MP62 - Not faster than stock!?
Posting for a friend:
Having issues with a newly installed MP62 kit on a 94 miata. Running a Moss Fuel card and a Jackson Boost Timing Controller. All settings to manual recommended modes. Also running dual throttle bodies and an intercooler. No afr guage now, but coming shortly. The car produces the expected 7 psi of boost, but is not any faster than a stock miata in a straight line under WOT. The vacuum is fluctuating strangely. Under cruise, it is normally about -12, but a light application of throttle, and the vacuum drops to -3 approx. When lifting off from acceleration, a pffft air sound can be heard from under the hood. Pulled plugs, and they looked fine. Compression and leak down tests were okay before install. Realize that the first obvious step is to get some a/f readings, but any suggestions of things we should look at to check? Thanks guys! |
The bypass valve unit / bypass arm seems to be a weak link, may be worth checking that that's functioning properly and not cracked/damaged. Sometimes the bypass arm doesn't retract and can get stuck too.
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He has a boost leak
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Is the 7psi boost reading coming from the intake manifold? If it is, I would think that points to something other than the last 2 posts. Let us know what you find.
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If you're seeing 7 psi at the intake manifold, stop driving it. Get a afr gauge.
Im going to assumed you used spade terminals to hook those cards up. Pull each one apart and see if any of the spades are bent and not making contact. |
Originally Posted by pdexta
(Post 1334993)
Is the 7psi boost reading coming from the intake manifold? If it is, I would think that points to something other than the last 2 posts. Let us know what you find.
At what point does it make 7psi of positive pressure? This isn't making sense. |
Originally Posted by guttedmiata
(Post 1335000)
I didn't even notice he said it was making 7psi. Also stated is 12lbs of vacuum at cruise and 3lbs on light throttle.
At what point does it make 7psi of positive pressure? This isn't making sense. I too suspect a bypass valve issue, as they are a known wear item. http://trackdogracing.com/supercharg...uatorunit.aspx |
Mine just failed. The diaphragm ripped. This is typical.
When the diaphragm rips the bypass actuator will not open the bypass butterfly. There is a spring holding the bypass butterfly closed. This means the supercharer is always trying to make boost (even at idle). In other words, if the bypass actuator has failed in the typical fashion, it won't cause low boost. It will cause a no bypass situation. |
As far as I know he makes 7psi on the boost gauge, which is connected to the back of the intake manifold, if he had a boost leak, he wouldn't show positive pressure at the intake.
He is wiring an afr. We checked all connections and fittings/vacuum hoses. All checks out. He will be changing out the bypass valve just to rule it out. Any input? |
Originally Posted by Frenchmanremy
(Post 1335084)
As far as I know he makes 7psi on the boost gauge, which is connected to the back of the intake manifold, if he had a boost leak, he wouldn't show positive pressure at the intake.
He is wiring an afr. We checked all connections and fittings/vacuum hoses. All checks out. He will be changing out the bypass valve just to rule it out. Any input? .02 |
Originally Posted by good2go
(Post 1335087)
If the bypass is failing, but not dead, he can make boost, but probably not hold it reliably. Also, the synchronization of the dual TB's, as well as the off-throttle butterfly position on the SC TB can make a huge difference in "air noises" made both on and off throttle.
.02 |
Originally Posted by Frenchmanremy
(Post 1335095)
It holds 7psi steady, just not going any faster...
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there needs to be somethings looked at if the Intake manifold is seeing boost
maybe it's super lean and knocking restriction in exhaust super rich and (I'd assume you'd notice it miss firing) timing is super low something is not right I don't know how people have the guts to go wot without a wideband you need a wideband before you can judge anything |
Originally Posted by Shortpersonbk
(Post 1335100)
there needs to be somethings looked at if the Intake manifold is seeing boost
maybe it's super lean and knocking restriction in exhaust super rich and (I'd assume you'd notice it miss firing) timing is super low something is not right I don't know how people have the guts to go wot without a wideband you need a wideband before you can judge anything |
Originally Posted by good2go
(Post 1335113)
Besides a bad fuel and timing, the idea of an exhaust restriction (broken cat) is rather intriguing. He'd have limited power, but have no trouble making boost.
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Originally Posted by good2go
(Post 1335087)
If the bypass is failing, but not dead, he can make boost, but probably not hold it reliably. Also, the synchronization of the dual TB's, as well as the off-throttle butterfly position on the SC TB can make a huge difference in "air noises" made both on and off throttle.
.02 if there is boost present in the intake, and you're not making more power than stock, your tune is bunk. Bad cards, or bad connection. |
If it feels/is faster at part throttle than at full throttle, it's running lean.
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Defenitely not the connections, he makes circuits for a living, everything was soldered and tested. Power cards could be bad, or the cat could also be bad, I like that bad cat idea, I'd never thought of that!
Car isn't missing, although I did feel some hesitation going through the revs slowly. Plugs were black with soot, leading me to believe running rich. |
Originally Posted by Frenchmanremy
(Post 1335166)
Plugs were black with soot, leading me to believe running rich. get a wideband |
Originally Posted by nitrodann
(Post 1335169)
yeah it ran rich at one point, but when?
get a wideband |
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