over boost question.
 

So i do not really know what section to put this in so il just go with general chat..

So i have had a FM voodoo 2 kit on my 91 for about 7 months with a voodoo box and msd box. I finally got away from all that and picked up a msextra. so the problem i am having is i am over boosting. On the previous set up witch was 1.8 injectors with AFM MSD box and voodoo fuel piggy back i was showing 10PSI on my gauge WOT. After installing my megasquirt and removing my AFM and installing an IAT since i removed the AFM i removed the recirculating portion of the valve and have it venting to atmosphere i set my over boost control for 178.5 KPA roughly 11.5 psi and it is fuel cutting and gauge is showing up to 12psi .

My question is what could have changed for this to happen? Any advice for where to look?

What are you using for boost control? Manual controller?

Read this to understand how pressure ratios work: Pressure Ratio | Turbobygarrett

TL;DR: You are making more boost because you reduced the plumbing losses in from of the turbo inlet. Adjust you boost controller to compensate. :bigtu:

Edit: except the MAF really isn't that much of a restriction, is it? Tell us about how your wastegate, BOV, boost controller, MAP sensor and gauge are plumbed. Be specific, draw us pretty MSPaint pictures if that's easier.

no controller just wastegate.. waiting to have a buddy solder in the ebc to my megasquirt

also its a 8psi waste gate.. that comes with the voodoo 2 kit if i remember correctly

is the megasquirt tuned?
if you're running an insanely rich map with retarded timing or something weird like that you can probably generate a lot more exhaust gasses and overwhelm the internal gate

I have my afr table set to where I want and have been letting autotune do it's thing it dosent run crazy rich when this is happening... And the timing is just the base map timing haven't messed with that yet

did you make any changes to your exhaust?

No still running the fm downpipe with test pipe and corksport cat back

If you open overboost protection and change it from 178kpa to 300kpa that should fix the problem. :giggle:

Check the signal to your wastegate, make sure it's reading the same pressure the manifold is getting (attached to wastegate, no holes, no kinks). Make sure the wastegate actuator is adjusted properly as well, if it's too tight it won't open all the way and will cause you to overboost. If you have an air compressor you can turn it down real low and see exactly how it reacts when pressure is fed to the actuator which helps identify issues and get it adjusted properly.

I think you hit it. The flappy door maf is worth like 4 hp on an NA car if you remove it. Its completely believable that it was creating just under a 2 psi pressure drop entering the turbo with the op flowing enough air to be making in the 180hp area.

+1. A MAF isn't much of a restriction, but an AFM is. This is a '91 car (AFM).

I am suspect of the wastegate actuator signal line though. Probably start there.

Good call on the MAF vs AFM, that is a significant difference.

Il take a picture of how everything is plumed and label everything.. Also I'm not running. Boost controller atm

Ok so I tested the wastegate and it works properly also tested the outlet from the turbo to the wastegate and it's also working properly

is your wastegate and boost gauge referencing from the same spot?

Reinstall your flappy door AFM without any wires hooked up and see if the overboost goes away.