hitting fuel cut at 10psi
09-07-08, 12:43 PM
#1
hitting fuel cut at 10psi
hey guys i fixed my ECU cel codes, got the car running great back on the stock ECU, but now i'm hitting fuel cut in the high RPMs and i'm only running 10psi.
it really feels like i'm overboosting, but i'm not, and i T'd my boost gauge into the same line as the MAP sensor just to make sure i was reading the correct boost.
1st gear doesn't hit fuel cut
2nd gear hits fuel cut at about 7000rpms
3rd gear hits fuel cut at about 6500rpms
anyone else have this problem? i'm really confused.
it really feels like i'm overboosting, but i'm not, and i T'd my boost gauge into the same line as the MAP sensor just to make sure i was reading the correct boost.
1st gear doesn't hit fuel cut
2nd gear hits fuel cut at about 7000rpms
3rd gear hits fuel cut at about 6500rpms
anyone else have this problem? i'm really confused.
09-07-08, 04:06 PM
#2
Racecar - Formula 2000
Have you calibrated your boost gauge? Maybe it's reading a few psi low?
09-07-08, 07:02 PM
#6
For years, the "gurus" on this site have preached that you can run as many mods as you want on the stock ecu, as long as you do not exceed 10 psi. If that is true, your boost gauge is wrong, you are not hitting fuel cut, or you have some other issue.
If you have a boost controller, I would dial it back to 8 psi, and see if your problem goes away.
If you have a boost controller, I would dial it back to 8 psi, and see if your problem goes away.
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09-08-08, 12:32 PM
#10
actually i have a prosport mechanical boost gauge, which isn't the highest quality, but matched the reading on both my haltech (3bar GM) and powerFC MAP sensors nearly perfectly.
from what i've seen of the stock ECU's plotting of fuel cut for overboosting, above 6500rpms it cuts fuel at 10.7psi, so even a slight variation in MAP reading and boost gauge reading could be causing the confusion.
i guess the best solution, while not having to deal with the standalones or the stock ECU, would be to get a pettit ECU.
09-08-08, 12:36 PM
#11
ChumpCar**Apex of Failure
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I had this exact problem. I'm not sure its resolved yet. I think my problem was one of the caps I had put on the wastegate was starting to leak. Check your vacuum lines on your boost control system.
09-08-08, 08:47 PM
#12
i had a similar problem...im using manual boost controllers and 1st and 2nd wot was great but 3-4-? above 6k rpms would hit fuel cut. Boost controller showed rock solid 9-10 psi. I dialed the controllers down a little and it solved my problem. Now its 8-9 psi with no fuel cut what so ever in any gear. I have a autometer boost gauge and figured it was off a psi or two
09-08-08, 11:55 PM
#14
No. The issue is how much fuel the stock system can provide, and for how long. In 1st and 2nd gear, high rpm is reached very quickly, and is not sustained for more than a second or two. In third and higher gears, it takes much longer to reach redline. That means that more fuel is needed for a longer period. The stock ecu can't/won't provide high volumes of fuel for very long because it thinks it needs to protect the engine. That's why it has a fuel cut built in, and that's why you hit it earlier in higher gears.
09-09-08, 05:44 PM
#15
i was doing some more investigating today and noticed that the fuel cut happens regardless of PSI.
the ECU was cutting fuel at 7000rpms in second at 7psi. yes, 7psi.
same thing in 3rd, except it was at about 6500 rpms.
i am now quite confused.
the ECU was cutting fuel at 7000rpms in second at 7psi. yes, 7psi.
same thing in 3rd, except it was at about 6500 rpms.
i am now quite confused.
09-10-08, 03:43 AM
#18
Rotary for life!
I was just about to make a thread with a similar problem i've got. Mine seems to cut out at 7500rpm at every gear as if it's hitting fuel cut... it hits 7500rpm, then RPM's just decrease. Only running 10psi with intake and exhaust running stock ECU...
09-10-08, 09:20 AM
#19
Racecar - Formula 2000
I'm starting to think you have a fuel supply problem, not fuel cut. How long since you changed the fuel filter? Do you know what pressure your fuel pump is putting out?
09-10-08, 09:28 AM
#20
ChumpCar**Apex of Failure
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Is there a stock fuel pressure sensor? Is there anyway to test to make sure you are getting fuel delivered properly without hooking up a gauge?
I think I have the same problem. My injectors were cleaned and tested by RC, did the fuel recall kit, replaced the fuel pulsation damper, and replaced the fuel filter ~4,000 miles ago. There aren't many parts left
. Maybe the fuel pump is starting to go. How long do fuel pumps normally last?
I think I have the same problem. My injectors were cleaned and tested by RC, did the fuel recall kit, replaced the fuel pulsation damper, and replaced the fuel filter ~4,000 miles ago. There aren't many parts left
. Maybe the fuel pump is starting to go. How long do fuel pumps normally last?
09-10-08, 11:37 AM
#21
1. i have a wideband in the car, which indicates that i'm running high 10's/low 11's AFRs in boost until the fuel cut happens. the car runs perfectly fine, is not lean, and is very smooth until the fuel is cut.
2. i have a fuel pressure gauge in the car, which indicates that i'm holding a steady fuel pressure -fuel pressure 55-60psi, dependent on what boost i'm running- with no drop off from the pump when the cut out happens.
one would think that those two tools would let me know if i have a fuel supply problem.
Is there a stock fuel pressure sensor? Is there anyway to test to make sure you are getting fuel delivered properly without hooking up a gauge?
I think I have the same problem. My injectors were cleaned and tested by RC, did the fuel recall kit, replaced the fuel pulsation damper, and replaced the fuel filter ~4,000 miles ago. There aren't many parts left. Maybe the fuel pump is starting to go. How long do fuel pumps normally last?
I think I have the same problem. My injectors were cleaned and tested by RC, did the fuel recall kit, replaced the fuel pulsation damper, and replaced the fuel filter ~4,000 miles ago. There aren't many parts left
. Maybe the fuel pump is starting to go. How long do fuel pumps normally last?Last edited by jacobcartmill; 09-10-08 at 11:45 AM.
09-10-08, 11:46 AM
#22
Racecar - Formula 2000
i'm curious as to your rationale behind thinking that i have a fuel supply problem. this isn't like my engine is gradually leaning out and finally resulting in a lean cut-out, this is hitting a wall of fuel cut, in which my car abruptly is cut of all fuel. have you ever over boosted on your stock ECU and hit fuel cut? i have, several months back, and it feels exactly the same as what's happening now, except that i'm not overboosting.
1. i have a wideband, which indicates that i'm running high 10's/low 11's AFRs in boost until the fuel cut happens. the car runs perfectly fine, is not lean, and is very smooth until the fuel is cut.
2. i have an in-car fuel pressure gauge, which indicates that i'm holding a steady fuel pressure -fuel pressure 55-60psi, dependent on what boost i'm running- with no drop off from the pump when the cut out happens.
one would think that those two tools would let me know if i have a fuel volume problem.
fuel pumps start getting weak before they die (usually), which will drop your fuel pressure and lean your AFRs out. you'd know if your fuel pump was getting weak while boosting because you'd probably have a blown motor and wouldn't have to worry about AFRs anymore. you probably don't have a fuel volume problem.
i didn't start this thread to inform people how fuel volume works on a boosted internal combustion engine. i started this thread to see if anyone knew why a stock ECU would cut fuel at different RPM points based seemingly on engine load and not on boost alone.
1. i have a wideband, which indicates that i'm running high 10's/low 11's AFRs in boost until the fuel cut happens. the car runs perfectly fine, is not lean, and is very smooth until the fuel is cut.
2. i have an in-car fuel pressure gauge, which indicates that i'm holding a steady fuel pressure -fuel pressure 55-60psi, dependent on what boost i'm running- with no drop off from the pump when the cut out happens.
one would think that those two tools would let me know if i have a fuel volume problem.
fuel pumps start getting weak before they die (usually), which will drop your fuel pressure and lean your AFRs out. you'd know if your fuel pump was getting weak while boosting because you'd probably have a blown motor and wouldn't have to worry about AFRs anymore. you probably don't have a fuel volume problem.
i didn't start this thread to inform people how fuel volume works on a boosted internal combustion engine. i started this thread to see if anyone knew why a stock ECU would cut fuel at different RPM points based seemingly on engine load and not on boost alone.
Well, now with the fuel pressure data (which I didn't know before), I'm somewhat baffled, also.
The stock ECU fuel cut does have a time delay built in, which usually results in fuel cut mostly in the higher gears due to the longer time at higher boost. but the cut at low boost levels is confusing.
Dave
09-10-08, 11:54 AM
#23
Well, now with the fuel pressure data (which I didn't know before), I'm somewhat baffled, also.
The stock ECU fuel cut does have a time delay built in, which usually results in fuel cut mostly in the higher gears due to the longer time at higher boost. but the cut at low boost levels is confusing.
Dave
The stock ECU fuel cut does have a time delay built in, which usually results in fuel cut mostly in the higher gears due to the longer time at higher boost. but the cut at low boost levels is confusing.
Dave
yeah i did a little research about the fuel cut several months back when i was overboosting, and it seems that there's about a 1/2 second delay, which i suppose is built in for quick and minor boost spikes.
until yesterday i was pretty convinced that i just wasn't watching the boost gauge closely enough, and thought i was just barely hitting the fuel cut. yesterday, though, i turned the boost down and it did the exact same thing at 7psi. i even did another pull to make sure the boost was staying steady and not shooting up at the last split-second before the cut-out.
i had to re-wire the plug for my crank trigger, as when i got my harness one of the wires was broken, so i thought that could be the problem, but i think that would make a static change in the RPM signal that wouldnt be affected by different levels of load.
09-10-08, 12:17 PM
#24
Racecar - Formula 2000
The only other thing that occurs to me is a wiring issue from the MAP sensor causing the ECU to think the boost is higher than it actually is. Either that or your boost data sources are not seeing full boost pressure, which, given your modifications, makes some sense, since you should be seeing more than 10 psi boost.
Dave
Dave
09-10-08, 04:51 PM
#25
The only other thing that occurs to me is a wiring issue from the MAP sensor causing the ECU to think the boost is higher than it actually is. Either that or your boost data sources are not seeing full boost pressure, which, given your modifications, makes some sense, since you should be seeing more than 10 psi boost.
Dave
Dave
i have done the full non-sequential mod, i have a MBC controlling my boost (up from the base 7psi wastegate spring) and i have my boost gauge T'd into the MAP sensor line, so they see the same signal.