light load misfire

[ozi_milhouse]

Thanks G.

The drive this morning was just a cruise to work so 106kpa i would have thought to be normal.

You are right when i said it pulls strong at anything highers than 45 kpa with no missing. It only misses on light throttle.

What would you suggest a normal Map reading at cruise would be? i would have thought 30ish is about right?

With a closed throttle i see it down at around 15. Bare in mind the motor is stock.

Will check for vaccuum leaks. Generally though on the track under partial and full throttle i am rich which is the way i need it for that situation. but at cruise i hover.

MIght try reconnecting the stock narrow band from the computer and read what the AEM reads then.

cheers for the help and suggestions

Justin

[gslender]

What would you suggest a normal Map reading at cruise would be? i would have thought 30ish is about right?

In your log I am seeing closer to 20kPa as being the MAP during cruise conditions (ie steady state TP > 5% with RPM siting in a steady band around 3000).

I would normally see around 40kPa as being the normal for that type of cruise event.

Elsewhere in the log you hit 23% throttle and the MAP jumps to 28kPa... that's not right. It should be at least 60-100 kPa with that much throttle open.

On average, your map value was 28kPa... so extremly low that I'm just skeptical.

Also, I doubt very much that your MAP only ever got higher than 106kPa as during those 100% TP periods the turbo should have been producing some kind of additional air pressure, even if just 2 psi above atmos, that would be at least 112kPa so I'd be surprised if you didn't do better than that, but you are right, it would be techinically possible to not hit a hint of boost, though I'm just surprised that you didn't - at all, ever, anywhere.

G

[jerrah]

As Gslender knows I had a bad MPXH6400 mapdaddy sensor in my Megasquirt. We swapped it to a stock MPX4250AP which resolved my MAP weirdness. My MPXH6400 had an incorrect reading for ambient pressure (engine off) even after calibration.

Do you have a boost gauge? What does your megasquirt log when it's in boost? What reading do you get with the engine off?

[gslender]

As Gslender knows I had a bad MPXH6400 mapdaddy sensor in my Megasquirt. We swapped it to a stock MPX4250AP which resolved my MAP weirdness. My MPXH6400 had an incorrect reading for ambient pressure (engine off) even after calibration.

Do you have a boost gauge? What does your megasquirt log when it's in boost? What reading do you get with the engine off?

Good point!

Confirm your map reading is 101 when ignition on, but engine not running/cranking. If not then your map sensor is bad or calibration is out.

G

[ozi_milhouse]

Yeah that could be it. with ignition on and car not running i read about 66kpa.

in sydney barometric pressure is about 101kpa (as per jerrah's note)

so somethign is wrong there. But it has always read that way and the dyno tuner tuned it and scaled the maps accordingly (as you can see in the msq map only scales to about 138kpa)

so not ideal but looks as though he has tuned and adjusted accordingly.

Also i have an aux boost gauge. i boost to 10psi regularly on the track from about 3500rpm with moderate throttle. I'll have to look into this map sensor and maybe rescale my maps and spend some time on the dyno, or just accept the current scaling and work with that. not ideal but much cheaper. And this really doesnt explain my miss either. I briefly ran hi res firmware last night and the miss was imperceptible. which leads me to believe it could be an injector issue?

thanks for the input guys.

[jerrah]

66kpa with the engine off is very wrong and you can't trust what it's reading.

Either you're out of calibration or it's broken. It's why the readings don't make sense in your log file.

Have you tried recalibrating it? What sensor model are you calibrating it for in Tunerstudio?

[gslender]

I briefly ran hi res firmware last night and the miss was imperceptible. which leads me to believe it could be an injector issue?

I hate troubleshooting problems when something else is wrong.

The tune doesn't look like its scaled correct for 66kpa and it is running lean almost everywhere except wot.

Fix the map sensor or at least see what its like when it is working correctly.

We couldn't get jarrahs to tune and run right until we fixed the map sensor. As soon as we did it ran beaut!

G

[ozi_milhouse]

So the guy i bought the car off installed the megasquirt. he also bought the 4 bar map sensor. but when it was tuned it wasn't configured correctly and was set up in tune as if it was running the 2.5bar map sensor that is standard. hence the low kpa values. i changed the configuration to the 4 bar unit. Low and behold steady 100kpa at ignition on but car not running.

SO i was right with my assumption about the wrong map configuration thanks to your input on the low kpa's. Only problem is that the ve tables were now all wrong. DId a basic scale change of multiplying the existing kpa scales by 1.6 to get close to the existing tune.

At the same time i uploaded hires firmware. Here is where the issue is. started running auto tune to get the tune right and hoped to see if the new firmware fixed the miss at about 3000. but it didnt which meant at around the 3000 mark is rubbish. I then manually flooded the 4 cells around the problem area. if i ran the engine at 3000 rpm with about 11 afr or richer then the miss just about dissapears.

would that point towards an injector issue do you think? im running 550cc high impedance rx7 injectors.

[gslender]

How certain are you that the o2 sensor is correct? At 11afr it should be stumbling again... Too rich. If you're saying it's running ok, then maybe it's also reporting incorrectly. When was the last free air calibration?

G

[NitroDann]

The guage is wrong and the car is too lean.

So back to my original post.

Configure everything properly and tune it.

Dann

[ozi_milhouse]

Hey Guys,

Thanks for your interest. Its a NEW AEM 02 Gauge, no free calibration needed. I don't believe its running lean at all, it only reads lean at around the 3000 mark when the miss occurs and an occassional spike when accelerating because i had AE switched off to allow me to try and figure out this miss.

I exagerated on the AFR. When i richened it up it was closer to 11.5afr at the 3000 range it was only at very light load (i.e. free reving) that saw the miss disappear. Driving it around like this was a complete dog.

Im in a catch 22. I can't tune around the miss because it gives a terrible tune due to the lean spike recorded from the miss. Once i fix the miss i can retune.

I'm going to try new leads again (the ones i have on it are new magnecros) and buy some cheap oem ones and see if that works on the chance that the magnecors are bad from factory. Also will change plugs for some cooler ones and see how i go. This is really getting me down...... Thanks for your help so far. Will try the new leads and plugs and report back. Doubt it is this but its a cheap enough sanity check.

[NitroDann]

theres no such thing as no calibration

Calibrate it or use a different WB02

Dann

[ozi_milhouse]

Hey Dann,

Link to AEM website below. Calibrated at factory and doesn't require any other calibration.

http://www.aemelectronics.com/wideband- ... -gauge-25/

Cheers

Justin

[manga_blue]

Seen this? http://forum.aempower.com/forum/index.php?topic=27324.0

[ozi_milhouse]

cheers,

well theres no variation between the gauge reading and the megasquirt reading so that's a bonus. But i will need to check it with another sensor. Maybe need to head back to the dyno.............. more dollars gone....

Justin