Frenchmanremy

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!

k1l4m

iTrader: (2)

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.

guttedmiata

He has a boost leak

pdexta

iTrader: (17)

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.

williams805

iTrader: (2)

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.

guttedmiata

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.

good2go

iTrader: (2)

The bypass on the compressor will not close unless manifold vacuum gets below a certain point (theoretically zero, but can be more like -1 to -2), so it is totally possible, and normal, to be able to drive and cruise without ever invoking the compressor, provided you don't lead foot it. This is how they were able to pass CARB on these, since the system is never really active under light driving/ smog test conditions.

I too suspect a bypass valve issue, as they are a known wear item. http://trackdogracing.com/supercharg...uatorunit.aspx

williams805

iTrader: (2)

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.

Frenchmanremy

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?

good2go

iTrader: (2)

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

Frenchmanremy

It holds 7psi steady, just not going any faster...

nitrodann

The tune is completely fucked, obviously.

Shortpersonbk

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

good2go

iTrader: (2)

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.

x_25

Our Volvo 240 did that with a cat once. It wore into a perfect sphere and would occasionally plug the exhaust. Would go from making... umm.. well, as much power as a 240 ever made, to making about half the power a Beatle makes, but otherwise run just like normal.

williams805

iTrader: (2)

Nope. The spring probably isn't dead. Which means boost is there. Also, he says 7psi. Tune is bunk. They said they checked, but I don't know what that means. Seen a few look at the spade connections and say "looks good". In reality, there was no connection.

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.

Reverant

iTrader: (10)

If it feels/is faster at part throttle than at full throttle, it's running lean.

Frenchmanremy

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.

nitrodann

yeah it ran rich at one point, but when?

get a wideband

Frenchmanremy

It will be installed this week.