rmoleman

I installed a Lindsey MBC and all new Vac lines. I got it all back together but I have two problems I am not sure how to deal with.


Problem #1
When started (hot or cold) it idles really rough and drives terrible, stumbling and a few backfires, until it is driven for 2-5 minutes then it runs normally. What is the cause?

Problem #2
I set the MBC by driving in 3rd gear and accelerating to redline then adjusting the MBC a little at time until Lindsey boost gage held steady at ~15 psi. The problem is I still get different boost in different gears at different RPM. IN 4 and 5 if i start at low speed and go to WOT the pressure builds and the over boost control kicks in cutting the ignition.
I thought the MBC would give me the same boost in all gears as long as the RPM were high enough. What am I missing?

rmoleman

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Darwantae951

What different boost levels are you seeing in what gears? Explain the problem a little more and then someone will be able to answer. Are you still using the stock wastegate and chips?

-Darwin

rmoleman

Stock waste gate & chips

I set the MBC by making a few runs in 3rd gear starting at ~3k RPM and then going WOT to redline. I adjusted the MBC so that the max boost was ~15 psi. After I set the MBC I did aditional runs in all gears with these results.

1st WOT barely gets above 10 psi, holds there until redline)
2nd WOT builds to ~13 psi then drops to 10
3rd WOT Builds to ~14 psi then drops to ~11
4th and 5th WOT (starting at 3k-4k) Builds to over 15 then over-boost kicks in and cuts the ignition

It seems that the stock trubo can not keep up the pressure at RPM over 4k but can make more then enough pressure at 3k-4k. If you set the MBC so it does not over boost in 4th and 5th then it really dogs in 1st-3rd. What am I doing wrong?

hosrom_951

Set boost to 12psi, 11psi if you can with stock turbo/chips.

Check the vacuum lines again, you may have disconnected one(or more) by mistake.

PS: You set the boost in 4th gear!

rmoleman

Dumb question, but can the waste gate leak if it is not getting any boost signal at all?

hosrom_951

Dont believe so.............

No boost signal, means will stay closed, meaning full exhaust to turbo, meaning max boost.......

Darwantae951

Isn't it a bad idea to use an MBC with the stock wastegate? Single port wastegates will cause irregular boost control (I thought)

-Darwin

bigred1001

I run the lindsey mbc w/ stock wastegate and experience pretty stable boost throughout.

rmoleman

Do you have a aftermarket boost gage? The high RPM roll off is barely visible on the OEM gage but looks huge on the Lindsey Auto Meter gage.

sawood12

I would think it can. The exhaust pressure can push the wastegate valve open against the spring if the spring is weak. In theory it shouldn't as the spring should hold the valve shut, but the springs weaken over time and exhaust pressure can crack the valve open. The wastegate valve is arranged so the exhaust pressure is trying to open the valve and not close it.

Also I think that even with a fresh stock wastegate the valve would be cracking open as a spring is not an on/off device. There is a proportional deflection with force therefore with a single port wastegate the valve will open early. With a DPW there is a second pressure signal (regulated by your MBC or EBC) that keeps the valve fully closed until your pre-set pressure.

I cannot imagine that is is possible at all to install an MBC successfully with the stock wastegate (cue for someone to jump in with storied of their successful installation!!!).

rmoleman

I fixed problem #1 (rough idle). There was one vac line (a very short orange one) back by the firewall that I did not originally replace.

Problem #2 is still there and I have tunned the MBC so that the max boos achieved in 3rd is 14 psi. It drops to ~11 psi at red line. It is possible to over boost in 4th and 5th but you need to be going slow (40 mph) and be at WOT for over 10 seconds before the boost goes that high. As this a very unusual driving condition I am not worried about it.

Do not waste your money on a MBC like me. If you are thinking of putting on a MBC then you want more boost in every gear and the only way I can see to do that with the stock turbo is with electronic boost control because the boost must be at 18-20 psi at 4500 rpm so that it can bleed off boost and be at 14-15 psi at redline.

hosrom_951

With the factory/single port wastegate,one would constantly require to adjust the boost (minor) due to weather conditions (including humidity, not just heat/cold).

sawood12

I'm running an MBC with a DPW and stock turbo and get very consistant boost in all gears. Yes it bleeds off to the top end of the rev range but that is more to do with turbo capacity rather than MBC. EBC's are much much better though. On my mod list!

sin01bst

my lindsey unit does the same thing as far as irregular/varying boost. it also feels like when you lock the button down, it is real loose feeling. i will say that i mounted the mbc in the engine bay(i am relocating/replaceing it now) when i first got it set about a month ago it would hit 15lbs and stay till redline(i have a cat delete pipe, stock exhaust, shimmed wastegate, and an older weltmeister chip). i also only drive this car on the weekends when it is nice out. for maybe the first 200 miles that i drove the car the boost was consistent and strong to 15lbs now lately the boost will vary depending on outside temp and gearing. i really think it is a combination of maybe a small vacum leak and the possibility that the engine heat cooked the mbc??????????i know i shouldnt have mounted the mbc in the engine bay but i was frustrated and had cut knucles from trying to fish the vacume line behind the battery tray. i was unsuccessfull at getting it routed into the cabin. so i took the easy route and mounted it a little bit south of the passenger side strut housing. oh yeah my vacume is between 15inHG and 17inhg when the car is fully warmed up....hope this helps your problem and maybe someone here can give me some insight into my problem. sorry im not trying to thread jack but i thought this might help you also
jason