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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. |
Have you calibrated your boost gauge? Maybe it's reading a few psi low?
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That used to happen to me in 4th and 5th gear back when I was mostly stock with exhaust... not sure what it was, but it felt like hitting a wall, thought maybe it was detonation. But I don't know.
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Mods???
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intakes/DP/MP/2.5" catback
those mods would suggest boost creep, but i can literally watch the boost gauge and it doesn't more past 9-10 psi even at higher load. i suppose it could be slightly off |
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. |
Try switching MAP sensors, too.
Dave |
My guess is you have a "Autometer" boost gauge.
Paul |
I had the same problem a while back. I know it's old news, but my only suggestion would be a pettit flash. Worked for me and I was quite happy with it.
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Originally Posted by Gadd
(Post 8533625)
My guess is you have a "Autometer" boost gauge.
Paul 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. |
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.
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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
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Does the stock boost control system have some per gear control in it or something?
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Originally Posted by parid
(Post 8536802)
Does the stock boost control system have some per gear control in it or something?
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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. |
so what were your CEL codes? And was this a swapped ECU or did it work perfect before?
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it worked perfectly before. the only codes i have are for airpump and a couple other emissions solenoids.
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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...
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Originally Posted by jacobcartmill
(Post 8539471)
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. |
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? |
Originally Posted by DaveW
(Post 8541335)
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?
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.
Originally Posted by parid
(Post 8541348)
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? |
Originally Posted by jacobcartmill
(Post 8541713)
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. 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 |
Originally Posted by DaveW
(Post 8541743)
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 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. |
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 |
Originally Posted by DaveW
(Post 8541825)
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 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. |
Originally Posted by jacobcartmill
(Post 8542654)
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.
Dave |
Have you checked the MAP to see if was in spec? If it is, than I'd revisit the repairs you have made to the crank sensor. The oem wiring is shielded from the crank to the ecu because it needs a clean signal from the CAS. I've seen all sorts of aberrant behavior from motors that were getting poor signals to the ecu from damaged wiring.
Paul |
i just wanted to update this thread.
i found my long-lost mity-vac vacuum/boost tester and i tested my MAP sensor. the sensor is stuck at 5.0V no matter what vacuum/boost it sees. SO, the sensor is dead and it is making my ECU think it's runng 17psi, hence the fuel cut :) apparently, before, i was testing wires A and C and should have tested A and B. thanks for the help guys |
That's good to hear.
Hopefully you don't have too much pent-up frustration to deal with. Dave |
i spoke too soon!
the sensor tested bad, so i replaced it with a known good sensor and the problem is still the exact same......... i'm not sure where to turn to now. |
here is my list of CEL codes:
5 - knock sensor 25 - PRC solenoid 28 - EGR solenoid 30 - split air bypass 31 - relief 1 solenoid 32 - switching solenoid 33 - port air bypass 34 - idle speed control 38 - AWS solenoid 39 - relief 2 solenoid 42 - turbo precontrol solenoid 46 - charge relief solenoid 50 - double throttle control solenoid I don't see how any of those could make me hit fuel cut under 10psi! |
another update. i just installed a known-to-be-good ISC and reset the ECU and the code didn't go away...
i am starting to think it is this crappy wiring harness... |
The ECU usually throws codes based on incorrect resistance.
I would take a sensor that's throwing a code, check it's resistance alone, then check it's resistance through the wiring harness at the ECU. Dave |
Try connecting your boost gauge to the nipple on the passenger side of the intake instead of Teeing it into the MAP line and see if you get different boost readings when you hit the fuel cut. And while you're at it, use the Mighty-Vac to test your boost gauge if you haven't done that yet. Hook the M-V up to the boost gauge hose at the point where the hose connects to the engine in order to ID any leaks in that line.
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when the knock sensor isn't present.. does it show max knock? min knock? or something between?
would excessive knock cause the car to fuel cut as a safety measure? do you or a nearby friend have a power FC to test with? it's my understanding then when cancelling the rats nest.. you HAVE to put resistors and not have codes |
Originally Posted by Ottoman
(Post 8759762)
when the knock sensor isn't present.. does it show max knock? min knock? or something between?
would excessive knock cause the car to fuel cut as a safety measure? do you or a nearby friend have a power FC to test with? it's my understanding then when cancelling the rats nest.. you HAVE to put resistors and not have codes yeah that's a good idea with the powerFC. i suppose that will have to be my next step. that's correct about having to put resistors in to avoid codes, but codes don't cause fuel cut, they cause limp mode (and only certain codes at that). apparently the only thing that causes over-boost fuel cut (exactly what this feels like) is the map sensor reading too high... |
Originally Posted by Retserof
(Post 8759501)
Try connecting your boost gauge to the nipple on the passenger side of the intake instead of Teeing it into the MAP line and see if you get different boost readings when you hit the fuel cut. And while you're at it, use the Mighty-Vac to test your boost gauge if you haven't done that yet. Hook the M-V up to the boost gauge hose at the point where the hose connects to the engine in order to ID any leaks in that line.
i have done all of the things you mentioned. i also moved my boost/vac source for the boost gauge from the passenger side over the the drivers side, then tee'd it off of the MAP signal so i could see what the map was seeing. the boost guage is reading correctly. it is also worth mentioning that the fuel-cut happens regardless of boost pressure. it will do the same thing at 6psi that it does at 12psi. |
So you're measuring an excessively high voltage on the MAP signal wire... try measuring the MAP signal pin on the ECU (key on engine off), measure it with the sensor plugged in and then with the sensor disconnected.
If you measure 5V at the ECU even when the sensor is disconnected, try measuring the MAP signal wire again at the MAP sensor connector. If you measure 0V at the sensor connector but 5V at the ECU, it's likely you have a break in the signal wire somewhere. Many ECUs have a circuit inside them that will cause the signal wire to measure 5V at the ECU if the sensor is not connected, I'm not sure if the stock RX7 ECU has a circuit like this or not. |
i repaired and re-wrapped the entire engine wiring harness, hooked everything back up and it still hit the "fuel cut." apparently i still had the knock sensor wire disconnected. I connected the knock sensor wire and it totally went away.
i put resistors in all the emissions solenoids and hooked the knock sensor up and i have no CELs and the car runs perfectly. |
So with the entire harness repaired and with a disconnected knock sensor, you would hit fuel cutout.
Reconnect the knock sensor and everything runs fine. Sounds like the FSM might not be telling the whole story. Was the knock sensor working properly before the harness repair? |
yes it was.
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I know this sounds simple, but have you tried swapping out your ecu with a friend's?
Long ago, I was working on my FD w/ the battery cables still in place (dumb i know). I accidentally touched the alternator and the ground with a wrench and there was a short. Car started up fine, everything seemed normal. Took her for a ride when i was done w/ my project and the car would hit boost cut almost immediately. Swapped out the ECU w/ a friend's, problem solved: My ecu was fried and it exhibited no symptoms other than the boost cut. Give it a try (if you haven't already). |
yep. tried that.
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Well sounds like you fixed the problem by redoing the wiring harness. Nice work! I have a feeling that might be on my list of projects in the future based on the condition of some of the wires I've checked. Hard for me to shell out almost a grand for a new one...
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really the problem the entire time was the stupid knock sensor!
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Originally Posted by jacobcartmill
(Post 8785717)
really the problem the entire time was the stupid knock sensor!
Dave |
yes that's correct. it has been disconnected since i went back to the stock ECU/harness/coils. (sold my haltech e8 and went back to stock)
however, i did repair SEVERAL wires that were broken or about the break off at the base of their plug (sensor side of harness) and repaired several very weak grounds. prior to this i had a minor 2k rpm hesitation and that is now gone. My ISC valve was also not functioning due to bad wiring. also i got rid of EVERY ECU CEL code :) so i guess it's a good thing that this turned into an involved project, because i've pretty much got a brand new wiring harness now and everything is working as it should. |
Originally Posted by jacobcartmill
(Post 8785764)
yes that's correct. it has been disconnected since i went back to the stock ECU/harness/coils. (sold my haltech e8 and went back to stock)
however, i did repair SEVERAL wires that were broken or about the break off at the base of their plug (sensor side of harness) and repaired several very weak grounds. prior to this i had a minor 2k rpm hesitation and that is now gone. My ISC valve was also not functioning due to bad wiring. also i got rid of EVERY ECU CEL code :) so i guess it's a good thing that this turned into an involved project, because i've pretty much got a brand new wiring harness now and everything is working as it should. Dave |
yeah, the Service Highlights Manual says the consequence for no knock sensor is "ign timing retarded," which i assumed was just a retard in base timing, not a huge retard at 6-7000rpms.
nevertheless, it was the knock sensor. actually, a slightly update: i hammered through the gears a few times and the knock sensor seems to have just died on me. I am wondering if there is any way to remove the knock sensor and trick the ECU into thinking it's there (like with the emissions solenoids/resistors) |
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