Cant stop the Fuel Cut in 1998 Sr20det~!! HELP - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

SRfairladyZ · 06-21-2005, 08:25 PM

I have a 98 Sr20det engine and I'm having a problem at high rpm (under load), its at about 5600rpm i get a fuel cut (even at stock boost!!), happend on the dyno, watched my a/f reading rocket to 20 when the cut happends so i know its fuel or ignition being totaly haulted. I'm running the Q45 maf, i tried putting my stock maf in and it did the same thing. Also running a SAFC2, bypassed it, still cut. I cant seem to find the problem. Could not having my speed sensor hooked up cause this fuel cut? Btw this engine is in a 71 240Z using the SR20 engine harness and ECU, painless wiring for the ignition power, fuel pump and ECU power. I tried using a HKS fuel cut defenser, it did stop the fuel cut for the most part but, made me run dangerously lean, and made my SAFC2 go haywire, so i took it off. Please help...
getting frustrated.

Blues13 · 06-21-2005, 10:26 PM

Did you try checking the spark plug gap? Try reducing the gap as too large of a gap tends to have the plug blow out. SRs are really finicky about that. Let's see some pics of the car!

monkeyspeed · 06-22-2005, 07:21 AM

also, check your fuel pump and sock. have you checked the fuel pressure?

g2ic02 · 06-22-2005, 07:37 AM

what are you using for a fuel filter???

SRfairladyZ · 06-22-2005, 12:51 PM

Hey, spark plug gaps can cause fuel cuts??? I know plug gaps can easly cause breakups and missfires. but fuel cuts aswell?

My fuel system (besides my stock injectors) can support around 500whp. Its a huge and loud SX engineering fuel pump and filter, 10gal fuel cell with -6 lines from the tank to the rail, and an SX fuel pressure regulator that hits around 3.5bar at boost. So fuel starvation isnt my problem. Can a bad injector cause a full ignition cut? Please keep the ideas coming! Tried to hook up the speed sensor to the ECU but cant seem to figure out how it works, theres 2 pins on the speed sensor and 1 ECU wire, the wiring diagrams dont make much sense either, which pisses me off. I think maybe since the speed sensor isnt hook up, the ECU is cutting me off becuase it cannot read the signal for speed cut? Heres the ride...

Thanks for your help and ideas people.

Blues13 · 06-22-2005, 01:28 PM

Awesome ride! Really diggin the flares. That SR looks TINY in that engine bay.. hahaha.

If it's a total fuel cut and you can't rev past 5600rpm even real slowly, then it's probably not the spark plugs. Too large a gap on the plugs will feel like a fuel cut under load, but if you let off the throttle you should still be able to rev slowly up until redline.

I'm not positive, but it sounds like it is your speed sensor/ecu.. it doesn't know how fast you're going so it's cutting it at 5600rpm. I eliminated my speed limiter by cutting the green/yellow(I think??) wire going to the ecu.. I don't know if that will help?

SRfairladyZ · 06-22-2005, 02:43 PM

Blues13 you have a S14 Sr20?
Yep the Green/Yellow wire is pin 32 the signal wire for the speed sensor. Yours is cut, therefor your ECU isnt seeing the speed signal, BUT your not getting fuel cuts due to it being cut, So that answer my question. Its not speed sensor being disconnected thats my problem...unless its diffrent for an S14? hm, reving up slowly to redline sounds like a good test to try, In 1st gear which is all wheels spin, i can fly upto 7500rpm w/o a cut, but in 2nd when i'm getting gobs of tourqe and traction it cuts quickly. 3rd gear will cut aswell, never tried 4th or 5th.

Thanks for the compliments, they allways help in these times of frustration.

g2ic02 · 06-22-2005, 04:00 PM

Are you 100% sure you don't have a boost leak??? I know my scenario is a tad bit different, but i will explain it anyways. When i boosted to 14psi in first/second gear it would be fine, but then when i was in a gear where my felt a larger load(sometimes 3rd, but 4th and 5th for sure) it would cut. I got t-bolt clamps for all my intercooler piping and gapped my plugs and the problem went away. Hopefully you figure out your problem. Your project is awesome.

g2ic02 · 06-22-2005, 04:01 PM

sorry disreguard that whole last post....forgot that you experienced lean conditions.

g2ic02 · 06-22-2005, 04:07 PM

wouldn't a bad spark plug gap show up as a rich a/f ratio? I would say the next thing to try is your injectors.

SRfairladyZ · 06-22-2005, 04:27 PM

Yep, thats the diffrence between fuel cut and missfire, the air / fuel reading on a missfire would be rich from the unburt fuel that the plug is missing.
In a Fuel cut you will see the air / fuel reading jump all the way lean, cause there is NO fuel for that 1 second cut. This is not a gapping problem or missfiring problem. Leaking IC piping results in missfires if i remember correctly, not fuel cuts. Dropped a note on www.mckinneymotorsports.com hopfully they can pull through for me. but still, please keep idea's coming...
Thanks!

97DubTruck · 06-22-2005, 09:02 PM

God your car is the hot sauce. Sounds like its just breaking up really bad. Go get another tune. McKinney did my old harness and it worked fine, they do pretty good work.

sepulchral · 06-22-2005, 10:40 PM

i had same prob, make sure your fuel filter is not clogged with rusty 240z gas tank shit... have you checked ecu for error codes?

SRfairladyZ · 06-22-2005, 11:05 PM

Shit, wish i could check codes, i dont have the dash harness, and its odb2 with no light in the ECU, so i'm blind basicly. Theres deffenatly no old 240Z gas in this tank...

MACK from McKinney said check codes, sounds like my fuel pump is the prob but its not, since my fuel pressure doesnt drop at all when the cut hits. Also said MAF, but i triend 3 diffrent ones, maybe i'll go for four, I'll try a Z32 one. this is getting rough, damn. Thanks again guys.

SRfairladyZ · 07-09-2005, 10:44 PM

Finaly, the 3rd MAFS worked. Belive that? i went though 3 sensors? First was a Q45 one, Then another Q one, then i figured maybe it was the Q model sensor that was the prob, so someone let me barrow a so called S14 MAF but i believe it was a S13 one since my car ran like balls with it on. So today i tired a Z32 one and the bitch pulled all the way to 7500 like a champ. At 1bar the car is a complete animal. So i dont recomend the Q maf on an S14, nor anything elts at that since it does not give high enough voltages to support over 250whp. God damn it, i knew it was the MAFS. good thing i was subburn about it. Thanks for anyone looking. - hope this helps some one out there who had it like me.

06-21-2005, 08:25 PM	#1
SRfairladyZ Leaky Injector Join Date: Feb 2005 Location: nyc Posts: 56 Trader Rating: (0) Feedback Score: 0 reviews	Cant stop the Fuel Cut in 1998 Sr20det~!! HELP I have a 98 Sr20det engine and I'm having a problem at high rpm (under load), its at about 5600rpm i get a fuel cut (even at stock boost!!), happend on the dyno, watched my a/f reading rocket to 20 when the cut happends so i know its fuel or ignition being totaly haulted. I'm running the Q45 maf, i tried putting my stock maf in and it did the same thing. Also running a SAFC2, bypassed it, still cut. I cant seem to find the problem. Could not having my speed sensor hooked up cause this fuel cut? Btw this engine is in a 71 240Z using the SR20 engine harness and ECU, painless wiring for the ignition power, fuel pump and ECU power. I tried using a HKS fuel cut defenser, it did stop the fuel cut for the most part but, made me run dangerously lean, and made my SAFC2 go haywire, so i took it off. Please help... getting frustrated.

06-21-2005, 10:26 PM	#2
Blues13 Zilvia Junkie Join Date: Jul 2003 Location: OC Posts: 435 Trader Rating: (2) Feedback Score: 2 reviews	Did you try checking the spark plug gap? Try reducing the gap as too large of a gap tends to have the plug blow out. SRs are really finicky about that. Let's see some pics of the car!

06-22-2005, 07:21 AM	#3
monkeyspeed Leaky Injector Join Date: Apr 2004 Location: jax, fl Posts: 62 Trader Rating: (0) Feedback Score: 0 reviews	also, check your fuel pump and sock. have you checked the fuel pressure?

06-22-2005, 07:37 AM	#4
g2ic02 Zilvia Junkie Join Date: Jul 2003 Location: minnesota Posts: 480 Trader Rating: (3) Feedback Score: 3 reviews	what are you using for a fuel filter???

06-22-2005, 12:51 PM	#5
SRfairladyZ Leaky Injector Join Date: Feb 2005 Location: nyc Posts: 56 Trader Rating: (0) Feedback Score: 0 reviews	Hey, spark plug gaps can cause fuel cuts??? I know plug gaps can easly cause breakups and missfires. but fuel cuts aswell? My fuel system (besides my stock injectors) can support around 500whp. Its a huge and loud SX engineering fuel pump and filter, 10gal fuel cell with -6 lines from the tank to the rail, and an SX fuel pressure regulator that hits around 3.5bar at boost. So fuel starvation isnt my problem. Can a bad injector cause a full ignition cut? Please keep the ideas coming! Tried to hook up the speed sensor to the ECU but cant seem to figure out how it works, theres 2 pins on the speed sensor and 1 ECU wire, the wiring diagrams dont make much sense either, which pisses me off. I think maybe since the speed sensor isnt hook up, the ECU is cutting me off becuase it cannot read the signal for speed cut? Heres the ride... Thanks for your help and ideas people.

06-22-2005, 01:28 PM	#6
Blues13 Zilvia Junkie Join Date: Jul 2003 Location: OC Posts: 435 Trader Rating: (2) Feedback Score: 2 reviews	Awesome ride! Really diggin the flares. That SR looks TINY in that engine bay.. hahaha. If it's a total fuel cut and you can't rev past 5600rpm even real slowly, then it's probably not the spark plugs. Too large a gap on the plugs will feel like a fuel cut under load, but if you let off the throttle you should still be able to rev slowly up until redline. I'm not positive, but it sounds like it is your speed sensor/ecu.. it doesn't know how fast you're going so it's cutting it at 5600rpm. I eliminated my speed limiter by cutting the green/yellow(I think??) wire going to the ecu.. I don't know if that will help?

06-22-2005, 02:43 PM	#7
SRfairladyZ Leaky Injector Join Date: Feb 2005 Location: nyc Posts: 56 Trader Rating: (0) Feedback Score: 0 reviews	Blues13 you have a S14 Sr20? Yep the Green/Yellow wire is pin 32 the signal wire for the speed sensor. Yours is cut, therefor your ECU isnt seeing the speed signal, BUT your not getting fuel cuts due to it being cut, So that answer my question. Its not speed sensor being disconnected thats my problem...unless its diffrent for an S14? hm, reving up slowly to redline sounds like a good test to try, In 1st gear which is all wheels spin, i can fly upto 7500rpm w/o a cut, but in 2nd when i'm getting gobs of tourqe and traction it cuts quickly. 3rd gear will cut aswell, never tried 4th or 5th. Thanks for the compliments, they allways help in these times of frustration.

06-22-2005, 04:00 PM	#8
g2ic02 Zilvia Junkie Join Date: Jul 2003 Location: minnesota Posts: 480 Trader Rating: (3) Feedback Score: 3 reviews	Are you 100% sure you don't have a boost leak??? I know my scenario is a tad bit different, but i will explain it anyways. When i boosted to 14psi in first/second gear it would be fine, but then when i was in a gear where my felt a larger load(sometimes 3rd, but 4th and 5th for sure) it would cut. I got t-bolt clamps for all my intercooler piping and gapped my plugs and the problem went away. Hopefully you figure out your problem. Your project is awesome.

06-22-2005, 04:01 PM	#9
g2ic02 Zilvia Junkie Join Date: Jul 2003 Location: minnesota Posts: 480 Trader Rating: (3) Feedback Score: 3 reviews	sorry disreguard that whole last post....forgot that you experienced lean conditions.

06-22-2005, 04:07 PM	#10
g2ic02 Zilvia Junkie Join Date: Jul 2003 Location: minnesota Posts: 480 Trader Rating: (3) Feedback Score: 3 reviews	wouldn't a bad spark plug gap show up as a rich a/f ratio? I would say the next thing to try is your injectors.

06-22-2005, 04:27 PM	#11
SRfairladyZ Leaky Injector Join Date: Feb 2005 Location: nyc Posts: 56 Trader Rating: (0) Feedback Score: 0 reviews	Yep, thats the diffrence between fuel cut and missfire, the air / fuel reading on a missfire would be rich from the unburt fuel that the plug is missing. In a Fuel cut you will see the air / fuel reading jump all the way lean, cause there is NO fuel for that 1 second cut. This is not a gapping problem or missfiring problem. Leaking IC piping results in missfires if i remember correctly, not fuel cuts. Dropped a note on www.mckinneymotorsports.com hopfully they can pull through for me. but still, please keep idea's coming... Thanks!

06-22-2005, 09:02 PM	#12
97DubTruck Zilvia Junkie Join Date: Sep 2003 Location: location, location Posts: 532 Trader Rating: (0) Feedback Score: 0 reviews	God your car is the hot sauce. Sounds like its just breaking up really bad. Go get another tune. McKinney did my old harness and it worked fine, they do pretty good work.

06-22-2005, 10:40 PM	#13
sepulchral BANNED Join Date: Mar 2004 Location: Midlothian. VA Posts: 2,050 Trader Rating: (0) Feedback Score: 0 reviews	i had same prob, make sure your fuel filter is not clogged with rusty 240z gas tank shit... have you checked ecu for error codes?

06-22-2005, 11:05 PM	#14
SRfairladyZ Leaky Injector Join Date: Feb 2005 Location: nyc Posts: 56 Trader Rating: (0) Feedback Score: 0 reviews	Shit, wish i could check codes, i dont have the dash harness, and its odb2 with no light in the ECU, so i'm blind basicly. Theres deffenatly no old 240Z gas in this tank... MACK from McKinney said check codes, sounds like my fuel pump is the prob but its not, since my fuel pressure doesnt drop at all when the cut hits. Also said MAF, but i triend 3 diffrent ones, maybe i'll go for four, I'll try a Z32 one. this is getting rough, damn. Thanks again guys.

07-09-2005, 10:44 PM	#15
SRfairladyZ Leaky Injector Join Date: Feb 2005 Location: nyc Posts: 56 Trader Rating: (0) Feedback Score: 0 reviews	Finaly, the 3rd MAFS worked. Belive that? i went though 3 sensors? First was a Q45 one, Then another Q one, then i figured maybe it was the Q model sensor that was the prob, so someone let me barrow a so called S14 MAF but i believe it was a S13 one since my car ran like balls with it on. So today i tired a Z32 one and the bitch pulled all the way to 7500 like a champ. At 1bar the car is a complete animal. So i dont recomend the Q maf on an S14, nor anything elts at that since it does not give high enough voltages to support over 250whp. God damn it, i knew it was the MAFS. good thing i was subburn about it. Thanks for anyone looking. - hope this helps some one out there who had it like me.