1990 S5 N/A hesitation near 7500rpms
#1
REINCARNATED
Thread Starter
iTrader: (4)
1990 S5 N/A hesitation near 7500rpms
Stock ports, stock intake, stock ECU full RB true duals header back to RB mufflers. Running 87 octane and 1oz of idemitsu per gallon of fuel. no OMP
The other day I encountered something strange while on my way back home. The car seemed to stumble just a bit around the 7500rpm mark. I immediately let off throttle and attempted to replicate the issue which did occur again around the same RPM. This was in 2nd gear.
Any thoughts or idea's? Engine has approx 72000 miles.
Thanks, -M
The other day I encountered something strange while on my way back home. The car seemed to stumble just a bit around the 7500rpm mark. I immediately let off throttle and attempted to replicate the issue which did occur again around the same RPM. This was in 2nd gear.
Any thoughts or idea's? Engine has approx 72000 miles.
Thanks, -M
#3
Rotorhead for life
iTrader: (4)
If the car runs smooth & fine otherwise under load and varied RPMs, my first guess would be the ignition system is breaking down at high RPMs where it would be stressed the most. Try a fresh set of spark plugs & plug wires first and see if that improves things.
One other thing to add - I'm pretty sure the stock FC ECU has a rev limiter feature that cuts fuel/spark when the limit is reached. Shouldn't happen until 8K RPMs or so, but perhaps your tach is inaccurate (reading low), and you were just hitting the rev limit when it stumbled?
One other thing to add - I'm pretty sure the stock FC ECU has a rev limiter feature that cuts fuel/spark when the limit is reached. Shouldn't happen until 8K RPMs or so, but perhaps your tach is inaccurate (reading low), and you were just hitting the rev limit when it stumbled?
Last edited by Pete_89T2; 04-05-18 at 11:50 AM. Reason: Added info.
#5
REINCARNATED
Thread Starter
iTrader: (4)
The plugs are new with approx 100 miles on them. I did not change the wires however and NEED to. I have only ever heard the coolant buzzer and it's associated light when installing a new radiator. I have never heard the shift buzzer like I did when I owned an 86 GXL.
Is the coolant / Oil buzzer the same buzzer for shifting? Thank you,
-M
Is the coolant / Oil buzzer the same buzzer for shifting? Thank you,
-M
#6
REINCARNATED
Thread Starter
iTrader: (4)
If the car runs smooth & fine otherwise under load and varied RPMs, my first guess would be the ignition system is breaking down at high RPMs where it would be stressed the most. Try a fresh set of spark plugs & plug wires first and see if that improves things.
One other thing to add - I'm pretty sure the stock FC ECU has a rev limiter feature that cuts fuel/spark when the limit is reached. Shouldn't happen until 8K RPMs or so, but perhaps your tach is inaccurate (reading low), and you were just hitting the rev limit when it stumbled?
One other thing to add - I'm pretty sure the stock FC ECU has a rev limiter feature that cuts fuel/spark when the limit is reached. Shouldn't happen until 8K RPMs or so, but perhaps your tach is inaccurate (reading low), and you were just hitting the rev limit when it stumbled?
Trending Topics
#8
REINCARNATED
Thread Starter
iTrader: (4)
The physical gauge shows 8k as the beginning of the redline. I am unsure what the ECU programming will allow before cut. I'd have to agree, there is probably not much more power up at that RPM.
#9
Information Regurgitator
8k. On mine the buzzer goes off at 8k and the rev limiter kicks in at 8500rpm. Maybe the OP's buzzer is disabled like he suspects. When I had a stock port power noticeably fell off around 7500. To the point of not really being any reason to rev any higher. I had the RB collected header pre silencer system with HKS sport cat back at the time.
The following users liked this post:
Relisys190 (04-05-18)
The following users liked this post:
Relisys190 (04-05-18)
The following users liked this post:
Relisys190 (04-06-18)
#14
Moderator
iTrader: (3)
Join Date: Mar 2001
Location: https://www2.mazda.com/en/100th/
Posts: 30,780
Received 2,564 Likes
on
1,824 Posts
The plugs are new with approx 100 miles on them. I did not change the wires however and NEED to. I have only ever heard the coolant buzzer and it's associated light when installing a new radiator. I have never heard the shift buzzer like I did when I owned an 86 GXL.
Is the coolant / Oil buzzer the same buzzer for shifting? Thank you,
-M
Is the coolant / Oil buzzer the same buzzer for shifting? Thank you,
-M
if you haven't checked the wires yet, these are good candidates. new they will be in the 7k Ohm range, and the upper limit is 16k Ohms. the higher the resistance the less spark energy you have, so at 16k Ohms if it isn't misfiring at high rpm, its about to.
another place to look is to check for codes, i've seen TPS codes only come on at WOT, and it will cause a hesitation/cut, CEL may or may not do anything
it is NLA from Mazda, use Denso number 952-0043 please
#15
REINCARNATED
Thread Starter
iTrader: (4)
the buzzers are different.
if you haven't checked the wires yet, these are good candidates. new they will be in the 7k Ohm range, and the upper limit is 16k Ohms. the higher the resistance the less spark energy you have, so at 16k Ohms if it isn't misfiring at high rpm, its about to.
another place to look is to check for codes, i've seen TPS codes only come on at WOT, and it will cause a hesitation/cut, CEL may or may not do anything
it is NLA from Mazda, use Denso number 952-0043 please
if you haven't checked the wires yet, these are good candidates. new they will be in the 7k Ohm range, and the upper limit is 16k Ohms. the higher the resistance the less spark energy you have, so at 16k Ohms if it isn't misfiring at high rpm, its about to.
another place to look is to check for codes, i've seen TPS codes only come on at WOT, and it will cause a hesitation/cut, CEL may or may not do anything
it is NLA from Mazda, use Denso number 952-0043 please
Thanks very much for the information!
#17
Rotary Freak
iTrader: (1)
My 91 NA reliably revs to 8700 with no fuel cut (it does run out of breath and stop accelerating at that point on stock ports however). My understanding is the factory ECU cuts fuel at 9000, which I can't speak to, since I can't get there. My shift warning buzzer sounds at about 78-7900rpm, which I understand is about right, it's supposed to sound before you hit the theoretical redline, since it's easy to blow past.
Besides the plugs and wires, check the engine grounds, since poor grounds can also cause weak spark/ignition breakup.
Besides the plugs and wires, check the engine grounds, since poor grounds can also cause weak spark/ignition breakup.
Thread
Thread Starter
Forum
Replies
Last Post
FC3S Timmy
2nd Generation Specific (1986-1992)
3
06-21-09 10:31 AM
my87rx
2nd Generation Specific (1986-1992)
2
09-06-08 01:18 PM
seventhgear
2nd Generation Specific (1986-1992)
7
01-12-03 07:24 AM