hitting fuel cut at 10psi
#26
Racecar - Formula 2000
Dave
#27
Warming the planet.
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
Paul
#28
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
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
#31
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!
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!
#34
Original Owner
iTrader: (1)
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.
Last edited by Retserof; 11-29-08 at 10:49 PM.
#35
always modding
Join Date: Mar 2005
Location: on a tiny island in the middle of a sea
Posts: 1,667
Likes: 0
Received 3 Likes
on
3 Posts
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
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
#36
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
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...
#37
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.
#38
~17 MPG
iTrader: (2)
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.
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.
#39
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.
i put resistors in all the emissions solenoids and hooked the knock sensor up and i have no CELs and the car runs perfectly.
#40
Project Restore
iTrader: (6)
Join Date: Jan 2004
Location: Houston
Posts: 219
Likes: 0
Received 0 Likes
on
0 Posts
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?
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?
#42
Senior Member
iTrader: (20)
Join Date: Mar 2008
Location: LosT Angeles
Posts: 416
Likes: 0
Received 0 Likes
on
0 Posts
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).
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).
#44
Project Restore
iTrader: (6)
Join Date: Jan 2004
Location: Houston
Posts: 219
Likes: 0
Received 0 Likes
on
0 Posts
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...
#46
Racecar - Formula 2000
#47
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.
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.
Last edited by jacobcartmill; 12-09-08 at 05:28 PM.
#48
Racecar - Formula 2000
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.
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
#49
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)
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)
Thread
Thread Starter
Forum
Replies
Last Post
Snook
3rd Generation Specific (1993-2002)
21
09-01-15 06:32 PM
armans
3rd Generation Specific (1993-2002)
5
08-15-15 09:08 PM