Fuel Cut: What is it? How do I fix it? [merged]

[Slanted J]

All fuel cut threads are combined here.

I've tried doing a search but to no avail.

I was just wondering what Fuel Cut is. I've heard it tossed around alot, but do not actually know the details behind it. And, naturally, I can gather that its when the fuel is cut off, but when and why.


Thanx,
Jon

 

[oldman]

I don't know what you mean by did I set the maf to blow through. Is there a different setting for if your maf is on the uicp or on the intake pipe? like do I have to change the intake air temp sensor or something? I thought that was part of the maf itself.
I set those four switches to off off off off if I remember correctly. But I thought the first two were for which size gm maf you have, while the latter were for rpm based wot tuning. what exactly do you mean by did I set the maf to blowthrough?

I'm not a maft user, I know that you can run it either in blow through or draw thought, I was under the inpression that you have to set it but I'm not sure, my appoligies if I'm wrong. In any case, are you reading 1600+ at 3500 rpm?

i am hitting fuel cut in second 3rd 4th and fifth gear on my 16g supra smic 1g in a 2g running 19 psi (cant run less due to creep) is this normal at all?

Have you boost leak tested?

 

[tstkl]

what does a fuel cut defencer actually do?

search for that answer, its something that prevents fuel cut. you should fix your creep problems before worrying about your fuel cut problems though

 

[tstkl]

I'm not a maft user, I know that you can run it either in blow through or draw thought, I was under the inpression that you have to set it but I'm not sure, my appoligies if I'm wrong. In any case, are you reading 1600+ at 3500 rpm?


Have you boost leak tested?

the logger cuts off at 1599 hz, but yes Im reading that

Im loading my logs onto my computer right now. for some reason it finally desided to work, so now I'm loading 48? logs and its taking forever...

 

[oldman]

the logger cuts off at 1599 hz, but yes Im reading that

Someone please verified whether there is a setting for blow through vs. draw through. If there isn't one, I would suggest swapping in another maf or reinstall your stock maf and see, 1600Hz at 3500 rpm with 14b @ 10psi doesn't sound right at all.

 

[tstkl]

Someone please verified whether there is a setting for blow through vs. draw through. If there isn't one, I would suggest swapping in another maf or reinstall your stock maf and see, 1600Hz at 3500 rpm with 14b @ 10psi doesn't sound right at all.

I did buy the maf used, there is no setting for blow through, and the fuel cut I was getting when the car was stock at 18 psi was on the old maf. once the logs are done I can find those logs probably, but again, there are 48 of them, so it may take a while. I know it was sometime last summer, but thats when the majority of them were taken. remember my car hasn't been running since august, so there were no logs between then and now.

 

[oldman]

You were probably hitting fuel cut with the old maf at 18psi because of boost leaks back then. How many psi did the intake hold during your last test at the TB elbow? Did you fix the intake manifold bolt?

I was serious about caps and punctuation, please don't make my job harder by being lazy.

 

[tstkl]

Sorry, but half of the time I don't notice when I'm not using proper grammer. I'll focus more now. I took it to paul and he is the person who fixed it. We pressurized it and it dropped slowly but 1) it was really slow, and 2) he only had this leaky boost leak tester, I'm surprised at how slow it leaked since it was leaking from the valve badly. I dont have an air compressor, I'll have to call around again and find someone who has one. By "holds 20 psi for 30 seconds" do you mean it doesn't drop below 20 psi for 30 seconds, or it doesn't drop below 0 psi for 30 seconds?

 

[oldman]

do you mean it doesn't drop below 20 psi for 30 seconds,

Hard to do but not impossible. My bov leaks at around 18psi, I can pressurize intake to about 26psi, takes about 20 seconds to leak down to about 17psi due to the BOV leak, from there it takes about 5 mins for it to bleed down to zero.

or it doesn't drop below 0 psi for 30 seconds?

Acceptable, assuming you're able to pump it up to 20psi.

 

[tstkl]

Hard to do but not impossible. My bov leaks at around 18psi, I can pressurize intake to about 26psi, takes about 20 seconds to leak down to about 17psi due to the BOV leak, from there it takes about 5 mins for it to bleed down to zero.


Acceptable, assuming you're able to pump it up to 20psi.

I know this may sound stupid, but I might as well make sure this isn't the cause. I have an open element filter on my valve cover. could this be the sorce of my leak?

this dodad \/

 

[oldman]

No, crankcase isn't a part of your intake tract but the filter on the the breather present another problem, is your pcv routed back to the intake manifold? Do you feel air coming out of the breather filter during the leak test?

 

[tstkl]

No, crankcase isn't a part of your intake tract but the filter on the the breather present another problem, is your pcv routed back to the intake manifold? Do you feel air coming out of the breather filter during the leak test?

There is a hose going from my intake manifold to the crankcase at the top by cylinder number 4, then this filter on it. I haven't looked to see if I can feel air coming out of that filter, but should there be?

btw the hotsync has been stuck on one log for the last like hour, so I'm going to try and kill it and start again.

Also, my bad, it was at 1599 hz at 3875 rpms, not 3500!!!!!(big whoop)

 

[oldman]

There is a hose going from my intake manifold to the crankcase at the top by cylinder number 4, then this filter on it.

I thought you have a SMIM? If your pcv is routed back to to the intake manifold, venting your breather to atmosphere will result in pcv pulling in unmetered air during idle or part throttle.

I haven't looked to see if I can feel air coming out of that filter, but should there be?

Air out of the breather during pressure test means intake pressure leaking into the crankcase via pcv, valve seals/guides or piston rings.

Also, my bad, it was at 1599 hz at 3875 rpms, not 3500!!!!!(big whoop)

Still way off.

 

[tstkl]

I thought you have a SMIM? If your pcv is routed back to to the intake manifold, venting your breather to atmosphere will result in pcv pulling in unmetered air during idle or part throttle.


Air out of the breather during pressure test means intake pressure leaking into the crankcase via pcv, valve seals/guides or piston rings.


Still way off.

If its letting in unmetered air at idle, that would cause the maf readings to decrease, and its a one way valve, right? So when pressure is built up, it does not escape through that filter does it? Basically I can use that filter to test if my pcv valve seals/guides or piston rings are holding, right? I dont care if I'm sucking in unmetered, filtered air at idle and mid conditions, since its so little I can compinsate for it, and thats not when the car is performing anyways.

 

[oldman]

If its letting in unmetered air at idle, that would cause the maf readings to decrease

That's why I said it's an unrelated issue.

and its a one way valve, right? So when pressure is built up, it does not escape through that filter does it? Basically I can use that filter to test if my pcv valve seals/guides or piston rings are holding, right?

Or you can just open the oil cap. I would like to see you re-do the leak test but focus on the cause of your fuel cut, incorrect MAF reading.

 

[tstkl]

That's why I said it's an unrelated issue.

Or you can just open the oil cap. I would like to see you re-do the leak test but focus on the cause of your fuel cut, incorrect MAF reading.

so basically do a pressure test and pay attention to my little filter and the throttlebody/smim area? ok, I'll make some calls and see how soon I can borrow an air compressor.

 

[tstkl]

took out the pcv valve and blew into it, it seems to hold pretty well.

finally got a hold of paul and this is what he said:
1, my car is actually running rich at idle, even though it says otherwise, because due to the crack in my manifold, air is being sucked in and throwing the afr off that the o2 sensor reads. 2, every maft he has used to tune has accurate base settings (everything zero'ed out) when they are in draw through, but every one he has tuned with that was in blow through was significantly off. He told me to lean it out and I should be good.

new fuel pump goes in, fuel at wot comes out. last time I checked it was .93v at wot, which is "rich as hell" according to paul. Everything seems to add up, I'll take some fuel away at idle (+20% vs +30%) and at wot (-10% to start)

will the vr4 fuel pump change my settings much (aka if I get everything dialed in then add the pump, will much change?)

 

[pneumo]

The fuel pump will not affect how rich the car runs, so don't change the settings.

 

[97_eclipse_gst]

Ok i have been having alot of problems with my car. In higher rpm's my car backfires very loud and the whole car shakes violently, and if i try to keep accelerating it usually continiously backfires. I have tried so many different things to fix this. It has gotten better but it still continues to backfire. I am running 15lbs of boost on the stock t25, can this still be fuel cut? Any input would be very very helpful.

Also if it is fuel cut would a dsm-link help me prevent it?

 

[ALLBoostAWD]

Sounds like its Detinating, check your timing.

 

[ALLBoostAWD]

if you dont have one yet, and think it is fuel cut; buy this.

http://cgi.ebay.com/ebaymotors/ws/e...PageName=MERC_VI_ReBay_Pr12_PcY_BIN_Stores_IT

 

[oldman]

Boost leak test and check plugs and wires. I don't think you are hitting fuel cut, sounds more like bogging to me, either way fixing boost leaks will fix both.

 

[oldman]

if you dont have one yet, and think it is fuel cut; buy this.

http://cgi.ebay.com/ebaymotors/ws/e...PageName=MERC_VI_ReBay_Pr12_PcY_BIN_Stores_IT

Bad idea, nothing but a bandage to the real problem.

 

[DSMcamaro]

if you dont have one yet, and think it is fuel cut; buy this.

http://cgi.ebay.com/ebaymotors/ws/e...PageName=MERC_VI_ReBay_Pr12_PcY_BIN_Stores_IT

What oldman said and he has a 2G so it would be even more of a waste of money.

 

[crxp-o-s4now]

Same thing happened to mine. Re-gap plugs/check wires.

 

[pecka]

Same thing happened to mine. Re-gap plugs/check wires.

Yeah me too. Mine needed new plugs, I thought the damn thing was hitting fuel cut, but it was trying to do it no matter what rpm, then I realized it. Some new bpr6es and it was all fixed.