545" High Riser Build

[machoneman]

Had the same idea. The engine not pulling crankcase vacuum and it's inability to idle below 1,300 rpm seems consistent with a fairly large yet undetected vacuum leak.  JMO.

[jayb]

I could see potentially a vacuum leak in the crankcase that I haven't found, but that wouldn't affect the idle.  If there was a vacuum leak in the induction system the engine would still idle when the throttle plates are closed.  It won't; as you back off the idle adjustment screw and close the plates, the engine shuts off.   This is also with the plates still partially open; they are not completely shut.  If I shut the plates all the way and the engine still idled at 1400 RPM, I think a vacuum leak would be the culprit; unfortunately that's not what is happening.

[My427stang]

Jay, three things, two air, one fuel

1 - What is your TPS value at idle, and what is it showing when you try to idle it lower?  Wondering if for some reason the ECM thinks that its completely closed and shutting off the fuel

2 - Have you considered trying to close one TB completely at idle and idle off the other?  If your dual TBs are so large that the 1500 rpm idle has them almost closed, by lowering idle even more, you could be closing them completely and shutting the air off.  By closing everything but a single pair of "primaries" they will be farther open and allow some airflow

3 - Could you put some sort of IAC on the manifold?  Then you could close the blades and make it back up with an IAC that adjusts as required.

Finally, how about some sort of log at idle?  Start at 1800......log INJ PW, O2 sensor output, TPS voltage, RPM, fuel pressure if you can, and then log for a 30 seconds or so at 1800, 1500, 1400, 1300, etc until it dies.  There would have to be information that will steer you in the log.

[machoneman]

You're absolutely right Jay. The two events are independent; my bad for a poorly-worded reply. Still,
427 may be onto something. Hope you figure it out and quick! 

[jayb]

Jay, three things, two air, one fuel

1 - What is your TPS value at idle, and what is it showing when you try to idle it lower?  Wondering if for some reason the ECM thinks that its completely closed and shutting off the fuel

2 - Have you considered trying to close one TB completely at idle and idle off the other?  If your dual TBs are so large that the 1500 rpm idle has them almost closed, by lowering idle even more, you could be closing them completely and shutting the air off.  By closing everything but a single pair of "primaries" they will be farther open and allow some airflow

3 - Could you put some sort of IAC on the manifold?  Then you could close the blades and make it back up with an IAC that adjusts as required.

Finally, how about some sort of log at idle?  Start at 1800......log INJ PW, O2 sensor output, TPS voltage, RPM, fuel pressure if you can, and then log for a 30 seconds or so at 1800, 1500, 1400, 1300, etc until it dies.  There would have to be information that will steer you in the log.

Those are good suggestions, Ross.  On the datalogging thing I've been having trouble with the log viewing software that is used with the MS3X, and that has hampered my efforts to debug this problem.  Once I get that working the solution may come.  Also I will check the TPS reading; I did re-calibrate the TPS yesterday when I did the testing, but maybe it was not done correctly or something.  I'll find out more when I get the engine up and running in the car...

[Chad D]

Is there a way to dump log output to a .csv or other flat file format?  Microsoft Excel, or Open Office Calc can read quite a few formats, and perform nice graphing functions.

[My427stang]

Those are good suggestions, Ross.  On the datalogging thing I've been having trouble with the log viewing software that is used with the MS3X, and that has hampered my efforts to debug this problem.  Once I get that working the solution may come.  Also I will check the TPS reading; I did re-calibrate the TPS yesterday when I did the testing, but maybe it was not done correctly or something.  I'll find out more when I get the engine up and running in the car...

If you want to send me a log for an experiment my program says it can read *.csv, *.dbf, *.DB, and *f1p

Of course I am not sure what I will see when I open the file, I'd be happy to give it a shot

[Kirk Morgan]

I would put a good meter on your O2 sensor and look at the voltage. If you have a vacume leak they are going to show lean. I have used to use Propane to try to find vacume leaks also. You also can enrich your fuel mixture to see how the O2 sensor reacts to see if it is working properly.

[cdmbill2]

Jay, I had to fiddle extensively with the throttle blades, both primary and secondary on both TB's to get the closed throttle idle in a range that we tune with the fuel table. I'd like to run the IAC's as Doc McIntyre does, but we got it working without it(them). MY TB's are 2200 CFM dominator pattern units from Accufab with four 2.25" round blades each.

My secondaries are progressive, but the link between the primary side throttle arms is a very precise 1:1 so I did the final fine adjustments on the secondary throttle blades, a few dgegrees of turn makes a huge difference.

With those adjustments we can get it to idle below 1000, but I prefer to keep it at around 1200 to kepp the roller lifters happy and well oiled. With the 5700 stall converter I don't find the street manners to be an issue and I thinks its helped by the AOD that is set up for full automatic function when the full pressure/OD lock out solenoid isn't enaged. The car just oozes along on the street at low throttle openings.

On the vacuum side I'm a bit mystified and would suggest a call to Peterson. That said the benefits between 8 inches of vaccum and 12-15 are small even with narrow low, tension ring packages designed for vacuum pump use. I limit mine to 12" to avoid drying out the wrist pins as I don't have pin oilers.

How are you measuing crank case vacuum? I had been using a basic mechanical Autometer Boost/Vaccuum gauge. With the MS3X I added a standard GM 1 BAR (~15") sensor. The datalogs to date show a rising(?) crank case KPa as I haven't got it calibrated yet based on actual voltage output to read as plus or minus inches of Hg.

[dieselgeek]

A heads up on the TPS function in the MS3X, it's only used for accel pump shot.  It doesn't control the fuel in the defaul tune that I set up.


IMO, the problem is most likely going to be air distribution at idle.  With 8 O2s or EGTs you'd likely see as you get lower in RPM, the EGT/O2s will vary wildly cylinder to cylinder.  The "shut off" point is the point where more cylinders are misfiring, than those firing.


I think working with the plates as CDMBill suggests is likely the best approach.   I'm not sure why you're having an issue with the datalogging, it's very rare, but we can always get on the ms-extra web forums and ask about the problem you are seeing...  meanwhile, keep an eye on the Ignition Advance gauge and the Pulsewidth gauge.  If either of them do something strange when the engine shuts down, then there would be a problem with the tune.  There might be a better combination of fuel and ignition timing than what's in there now, to run below 1400rpm, so it might be that as well.

Meanwhile, once the engine is in the car, the idle tuning will be largely different than that on the dyno, as the dyno loads the engine at low RPMs somewhere around 20-50hp, versus in the car with no load other than the accessory drive.  You might have a much easier time tuning idle in the car then on the dyno.

[cdmbill2]

Had the same idea. The engine not pulling crankcase vacuum and it's inability to idle below 1,300 rpm seems consistent with a fairly large yet undetected vacuum leak.  JMO.

This is interesting and I hadn't thought it through, but a leak from the crank case into the intake tract would potentially explain both sets of behaviors. How that is possible given the valley pan etc. is a different question but it gives you some routes to testing should it be worth the time.

[Chad D]

Had the same idea. The engine not pulling crankcase vacuum and it's inability to idle below 1,300 rpm seems consistent with a fairly large yet undetected vacuum leak.  JMO.

This is interesting and I hadn't thought it through, but a leak from the crank case into the intake tract would potentially explain both sets of behaviors. How that is possible given the valley pan etc. is a different question but it gives you some routes to testing should it be worth the time.

Disable the evac system.  If the leak is in the crankcase, the idle should go further north, as the ΔP increases between the crankcase and the intake ports and unmetered air flow increases with it.

[KMcCullah]

IMO, an outside source of vacuum should be plumbed to the crankcase for troubleshooting purposes. Like that vacuum pumps the HVAC guys use to evacuate a refrigerated system. Draw a vacuum on the crankcase and bump the motor around a few turns maybe...... Check your relief valve settings too......

[jayb]

Had the same idea. The engine not pulling crankcase vacuum and it's inability to idle below 1,300 rpm seems consistent with a fairly large yet undetected vacuum leak.  JMO.

This is interesting and I hadn't thought it through, but a leak from the crank case into the intake tract would potentially explain both sets of behaviors. How that is possible given the valley pan etc. is a different question but it gives you some routes to testing should it be worth the time.

The only possible route between the crankcase and the intake tract is where the port plates I built bolt onto the heads.  I've already checked that; while the engine was on the dyno I pressurized the crankcase with the intake off and looked for leaks in that area, as well as everywhere else that I could see.  For the crankcase leak (if it is a leak, and not a problem with the Peterson pump), it must be in an area where I can't see very well, like the seal behind the cam gear or the rear main seal or something.  As far as a vacuum leak goes, I just can't see how that could be a problem, since the engine shuts off with the throttle blades still open somewhat.  But I'll check more thoroughly for vacuum leaks when I get the engine running in the car this weekend.

[Chad D]

Do you have an oscilloscope view of the waveform for the crank trigger?  A couple of the setups I've worked on were extremely sensitive to air gap between the sensor and the wheel, and behaved spuriously until it was just right.  If you've got a scope and can see the output, it might be worth looking at.