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johnhup

MegaSquirted ITB's continued - possible vacuum leaks (long)

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Alright well to follow up on my last post, I have gotten the MAPDaddy properly configured on my MS is reading it right. About 101 at sea level and fog, and when I suck on the hose to complete vacuum I get around 40 kPa. This definitely puts me on the right track.

Now, I rechecked all my hoses and retightened all my intake and throttle body bolts but I still am only getting about 90 kPa at idle (that is right before the motor dies). Now I tried shifting my table to account for it in a crazy fashion, making the kPa start at 90 at the bottom and 100 on top but that didnt help because my reading was somewhat erratic. The motor still seems to surge.

Now I tried setting up Alpha-N but that doesnt seem to work either. Granted I am really new to this but I am pretty sure I grasp the theory. Should I at least get the motor to stay alive?

This is leading me to think I am having other issues but nothing else has changed. Distributor is at the same marks I left it, all plug wire are in place. I am getting sparks obviously which leads me to believe all that is still in order.

Could I be having leaks in between my intake manifold and ITB's? I only have rubber o-rings that sit in a groove between them. They look like they are being over tightened. I am thinking of removing them and adding paper gaskets like on the head.

If I had a good seal shouldnt I get a low MAP reading right around idle? Maybe in the 40 kPa or less range? My cam isnt that aggressive so valve overlap isnt an issue. Even if my injection timing was off, wouldnt I still be seeing low kPa values?

Maybe I am getting bad or erratic values from the tach, but it does seem to match the sounds that I am hearing pretty well. I am almost totally out of ideas. I am about to take it all apart, put it back together, try and if that doesnt work call up JP at A1 imports.

EDIT: Added photos

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Aside from other issues that you will have to discover by carefull checking, I would suggest you take the map hose to a point equally in between 2 and 3. Then connect the tube from 1 to 2 and 4 to 3. You may be reading an average intake pressure from cyl 4.

There is air movement between the TBs within the tube and because of that the actual cylinder pressure in intake will not be represented (Air from the TB next in the firing order is flowing in the tube towards the cylinder that just took a gulp of air and the map will read the pressure of about half way between the two).

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I'd try taking all those T's off and just running it to one runner and see what happens.

I understand that there will not be enough of a plenum to get a proper map reading with ITBs. I know I read a workaround on the megasquirt forums somewhere.

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should be much lower than that at idle. Try squirting some carb cleaner around the gaskets and check for changes in the idle behavior. I think that is the root cause of your problems.

John N

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I think I am going to have to rip everything out and plumb it all up again. A leak would definitely account for my problems. I will also try reading the MAP from in between cylinder 2 and 3.

I keep thinking to myself it has be something else, but if I cant get a good MAP reading then thats really where I should focus my time until I can prove otherwise.

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Jim,

I was just going over some old inspiration pictures and I happened to come across yours. I can see you took the MAP reading in between cylinder 2 and 3 like you suggested. Did you ever have it like my setup reading from close to cylinder 4? This is the most promising thing I have come across so far.

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John,

You said you tried alphaN and had no change. Alpha N should take the whole MAP out of the system. I have been planning to use alphaN for idle and low rpm and transition to MAP when the vac becomes useable. JimK knows a LOT more than me on this but something else might be wrong if alphaN doesn't work too.

John

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High MAP is not unusual if the engine has not really "caught" yet. Have you actually had the engine at or near idle, or above the crank speed? If not you really can't judge how much vac it will draw. These first few seconds of running are frustrating to be sure, and your ITB's make it all the more difficult.

I really would not create a VE table so compressed though, worst-case the idle should be at least below 70. Checking for leaks, is always good, make sure you have not fouled the plugs. The advice on making sure that the vac tubes are equal length is spot-on though.

There is also the off chance that if you flashed some info to the MS while the batt voltage was low (ie after lots of cranking) there might be corruption, either pull the MS and flash the msq while powered by the stim or try flashing it again when the batt has recovered.

I guess I would step back and go through the whole setup methodically (fuel pressure, spark, injectors opening, settings in MT?), something has to be off a bit, short of flooding, fuel with spark should run, maybe not well, but better than your getting now.

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Yea I had it running for almost 15 seconds the other day while it was fluctuating between 700 and 850 RPM's. The vacuum was still reading in the 90's.

The fact that I couldnt get AlphaN to run does still bother me though. That should work even if I do have a small vacuum leak somewhere. I will give it another try after I try to get a solid MAP reading again. I would rather try and run MAP for obvious reasons. I have been planning this for a long time, hence keeping my cam mild.

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John,

In what appears to be your 1st photo, it looks like the manifold (cannon??) doesn't match up well with the TWM throttle bodies.

You shouldn't be able to see the oring. And as long as you have the right diameter/cross section o-ring and TWM didn't mess up the groove, they shouldn't squish out.

From the pictures it would appear there is not enough sealing surface on the manifolds to properly interface with the TWM throttle bodies. This very well could be the cause of your intake leaks.

I'd try a temporary method like using a paper gasket or some sealant to see if it helps. The carb/brake cleaner sprayed at the joints should easily find any intake leaks as has been suggested.

Eventually, I'd recommend getting a better manifold. The o-rings are really robust and seal very well in most applications. We use some here at work that look puny in cross section but withstand 30 psi of boost and extremely high temps in the engine bay.

Goodluck,

Bernard

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If you insist on running a MAP I still think that making an actual vacuum plenum (all equal length tubes from intake runners meet up to some container) and put the sensor in the said container. Im sure the mentioned way of averaging the pressure from runners 2 and 3 as mentioned will work as well (it seemed to for the other guy).

Since your car can't run off just a throttle reading, like the others I think something else is wrong. Hopefully its just a simple leak to fix and then you can get this car running!

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Jim,

I was just going over some old inspiration pictures and I happened to come across yours. I can see you took the MAP reading in between cylinder 2 and 3 like you suggested. Did you ever have it like my setup reading from close to cylinder 4? This is the most promising thing I have come across so far.

You gotta think through what is happening with respect to runner pressure through all four strokes of a cylinder and what the other runners are doing at the same time and you will understand why tapping of no 4 is no good. When cyl 1 finishes intake, cyl 2,3,5 runners are all at higher pressures, so air is traveling in the tube towards no. 1. On the next stroke it all changes and air is traveling in the tube in the reverse direction towards cyl 3, and so on through the 4 cycles.

Your idle pressure when you finish tuning will bounce between 50-60 on the MAP with ITBs because of the characteristics I described. Whereas with a common plenum it might read approx 35 on the MAP. After you study it a while you will understand that the MAP reading with ITBs does NOT represent cylinder pressure on intake.

I've been through what you are now discovering, plus I had to overcome the troubles that great changes in altitude present (no the party line that the ECU mfrs expouse about modern day MAP sensors doesn't apply for ITBs).

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Its actually a Mangoletsi manifold, but the mating does seem funny. I could never see the o-ring before, I can now because I have been tightening the hell out of it.

Once I get this thing to idle I will spray some carb juice at it to see if thats the problem.

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Since your car can't run off just a throttle reading, like the others I think something else is wrong. Hopefully its just a simple leak to fix and then you can get this car running!

I can also say that for running of TPS, tuning for driveability will be tricky, because at cruse at 65mph, his throttle will be less than 5% open with his setup (have the same). I am tuned with MAP and have zero driveablilty problems at low throttle, low speeds, and much better driveability than I ever had with a carb.

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I will get this MAP to work if its the last thing I do. I have a very similar setup to Jim minus the altitude which should make it even easier for me!

I will find any and all leaks and make all my vacuum tubes the same length, taking a reading in between 2 and 3. Who knows. It may be driving tonight!

Thanks to everyone as usual. I will post my findings whether you all like it or not ;) I will also make a YouTube video so you can all see and hear it run (fingers crossed).

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