Fuel cut problems 4g63T

[Blue Ice]

Well, it seems the only big problem is kind of a strange one.

At about cruising speed, and usually after about a minuite or so, the fuel cuts out majorly and the car runs horribly lean. if i accelerate, the car shakes uncontrollably. The only thing i can do is disengage the clutch and and let the engine idle back down. Then the ecu seems to reset the fuel ratio back to normal and i can get acceleration and cruise power back.

currently the fuel purge, and egr selonoids are unplugged. i think i'll plug them back in and see what happens.
Any other suggestions? I don't have the ecu chipped or socketed so i'm wondering what other adjustments i could make to pix this problem.

[kolio]

what size injectors are you running, and what turbo?

[seth98esT]

And is this under boost at all or just normal cruising?

[kolio]

also is it stock fuel pump and FPR?

[Blue Ice]

stock injectors and 14b. upgraded fuel pump and FPR, but again i only have problems at normal cruise. it runs a little rich when accelerating. I think my idle is set a lil high, but the A/F bounces back and forth in the yellow like it's supposed to. it's only when i'm cruising at a steady rate in 4th and 5th. the only way it will fix itself is by letting it fall all the way back down to idle. i can be rolling at about 65, but i have to pop it out of gear. wait about 10 seconds and then it's ok.

[Johnathansgalant]

maybe bad o2 sensor throwing trims off

[4-G-rim]

I did some research Lawrence and it could possible you have a Ecu with failing caps or the soldering of the sockets become loose over time and loose contact causing ECU issues like it were resetting.

Do you have access to swap your ECU with a known working ECU?

[DOHCstunr]

2g ecu's aren't really known for their problems.

have you done a boost leak test?
sounds like you are sucking in unmetered air.

[RafalGTZ00]

Sounds to me as though your fuel sensor isn't keeping up with the Turbo at higher cruise speeds. It's running lean because the turbo is pumping in extra air (like it always should) but the car's not expecting to need the power. When you try to accelerate fresh off that cruise point, the car actually approaches a stall as the air:fuel ratio goes even weaker. This wouldn't be a problem under a sustained acceleration because the injection system is expecting to dump in tons of gas. Dropping out to neutral dramatically decreases the amount of air being crammed into your cylinders by the turbo as a result of less exhaust from the idling engine, improving your fuel:air mix once again, until the car settles back into a sedate cruise mode.

[kolio]

what the hell are you talking about fuel sensor

thats what we have mafs for. they tell the ecu how much fuel to use

[4-G-rim]

Lawrence I would check for boost leaks. Check all your couplers in your i/c piping and make sure they are nice and snug. If you have access to for the home depot made boost leak tester..even better.

If that checks out I would swap ECU's and see if that fixes the issue. John is right that 2g ECU's aren't as prone to 1g ECU's for caps leaking..but they can still happen.

[DOHCstunr]

i thought it was Larry?

[seth98esT]

I had a 1g with a bad ECU, depending on where the caps were leaking, it could affect different things. I dont think this is your problem.

Definitely do a boost leak test. Do you have any logs when this happens? A WOT log and a log when this happens might help.

Id try swapping the MAF and the front o2 sensor first. If the front o2 sensor is bad, that would affect out of boost/WOT performance and not WOT performance.

[Blue Ice]

Sounds to me as though your fuel sensor isn't keeping up with the Turbo at higher cruise speeds. It's running lean because the turbo is pumping in extra air (like it always should) but the car's not expecting to need the power. When you try to accelerate fresh off that cruise point, the car actually approaches a stall as the air:fuel ratio goes even weaker. This wouldn't be a problem under a sustained acceleration because the injection system is expecting to dump in tons of gas. Dropping out to neutral dramatically decreases the amount of air being crammed into your cylinders by the turbo as a result of less exhaust from the idling engine, improving your fuel:air mix once again, until the car settles back into a sedate cruise mode.

ummm yes that's technically what is happening. Now i need to know how to fix it.

[Blue Ice]

i thought it was Larry?

It's both actually. :D

I had a 1g with a bad ECU, depending on where the caps were leaking, it could affect different things. I dont think this is your problem.

Definitely do a boost leak test. Do you have any logs when this happens? A WOT log and a log when this happens might help.

Id try swapping the MAF and the front o2 sensor first. If the front o2 sensor is bad, that would affect out of boost/WOT performance and not WOT performance.

Currently i have the front o2 sensor hooked up to the rear o2 connection which i did recently. But this problem has been happening since day one, and at first i didn't have the front o2 hooked up correctly, so there wasn't any readings from it at all.

As far as the cut off is concerned, it's not immediately. It usually happens after the cruise idle has been establishing for about 30 sec so i'm not sure where a boost leak would play into it all. i do know the ecu is looking for the MFI and my setup doesn't have it. i wonder how that plays into everything.

[mko]

Get the front O2 sensor hooked up correctly and see what happens. I had the same problem a few months ago, but only when the car was cold. It was the front sensor, and since Ive changed it I have no problems what so ever.

[Blue Ice]

i just thought about something John said a while back...

If the coolant wasn't going to the throttle body, then it won't close... well i have the hoses hooked up, but maybe it isn't getting there somehow... Wouldn't this effect the ratio during cruise?

[DOHCstunr]

i just thought about something John said a while back...

If the coolant wasn't going to the throttle body, then it won't close... well i have the hoses hooked up, but maybe it isn't getting there somehow... Wouldn't this effect the ratio during cruise?

that would only effect your idle. has zero bearing whatsoever at cruise, or at wot.

you could run with no o2 sensor at all and the only thing that is going to happen is that your ecu will be forced into open loop mode(the exact same mose that it operates under under any kind of load past 40% throttle.
so i doubt your o2 has anything to do with it.

the stock mas is good for over 400 hp. I highly doubt you are overrunning your mas.

I seriously think you are sucking in unmetered air.

is your BOV vented?


have you even done a boost leak test since assembly? a lot of spots that are boost leaks will also show their face as vacuum leaks.

[Blue Ice]

I think there may be an issue at the BOV. nop boost leak test. honestly don't know how to run one. But i'm pretty sure all thew hoses are good and tight except for the one around the larger BOV hole. and that one is hooked up to the return circulation. i'll look into that tonight.

[DOHCstunr]

do you have an air compressor? or access to one?
boost leak test is easy. One of the best ways to make your turbo scream like a damn banshee. and make sure your spoolup time and top end is where it should be.

tell me you've seen this page......
http://vfaq.com/index-main.html



specificly: http://vfaq.com/mods/ICtester.html

easy.