Subalashi

Hi all,
I hope someone will be able to help me, I own an european 2004 Honda S200 with F20C, the setup of the car is the following . stock engine, AEM Infinity ECU with wideband/fuel pressure sensor, test pipe.

The issue occurs at high rpm (from around 6500 rpm), engine has less power, the increase in engine speed is difficult with misfires and hesitations.
I have tried new plugs and new coils, no change, issue is still present. I know think to injectors, MAP sensor and fuel pump, how can i check each of these components to know if one is failing?

Last year, car was running fine, I put it in winter storage and the first drive this year generated the issue described above at high rpm. Nothing has been done or changed to the car except that I cleaned all grounding points as I had starting issue with AEM Infinity. Now that the grounding points are clean, the car is starting fine. Does this grounding points cleaning could have any impact on my high rpm issue? What do you think?

Here is the AEM log where we can see what is happening :

Yellow = throttle
Red = rpm
blue = MAP manifold air pressure

We can see the misfires/hesitations in red, at the same time, manifold air pressure drops massively, what do you think?
Could this be the MAP sensor be failing at high rpm? How can I know if this manifold air pressure drop is the source of the issue or the consequence? How can I test the sensor?

My fuel pressure is always around 50 PSI but sometimes it drops to 45-47 PSI, could this generate any problem?

Thanks a lot for your time and help.

windhund116

So the car ran fine with the AEM Infinity, except for the grounding issues?

Thanks!

Subalashi

Yes that’s it, car ran perfectly fine with the AEM Infinity.

SilentWrath*

Your AFR is going crazy more than the changes in map signal should suggest. I'd have the injectors cleaned/serviced somewhere that can show you flow rate before and after (RC, injector rehab, many others...) If injectors were good I'd probably look towards the pump.

What does your ignition timing do, are you logging that as well? What about injector pulse width?

Is it always the exact same rpm where it begins or does it fluctuate depending on gear?

Slowcrash_101

Yeah you're running super lean up top.

Subalashi

Good point, you are right, my AFR is going crazy comparing to the map signal, I will start with injectors cleaned/serviced, after 20 years it's probably the good moment.

Here is a graph with SparkTiming in orange (corresponding to the previous graph), are you talking about this? I have no knowledge about it, do you see something strange?


And one with Injector pulse :


Does it help?

Comparing the different graphs I have, I would answer No, it's not the exact same rmp where it begins.

Thank your for your help, very appreciated!

SilentWrath*

Hey Subalashi, after taking a closer look I think I was wrong when I jumped to the conclusion that the map signal variation wasn't significant enough to lead to the drastically lean AF conditions you were exhibiting.

I didn't pay attention to the scaling and it seems that fluctuating down to -6.4psi is definitely significant. Idle is around -10.6psi, WOT should be 0.1-0.4. -6.4 is low-mid load cruising.

Anyways, with that said I think it could be a MAP sensor issue. Do you have a buddy with a well running car to swap over and test?

Since the pulse width is decreasing I doubt it is a injector issue. One thing that is extremely strange is that the map fluctuations are not causing changes in the ignition timing. I'm not sure how your calibration of ignition timing is, but when MAP drops to -6.4 your ignition timing should be advancing.

Are you running the OEM intake setup?


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Subalashi

Yes, this was my first idea, MAP drop is important (-6.4), perhaps I should do both, clean injectors + change MAP sensor. Do you think that cleaning the grounding points could have an impact on the MAP sensor (as voltage is not the same)?
Unfortunately, I have no logs when car was running fine to compare. Another element I didn't mention is that I put the OEM ECU to test and result was exactly the same, issue was still present.

Except MAP sensor and injectors, do you see any other element of the car that could generate this issue?

I'm running the OEM airbox with K&N filter and "air box mod" (I cut the "wall" inside the airbox).

Another "problem" I have is that this is a track car only and I'm not authorized to drive it on the street, so it's a little bit annoying to do some tests (need a trailer and a 3 hours drive to go to the track).

Thank you

SilentWrath*

Cleaning ground should only improve them. Are all factory ground points still utilized or were any moves?

To check ground you can look for voltage drop at various points on the chassis with a multimeter. Hold red multimeter probe to battery positive and check voltage with the black probe at the negative battery post. Make note of this reading (likely mid 12v depending on how long car has been sitting). Now move the black probe to various points on the engine, chassis and subframe. With a well grounded setup you should be seeing the same voltage as the one you noted earlier.

There was a Honda service bulletin a long time ago about faulty map sensors. Some users reported "whacking" the map sensor helped...read this thread and the linked threads within:

https://www.s2ki.com/forums/s2000-un...-549145/page2/

If the map is not faulty then to have that much fluctuation in manifold pressure you would need an intermittent blockage of some sort in the intake path. You can remove intake arm and filter to inspect. Open throttle plate and inspect plate condition/operation and inside of intake manifold plenum.

Subalashi

Thank you for you help and advices, very nice from you!