one setting "rpmdot" jumps from -400 to +1150 very suddenly and the tach in the car actually starts going backwards. He's not sure what this means. Any ideas what this is doing?

I'm actually going to have him disconnect the MSPNP2 and plug the factory computer (with previously burned chip) to see if the car will go beyond 4,600rpm. this should tell us if it's the Megasquirt or not.

Anybody have any input or suggestions? Tuner hasn't given up yet but, doesn't know if there's something simple he's missing in the Megasquirt. Does anyone at "Diyautotune" ever take/work directly over the phone with a tuner if they get stumped?

Todd

 

Have you eliminated the potential for valve springs? What is your plug gap? The FIRST thing I would be inclined to do is tighten it up and see if your issue acts any better. If you're above .025 throw it down that far and see what it does. I'd also be wanting to check timing at the balancer when I threw it on the rollers at speed to ensure that the timing in the ECU is the same as the timing in the Megasquirt. Did you have the MSD box in before the Megasquirt, or did you put em both in at the same time? If the later I'd be wanting to try it with the previous ignition system. Lastly, any plug cuts? What are they saying?

 

Could you email me a data log of the problem and a copy of the tune file to

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, with a link to this thread? I'd like to have a closer look, and these files are generally the first step in assessing what's wrong.

Also, please try setting timing to a fixed angle, and check the timing with a timing light across the RPM range. Timing adjustments are the most common ECU-related cause I've seen of this issue. As Drac0nic noted, this could be something mechanical.

 

Shouldn't be spring related as this has all aftermarket components. I believe a twin spring setup on each valve--no idea on specs as these were spec'd out through an engine builder & tuner. Gaps on spark plugs look good. MSD 6AL was in before adding the MSPNP2. Timing sounds to be good also.

Tuner really thinks something in the Megasquirt ignition settings is not right and is curious as to who can verify these. I'm just a middle man at this point as the car is 200miles from me.

 

Just thought I would drop in here, sorry for this being my first post but seemed pertinent - I fought the same problem for quite a while. Ended up being some sort of latency from the stock TFI unit to megasquirt/megasquirt to TFI to coil, that the latency adjustment could not compensate for. Ended up getting a transistor from Mr. Cramer, using the TFI distributor for tach signal and firing the coil directly, in your case the MSD box. Completely eliminated this issue for me and also opened up a world of tuning "crispness" (for lack of a better term) that really made a huge difference. This is the url for the "mod kit" I used - http://www.diyautotune.com/catalog/bosch-bip373-coil-driver-mod-kit-p-230.html
The easiest way to determine if this is the problem, based on my experience and from Mr. Cramer's advice; is to fix timing at say 15 degrees, rev the engine while watching the actual spark output via a timing light. If the timing retards, you know that there is most certainly a latency issue.

hope this helps.

 

Easy way to fix the ignition settings is to compare them to the base tune, available here:

http://www.megasquirtpnp.com/downloads/maps/index.htm

Note that you will still need to get Trigger Angle and the latency numbers dialed in with a timing light.

 

Found (1) diff in ignition settings. I had the "dwell type" to standard and not "fixed duty". I don't know if the tuner has tried this yet. Matt, if you mean "ignition offset angle" under the trigger wizard then---yes that was done. I'll mention the fixed timing and revving the motor to see if there's any change to him.

 

what tfi module do you have? the fox bodies used the grey bodied one which is fixed duty cycle, most sn95 cars hve the black one which you actually dwell. if you have the blackone try dwell settings from 2-3 ms and spark duration from .5-.7

 

This. I have run into this before as well.
I have also had an issue with tfi moduals that would run the factory ecu, but the MS ecu would have issues. Never the other way around though. Sometimes these issues are a real pain to sort out, but keep at it, my opinion MS is the most user friendly and functional setup there is.

 

Not sure what color the TFI is.... I would assume black since this is a 1995. Tuner switched the "dwell type" to fixed and apparently this is working. Note, "fixed" is what the base tune had in it for a "dwell type" setting.

 

I'll have to check on color. I know now that the Megasquirt "dwell type" to "fixed duty" because the car runs good according to my tuner.

 

Just wanted to follow up on this - does setting the dwell back to "fixed duty" still have it revving out cleanly?

 

Matt, yes the car revs with the dwell set to "fixed duty". Now, I just need to find a tuner that really knows how to tune & willing to tune using the megasquirt. Not many tuners around MN willing to tune the megasquirt unfortunately....