Hitting Fuel cut/inconsistant boost!

1275 Views 26 Replies 9 Participants Last post by Maverick31, Nov 22, 2005

Maverick31

Discussion Starter · Nov 19, 2005

I have fuel cut turned off(using the translator), and the damn thing still hits it!
Also, I can't keep my boost steady for the life of me. I check for boost leaks, and nothing turns up... I tested up to 30psi.
Could this be symtoms of a bad GM MAF? I mean, I just don't know what it could be anymore. I also get terrible boost spike, and the boost always drops off after 5000rpm in every gear. The fuel cut seems to happen most often when in overdrive and flooring it. Its holding around 19psi or so(until 5K, then 17). It also sometimes happens in 3rd.
I tried adding more fuel, but it seems to get worse, so I lean it back out.
Also, my car stalls when I rev it in P or N.
Please help me guys!

My mods are:
EvoIII 16G turbo(ported, 34mm Wastgate flapper), MHG, 3 inch tig welded turbo-back exhaust, 450cc injectors, Supra TT fuel pump, WAI, Man. boost controller, Evo 3 Exhaust manifold(ported 7cm), M/T ECU, Slow-Boy Racing tubular O2 housing, Fully gutted out, GM 3" MAF, MAFT, 3" Intake Pipe, Magnacore 8.5mm wires, 3rd Gen Revised Lifters, Dejontool Compressor Elbow,Extreme FMIC kit, IPT A/T "Boost Controller". IPT Custom High Stall TQ Converter, NGK (7's)plugs.

1 - 20 of 27 Posts

Maverick31

Discussion Starter · #2 · Nov 19, 2005

And just to explain the inconsistant boost levels a bit more, this is what happens:

1st- Spikes to 21-22psi, then down to 16psi, then right before its time to shift, 17psi.

2nd- Spikes to 21 psi, then down to 19psi, then at exactly 5000rpm it drops to 17psi.

3rd- Spikes to 20psi, then down to 19psi, then at exactly 5000rpm, its drops to 17-18psi.

4th(OD)- Spikes to 21, then down to 19.5 psi, until 5000rpm, then it drops to 18psi.

I have been trying to figure this out for a long time. Keep in mind that there is no boost leaks, I tested it to 30psi.

Dyesin

· #3 · Nov 19, 2005

Do you have a logger?

Maverick31

Discussion Starter · #4 · Nov 19, 2005

No, but I just ordered a PLX wideband to help tune it. That should be here tuesday.

dsmbuilder

· #5 · Nov 19, 2005

Sounds like you are not hitting fuel cut, but overrunning those 450's. Get some 650's for that thing.

Maverick31

Discussion Starter · #6 · Nov 19, 2005

How about 550's? If 650's are better, find me some cheap!

But whats up with the fluxuating boost levels? It drops boost at EXACTLY 5000rpm in every gear. Thats the only consistant my car does.

Maverick31

Discussion Starter · #7 · Nov 20, 2005

Ok I just bought 650cc's.
You guys think what I'm getting is NOT fuel cut though?

DRSully

· #8 · Nov 20, 2005

I am not 100% sure, but I would agree that you need more fuel. Tune again with the 650's and keep us updated.

Take care,

David

Maverick31

Discussion Starter · #9 · Nov 21, 2005

Well, even if it is fuel cut, lack of fuel could cause that, right?
I mean, if I'm bringing in too much air without having the ability to compensate with fuel, it would make sense that it would cause fuel cut.

Maverick31

Discussion Starter · #10 · Nov 21, 2005

But what could be causing fluxuating boost and stalling?
Could maxing out injectors do that?

DRSully

· #11 · Nov 21, 2005

Maverick31 said:
But what could be causing fluxuating boost and stalling?
Could maxing out injectors do that?

I believe so. I believe you could be hitting fuel cut, because not enough fuel is present. You would be running extrememly lean which would cause knock retard. You might be running lean enough to the point where stalling is possible. All of the air with no fuel might also be causing the boost problem. I am 100% sure that you need more fuel. You may have already caused damage by running the way you are. I am sure the duty cycle on your injectors is scary. Wait for the 650s before you do anything else.

Take care,

David

Maverick31

Discussion Starter · #12 · Nov 21, 2005

Thanks man.
I think I'll just turn down the boost to like 14-15psi for now. My wideband should be here by tuesday, and I ordered the 650's yesterday. I'm ready to get this car running right! You don't think it will be that hard to tune 650 injectors using the MAFT, do you?

DRSully

· #13 · Nov 21, 2005

Maverick31 said:
Thanks man.
I think I'll just turn down the boost to like 14-15psi for now. My wideband should be here by tuesday, and I ordered the 650's yesterday. I'm ready to get this car running right! You don't think it will be that hard to tune 650 injectors using the MAFT, do you?

Plenty of people do it. I think it is easier with a SAFC to fine tune, but people have proven that you can get by with just the MAF-T.

Take care,

David

Maverick31

Discussion Starter · #14 · Nov 22, 2005

Thanks a lot man!

Someone just told me that I'll have to use another piggy back unit to prolong fuel cut, that the MAFT won't do the job. Is this true? I would hate to spend more money on a SAFC2 or something if I don't have to.

DRSully

· #15 · Nov 22, 2005

Maverick31 said:
Thanks a lot man!

Someone just told me that I'll have to use another piggy back unit to prolong fuel cut, that the MAFT won't do the job. Is this true? I would hate to spend more money on a SAFC2 or something if I don't have to.

This is an argument that I am seeing in several threads. It is possible to tune with just the MAFT. Plenty of people do it like this. I would not myself. I would at least add a SAFC. I plan on using DSMlink in the future myself. Do some searching, and you will see that the opinion is pretty well split on this one.

Take care,

David

thegreatms

· #16 · Nov 22, 2005

DRSully said:
I believe so. I believe you could be hitting fuel cut, because not enough fuel is present.

This is incorrect. Oddly enough you do not hit fuel cut from to little fuel. It has NOTHING to do with fuel/injectors/fuel pump. It has everything to do with AIRFLOW. When your airflow gets high enough the ecu thinks that your injectors are about to max-out and destroy your engine from a lean condition (note it doesn’t matter whether your engine is in fact lean or rich). The ecu then tries to save your engine by cutting all fuel for a few seconds. Fuel cut will feel like your engine just blew up, or like the car hit a brick wall; it is very violent.

The problem is that the ecu is often wrong with a modified car. Either it does not signal fuel cut and you car goes lean and puts a hole in a piston. Or it thinks the car is flowing too much air and cuts all fuel when you were in fact running a conservative A/F ratio.

To OP:
Describe what you call “fuel cut” in more detail. I have a feeling you are not getting it.

Remember there is a different between fuel cut and overrunning your injectors. Fuel cut is a safety measure to stop you from overrunning your injectors.

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Maverick31

Discussion Starter · #17 · Nov 22, 2005

Feels like I hit a brick wall.
But if I turned off fuel cutt using my translator, why is it still happening? What do I have to do to fix this?

Maverick31

Discussion Starter · #18 · Nov 22, 2005

What is it suppose to feel like when you overrun your injectors?

thegreatms

· #19 · Nov 22, 2005

Maverick31 said:
What is it suppose to feel like when you overrun your injectors?

Well if you do it bad, the A/F will go way too lean, and stuff will start melting. Do you have a logger? that will give you injector pulse width.

Tenacious-B

· #20 · Nov 22, 2005

Maverick31 said:
What is it suppose to feel like when you overrun your injectors?

If you're unlucky it will feel like a lot of money flowing out of your wallet as you spend it on a motor rebuild. As noted above, get your hands on a logger.

1 - 20 of 27 Posts

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