AFR problems

Chilliman · Post by **Chilliman** » Tue Apr 17, 2012 9:51 am

Hi all, engine is RV8 5 litre (TVR Chimaera), V8Dev build and includes bespoke cam, ACT triple throttle bodies, Megasquirt fuel & ignition running coil packs and high flow injectors. Graph below was just after running in, couldn't dial out the rich running with a map, suspect not enough air getting to the TB's so looking at filter (in the nose) and hose up to the ACT CF airbox. RR gave 355bhp at the fly and 335 torques, but power curve starts to 'flatten' (or rather its not as steep) at around 4500rpm. Peak power was at 6250, but as you can see she really goes rich from about 5600rpm. AFR at peak power has dropped to less than 12

Does anyone have an AFR graph for an RV8 showing a typical 'optimum' AFR curve? Any thoughts on the graph welcome.... Hoping to iron this problem out, I'm convinced there's a few more horses yet to come

Three failed attempts to get the graph up.... HELP!!!

SuperV8 · Post by **SuperV8** » Tue Apr 17, 2012 12:15 pm

You need to have the photo/image saved with an online image host, I use Photobucket.
Then just copy and paste the IMG code link into the post.

couldn't dial out the rich running with a map

Sounds strange, the idea is you you can dial in what ever AFR is needed. Should be straight forward to take some fuel out where it's running rich.

Tom.

ChrisJC · Post by **ChrisJC** » Tue Apr 17, 2012 12:22 pm

HTH,

Chris.

Ian Anderson · Post by **Ian Anderson** » Tue Apr 17, 2012 12:36 pm

Have you got a Rising rate fuel pressure regulator?

If so has the rising pressure generated been worked into the fuel map?

If not higher pressure = higher flow which could account for this richening

Ian

DaveEFI · Post by **DaveEFI** » Tue Apr 17, 2012 12:37 pm

Can you post your MS AFR and VE tables?

Chilliman · Post by **Chilliman** » Tue Apr 17, 2012 4:19 pm

Hi guys, thanks for the replies..

I don't have a rising rate fuel pressure regulator... Unable also to post the AFR and VE tables as the last map was done at the engine builders. Going to fit new filter(s) and hose up to the air box that houses the TB trumpets then get her back on the RR for some diagnostics. Some of the guys on PH have posted their AFR graphs and are maintaining a good 12.5 to 12.8 from around 4k upwards, although they're still running the 14CUX system (One has a Mark Adams best guess chip). I have yet to understand the mapping process and the soft ware well enough to do it myself although I'm sure I'll leave it to the experts. Thanks for the input guys, I'll get a print out when she's next mapped and post it up.

And thanks ChrisJC for getting my graph up

SuperV8, thanks, suspicion at the moment is that its not enough air rather than too much fuel, so we could reduce the fuelling to meet the air available (I think) but then we wouldn't be getting the maximum achievable power (feel free to correct me if I'm talking tosh

)

Chilli.

SuperV8 · Post by **SuperV8** » Tue Apr 17, 2012 5:50 pm

Chilli,

suspicion at the moment is that its not enough air rather than too much fuel, so we could reduce the fuelling to meet the air available (I think) but then we wouldn't be getting the maximum achievable power (feel free to correct me if I'm talking tosh )

A restriction in air could well reduce potential power but it would not lead to runnig rich. Megasquirt will calculate the air mass and then add fuel depending on the value in the VE table. If the air filter or piping is restricting air flow, the megasquirt won't know this, it will fuel for the air flow the engine is actually getting.

Could it be that the engine tunner has made it rich as a precaution? Rich is safer than too lean at high loads and rpm.

Tom.

Chilliman · Post by **Chilliman** » Tue Apr 17, 2012 7:07 pm

SuperV8 wrote:Chilli,

suspicion at the moment is that its not enough air rather than too much fuel, so we could reduce the fuelling to meet the air available (I think) but then we wouldn't be getting the maximum achievable power (feel free to correct me if I'm talking tosh )
A restriction in air could well reduce potential power but it would not lead to runnig rich. Megasquirt will calculate the air mass and then add fuel depending on the value in the VE table. If the air filter or piping is restricting air flow, the megasquirt won't know this, it will fuel for the air flow the engine is actually getting.

Could it be that the engine tunner has made it rich as a precaution? Rich is safer than too lean at high loads and rpm.

Tom.

Hi Tom, yes actually that's a distinct possibility, and what you say makes perfect sense. The RR session that produced the AFR graph was shortly after I'd finished running the new engine in, so it makes sense that it would be a 'safe' map... I'll go ahead with the smooth bore inlet hose as these are a known weak point on the standard cars (TVR cost cutting

), check out the filter (I'm working away at the moment) and go for a RR remap. I'm fortunate enough to be in touch with Phil at extraEFI as I don't live too far from him (near Norwich) so I'm hoping to enlist his help as he uses the same RR as I do.... Many thanks again, Richard.

DaveEFI · Post by **DaveEFI** » Tue Apr 17, 2012 9:55 pm

The MS map is in it - so all you have to do is connect your laptop to it and Tuner Studio will capture it. You should do this as a matter of course anyway - just in case of the unlikely event of an MS 'crash'.

It's impractical to get MS set up totally and perfectly on a rolling road for all speeds nor is it necessary. Just useful for speeds etc difficult to do on the public road. For idle and low/medium speeds you need to do this yourself - unless you have extremely deep pockets.

stevieturbo · Post by **stevieturbo** » Tue Apr 17, 2012 11:04 pm

It just simply needs tuned properly.

There is no reason mixtures and timing shouldnt be optimal at all times. That's the whole point of fuel injection systems

ChrisJC · Post by **ChrisJC** » Wed Apr 18, 2012 6:57 am

I notice on lots of fuel injection systems things like this on the air intake:

between the manifold and AFM.

I often wonder what they are for, perhaps pulses from the inlet confuse the AFM at certain speeds making it hard to tune....?

You never see them 'aftermarket', yet the manufacturers wouldn't add them if they didn't need to.

Chris.

DaveEFI · Post by **DaveEFI** » Wed Apr 18, 2012 7:58 am

MegaSquirt most commonly uses engine vacuum and throttle position to calculate air flow.

kiwicar · Post by **kiwicar** » Wed Apr 18, 2012 10:20 am

As you suspect Chris that is a damper that stops resonence in the inlet tract at a given frequency, they take a lot of time to develope, not somthing the aftermarket ever gets involved in.
Best regards
Mie