Fuel cut or fuel starvation?

snowboarded · Post by **snowboarded** » Tue Oct 18, 2005 1:54 pm

So it has been happening very consistently now (about 4 times a day for the past week) so I know its not a fluke.

I am pulling hard in 3rd or in 5th in a straight line with no turns recently made I am hitting 15 plus psi on the gauge. That will last for a few seconds and then bam, no go for about a second and then it picks back up it spikes again then no go twice, once when it hits 15 psi and then again falling down when it hits 13 1/2. What the heck is happening? I don't have my ebc installed yet and don't have the ic on. How am I consistently surpassing stock boost levels? And is this fuel cut or fuel starvation as in my injectors or pump can't handle these levels? Or is it both?

vrg3 · Post by **vrg3** » Tue Oct 18, 2005 3:46 pm

This is almost certainly fuel cut. The ECU's trying to protect the engine from this overboost condition.

So you're hitting 15 psi with stock boost control? Clearly something ain't right... maybe you should check the boost control hoses.

http://www.graphics.cornell.edu/~v/vacuum/

Make sure the hoses are properly seated and not clogged or anything.

Richard · Post by **Richard** » Wed Oct 19, 2005 5:48 am

Wow. 15 lbs on a stock turbo??? What are you doing now to prevent detonation?

snowboarded · Post by **snowboarded** » Wed Oct 19, 2005 1:30 pm

For the time being, Taking my foot off the gas when I see it hit 13.

555BCTurbo · Post by **555BCTurbo** » Fri Oct 21, 2005 8:57 pm

I am running more than 15 psi on a stock turbo and my car doesn't detonate...granted I do have a walbro 255lph pump...

tris91ricer · Post by **tris91ricer** » Thu Nov 24, 2005 1:50 pm

Sorry to ressurect this one, but my issues now are similar.

I'm hitting about 10psi max, and whether I let off the go-pedal or not, boost drops back into vaccuum and then pops up again.

Granted, my boost is lower, and I'm running about 9:1 on an ej20g with legacy turbo heads. Stock internals, stock turbo.
I am told there's slight detonation, although not only am I completely unfamiliar with what it is or sounds like, I doubt I'd be able to hear it --my gears are also loud.
So my question now is: does a walbro 255lph fuel pump help alleviate my detonation? Perhaps that combined with a rrfpr? I have plans to intercool, but I'm still undecided on what I want for that. I have no compunction about f-ing my firewall, though, so maybe a wrx ic is the way to go, eh?

555BCTurbo · Post by **555BCTurbo** » Thu Nov 24, 2005 8:02 pm

I would say do the same setup I have:

Walbro Pump
AWIC
FCD (either MAP bleed or VRG3 FCD)
Adjustable or Rising Rate FPR

Your compression ratio is going to limit your possibilites as far as boosting because it is in N/A motor territory, and if you cram too much air down it's throat you are going to get hot spots=detonation=motor go boom.

I would say that you could safely run 12psi with the mods I suggested above, and maybe get a Wideband O2 Sensor to watch the AFR when on boost, so that you can visually see when the motor will be prone to detonate.

Hope this helps

tris91ricer · Post by **tris91ricer** » Fri Nov 25, 2005 6:40 pm

So does detonation mean I'm not getting enough fuel, and that I'm getting too much air? Like I said, I wasn't sure what detonation really was.

555BCTurbo · Post by **555BCTurbo** » Sat Nov 26, 2005 2:17 am

Detonation is the product of uneven combustion... Hot spots in the combustion chamber ignite before the rest of the compressed mixture, resulting in preignition and small, damaging explosions...

Basically, the rule of thumb is that detonation happens when you don't have enough fuel, i.e. too much boost without the adequate amount of fuel. Soo...If your car makes a small, metallic ping sound under acceleration, it is most likely detonating, and if this happens, get out of the throttle!!

rallysam · Post by **rallysam** » Sun Nov 27, 2005 5:59 pm

tris91ricer wrote:Sorry to ressurect this one, but my issues now are similar.

I'm hitting about 10psi max, and whether I let off the go-pedal or not, boost drops back into vaccuum and then pops up again.

Granted, my boost is lower, and I'm running about 9:1 on an ej20g with legacy turbo heads. Stock internals, stock turbo.
I am told there's slight detonation, although not only am I completely unfamiliar with what it is or sounds like, I doubt I'd be able to hear it --my gears are also loud.
So my question now is: does a walbro 255lph fuel pump help alleviate my detonation? Perhaps that combined with a rrfpr? I have plans to intercool, but I'm still undecided on what I want for that. I have no compunction about f-ing my firewall, though, so maybe a wrx ic is the way to go, eh?

How do you know you are at 10psi? FWIW, I thought I was getting fuel cut at 10psi. Turns out my autometer boost is reading wrong and I was actually at 13 psi where the ECU SHOULD be cutting fuel.

tris91ricer · Post by **tris91ricer** » Sun Nov 27, 2005 9:13 pm

It was only cutting fuel under boost, and that was when I didn't have a boost guage.

Now, with the autometer, its saying I'm just under 10psi, which to me, would equate to ~stock boost levels.

I just picked up a wrx ic last night, and I've already got the y-pipe to go with it, so I think I'll be looking into whether or not intercooling will help solve my problem. I may just turn the boost down anyway.

I did try some octane booster last night. I used the 104 street formula. Not bad at 8.99 a bottle, but it still didn't prevent detonation, I don't think. Note: when I say I'm getting detonation, I assume that's what the CEL comes on for after I boost.
(Pulling the codes on it last time revealed a 12 24 33 45. ) I gotta check the table again, but some of these codes aren't necessarily boost related.

So, should the intercooler help? Anyone got ideas for the plate I need (on the ic) to continue using the stock recirc valve?

rallysam · Post by **rallysam** » Sun Nov 27, 2005 10:09 pm

I know your autometer says 10psi. I'd suggest you use the VRG3 scan tool to see what boost the ECU is actually seeing and using. The ECU's pressure sensor could be wrong or your autometer could be wrong.

If the ECU also sees 10psi, then I'd say fuel cut is due to a different issue.

Intercooling shouldn't change the boost-based fuel cut, if that really is your issue. Of course, it might fix the problem inadvertantly by lowering the pressure a tad, but that's not really getting to the bottom of the issue.

On the plate for the stock recirc valve, VRG has cooked up a flange and elbow based on hardware store parts. I have pictures of it in my IC install thread. For a more spanky solution, you can get a purpose-built flange and 90 degree below from TurboXS, then connect the elbow to your recirc valve with some clever silicone tubing work.

Threshld1 · Post by **Threshld1** » Fri Dec 30, 2005 5:58 pm

Along those lines i am running a MBC ball/spring setup i made and im pushing ~13.5psi peak with it fading down slightly to about 11 on my 93 SS stock
When i hit fuel cut the few times setting this thing up (always in 3rd or higher) it just blipped out with no CEL. Is the CEL supposed to come on or might i have a bad light?

tris91ricer · Post by **tris91ricer** » Fri Dec 30, 2005 8:21 pm

Ball and spring is the usual mbc, as I understand it. I would pull your codes to find out what condition your CEL is in. . . If it still flashes, I'd guess its okay.

Maybe I should continue my saga from here, instead of making a new thread.

Basically, I'm down to two codes left to solve, 24 and 33.

24 is the vss, or the Vehicle Speed Sensor. The cable inside the extension (that comes right off the tranny) broke (twisted off, probably due to age.) So I'm just going to get a new speedo cable --from the extension to the back of the cluster-- and be done with it. Taking out the cluster isn't that hard anymore. . .

My problem, however, lies with the code 33, which, according to Josh's table, is the Air Control Valve. Wtf is this? I'm not even sure what this is or does. I do notice one thing, though, and its air-related:

Under boost, I was on the assumption that the ecu will not let you push past 5psi. My boost gauge tells me I'm still coming quite close to 10psi. What's it doing with this excess air, on-throttle? I know its not getting recirc'd, I'd hear it. So could that be part of the problem? That its boosting 10 when its only supposed to be 5?

Also, has anyone else had these two codes come out and stick concurrently?

Post by **Legacy777** » Sat Dec 31, 2005 12:18 am

You got the codes backwards

24 is the air control valve
33 is the vehicle speed sensor

The air control valve is the idle air control valve.

tris91ricer · Post by **tris91ricer** » Sat Dec 31, 2005 1:07 am

Legacy777 wrote:You got the codes backwards

24 is the air control valve
33 is the vehicle speed sensor

The air control valve is the idle air control valve.

*blush*

I was born blonde, this is true.

So uh. . . . Yeah, dammit. I didn't wanna hafta mess with that. Please! Anything but the IAC valve! ! ! !111

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Fuel cut or fuel starvation?

Fuel cut or fuel starvation?