Lean Misfires at 2700-2800 rpm

[DoctorDex]

Originally Posted by venik

try lowering your gap, 40 thousanths is extremely high, i was getting spark blowout at .036 with almost no load, with dr650s i'd say 28-30 thousanths

How old are you coils and what AFR are you tuning to? Are you using copper/platinum/iridium plugs? The only time I ever saw spark blow out using new coils was when I was running pig rich and seeing WOT AFRs of 8-9 (NB:0.99V)

Declan

[DoctorDex]

Originally Posted by venik

try lowering your gap, 40 thousanths is extremely high, i was getting spark blowout at .036 with almost no load, with dr650s i'd say 28-30 thousanths

Thanks for the suggestion, but I already tried narrowing my gap down to 0.28 (with iridiums) and all it did was give me a bit rougher idle and the misfires in 2600-3200 rpm range continued.

How old are you coils and what AFR are you tuning to? What brand of plugs are yu using and are they copper/platinum/iridium plugs? The only time I ever saw spark blow out, using new coils, was when I was running pig rich and seeing WOT AFRs of 8-9 (NB:0.99V) Plus, if it was blow out, it should get worse as boost increases. This problem seems to get better as boost increases, althought I doubt its directly related.



Declan

[DoctorDex]

One idea to get to the bottom of this, would be to create some kind of spreadsheet comparing, side by side, what has been done to our cars, what rpm range they misfire at, what they have in common, ie. year, make, model, ECU part number, ems/fuel management, wires, coils etc. This might give us some clues as to what the possible source/cause is. Does anybody else think this may be of some value?

Does anybody have this problem own a 2nd gen car? A Hybrid ECU? Or are all cases found in 1st gens?

Declan

[venik]

Originally Posted by DoctorDex

Thanks for the suggestion, but I already tried narrowing my gap down to 0.28 (with iridiums) and all it did was give me a bit rougher idle and the misfires in 2600-3200 rpm range continued.

How old are you coils and what AFR are you tuning to? What brand of plugs are yu using and are they copper/platinum/iridium plugs? The only time I ever saw spark blow out, using new coils, was when I was running pig rich and seeing WOT AFRs of 8-9 (NB:0.99V) Plus, if it was blow out, it should get worse as boost increases. This problem seems to get better as boost increases, althought I doubt its directly related.



Declan

not sure if this is directed to me, but i had copper ngks gapped at high 30s my afr was lean at the time, and my coils are factory 1993

[John Monnin]

I tested a known good ECU today and I still have serious lean issue at 3000RPM.

2nd Gear, no boost, at 2800RPM my AF is 13.9 but at 3000RPM it is 16.0, by 4000 RPM it is back to 13.9.

One thing that it might be. I did the vacuum hose reduction because my fuel pressure selenoid seemed to bw working erratically. The fuel pressure selenoid reduces fuel pressure at idle. With it bypassed my car now idles at 13.9 instead of 14.7. I wonder if the ECU is leaning out the fuel too much and when the car is normally getting full fuel pressure the ECU is just not adding enough fuel?

The porblem with this therory is that I had the same problem when I had a fuel controller installed. I was suing the fuel controller to lean mixture out to 14.7 at idle w/o the fuel pressure selinoid.

What we really need is a list of all the passible causes and what to check.

For example:
Possible causes:
1. Bad Ecu: Check by borrowing a good ECU from a friend
2. Spark blowout: Reduce plug gap and see if problem gets better
3. Bad MAF Sensor: Check by borrowing a good MAF sensor from a friend
4. IAT Sensor, Intake air tempuratue sensor, Check Datalog and make sure value is normal, My car's intake tempuratures are usually 30-60 deg hotter that outside tempuratures when idling and only 20-30 deg hotter than outside when cruising (no boost)
5. O2 sensors, check that ALL O2 sensors are cycling normally at idle
6. TPS Switch, Use datalogger to check the TPS switch, it should switch from on to off if you press on the gas pedal at all, and it should switch from off to on when you left off the gas completely
7. TPS adjustment, Datalogger should show between (8 and 14 ???) at idle and it shoudl increase to ??? when gas pedal is fully depressed.
8. Vaccum leaks, Use an intake pressure tester adn eliminate any boost leaks.

Anything Else? Coolant temp sensors? Electical connections, ground wires?????

I probably should re-prioritize the list so that anything that can be checked with a datalogger is checked first.

[DoctorDex]

The fuel pressure solenoid increases fuel pressure during "hot starts" and it doesn't do anything at idle. I believe you have it confused with the fuel pump relay that switches the amount of voltage going to the pump during idle/boost.

[DoctorDex]

John what kind of fuel pump do you have and have you done any rewiring/hotwiring of the pump?

[keithmac]

Just to chime in again, my 1st gen is stock apart from boost control/ K+N induction kit/ Magnecore wires/ blow off valve and single outlet exhaust system.

It was running horrifically before I replaced the caps, runs a thousand times better now BUT I`ve been experiencing the 2800 to 3000 rpm flat spot/ lean out at part throttle and just below 0 psi to approx 3psi on the boost gauge.

I honesetly beleive it`s a quirk in the fuel map on the ECU, or is it possibly the change over from closed to open loop operation?. To be honest it doesn`t really get in the way for me but it would be nice to get it sorted. I`m running a Japanese GTO TT.

[John Monnin]

Originally Posted by DoctorDex

The fuel pressure solenoid increases fuel pressure during "hot starts" and it doesn't do anything at idle. I believe you have it confused with the fuel pump relay that switches the amount of voltage going to the pump during idle/boost.


John what kind of fuel pump do you have and have you done any rewiring/hotwiring of the pump?

I believe you are right, I should never try to work from memory.

I have a relay so tha the fuel pump recieves full voltage all the time. My fuel pressure gauge shows that the fuel pressure is normalwhen this lean situation occurs.

[John Monnin]

Originally Posted by deyer

I think this might be the same problem i'm having right now...

Any help would be greatly appreciated

It misfires between 2,000 - 2,500 RPM. Not horrible misfireing, but it's not very driveable. You can also hear it slightly at idle.

So far the mechanic has tried:

NEW
Spark Plugs
Spark Plug Wires
Coil Pack
Air Flow Meter
Fuel Filter
Drained the gas tank and tried new fuel
Cleaned Fuel Injectors
O2 Sensors
TPS

Also the Cam and Ignition timming are all correct.
The Compression is correct as well.

Everything is stock on the car, not one after market part.

I read about the ECU... if that won't fix it then.....??????

I hope you didn't have to pay for all of that, you are paying a dealer for thier experience and diagnosing skills, Any idiot can just swap parts and hope it works.

If they are just swapping parts and charging you money, they are laughing all the way to the bank, I would demand that they give you your old parts back if your car still runs bad.