EFI MAP sensor readings after TTP 904s kit - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 9 (permalink) Old 04-02-2019, 10:01 PM Thread Starter
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EFI MAP sensor readings after TTP 904s kit

Hey guys just looking for some feedback here. I've recently installed a TTP 904s big bore kit along with a ported head and +1mm intake valves. I have been having some issues with the bike stalling while idling or on clutch in when fully warmed up. That issue is more prevalent when the engine temperature gets up over 250F.

I've replaced the MAP sensor tubes with one piece silicone tubes with clamps. Idle is set around 1000-1100. I've verified throttle bodies are in sync and TPS is set to .6v. I noticed while plugged into Tune Loader that the MAP reading seem a little on the high side at 430 hPa. My research here on the board for a 865 bike has led me to posts saying they should be at about 360-380 hPa. I'm wondering if increasing bore size and head airflow increase changes the manifold vacuum numbers (ie is this normal?)

Any input is appreciated. Here's a screen shot from Tune Loader:

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post #2 of 9 (permalink) Old 04-02-2019, 10:41 PM
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I'd have expected an increase in engine vacuum probably due to the higher displacement, the raised compression ratio of the 904 kit and also the extra ignition timing advance that the new TTP tune map provides (I assume you also have tunes 3 or 4 installed). It's a healthy reading consistent with a good combustion process and beautifully balanced, don't think that's the cause of the stalling.

Try it out for a bit with a higher idle speed, something closer to 1100 rpm. As the throttle plates would be slightly more opened for a higher idle, that vacuum reading would also drop a little.


We'd welcome @PieMan comments on the above.

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post #3 of 9 (permalink) Old 04-02-2019, 11:40 PM Thread Starter
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Thank you Forchetto. I did not think they were related either but had not seen those numbers and wanted to rule out any MAP issues. Your explanation makes sense and I won't worry about it. I am running Mike's Tune 15 for the 904s kit. Forgot to mention I have 790 cams installed as well. I will try bumping the idle up some and see how she does.

One more question. Would a slightly lean condition cause the stalling? I'm wondering if the larger valves and porting may have an affect on the idle fueling. I've noticed that before it cuts out the idle will drop down to around 8-900 or so for a few seconds.

I'll be heading to the dyno soon to do some partial/full throttle runs to send to Mike so he can tweak the tune so I should have some solid answers on the fueling at that time.

Thanks again.
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post #4 of 9 (permalink) Old 04-03-2019, 04:41 AM
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Originally Posted by MRFreeze View Post
One more question. Would a slightly lean condition cause the stalling? I'm wondering if the larger valves and porting may have an affect on the idle fueling. I've noticed that before it cuts out the idle will drop down to around 8-900 or so for a few seconds.

I'll be heading to the dyno soon to do some partial/full throttle runs to send to Mike so he can tweak the tune so I should have some solid answers on the fueling at that time.

Thanks again.

It could well be a little lean. If it continues doing that I'd mention it to Mike so he can enrich the fuel a bit at the low end.
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post #5 of 9 (permalink) Old 04-04-2019, 11:26 PM Thread Starter
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Bumped the idle up to about 1200 today and rode around for an hour or so and not a single stall. Here's hoping it was as simple as that.
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post #6 of 9 (permalink) Old 04-07-2019, 07:06 PM
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my similar spec 904 idle is around 980-1050rpm and shows an idle vac of 360hpa,

so my guess is that you have an air leak in the inlet tract. (this could also be the reason for the stalling, if there is an air leak you end up backing out the idle screw to compensate)
common places for intake air leaks are :- inlet manifold rubber to throttle body, inlet manifold to head (poor o-ring seal)

a screen shot of the L tables at idle may help diagnose if the idle is too lean.

also where is your intake air temp sensor located?, if you are using pod filters the location of this sensor is very important to the fuel trim.

who wudda thought id wanna bonneville!

Last edited by mike-tt special; 04-07-2019 at 07:22 PM. Reason: to make it read betterer
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post #7 of 9 (permalink) Old 04-08-2019, 03:44 AM Thread Starter
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Thanks Mike for the reply. I'll double check the IM boots first as checking the o-rings will require some disassembly. We used new ones on install.

On the air leak theory, I would expect that the MAP readings would have been different between the two sensors after the rebuild with a leak. They were initially 420/430 so only a very slight adjustment to the balance screw was necessary. It seems unlikely they would be leaking the same amount to cause such similar readings although it is certainly a possibility.

I'm using the TTP ARK so the temp sensor is located on a tab behind and in between the two filters.


Question on Tune ECU. I'm using the TTP version so I don't have access to the other table values and sensor readouts. I tried going to the TuneECU site but it looks like it's down. Is there somewhere else to download it from?

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post #8 of 9 (permalink) Old 04-08-2019, 07:47 AM
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The flange of the relatively soft alloy manifolds are the likely source of an air leak, especially if they have been ported to match a ported head or you are running OE throttle bodies and pod filters without a TB support,

What happens is the alloy manifolds distort at the flange due the unsupported weight of the TB's. this was the main reason for the TPUSA billet manifolds.

I had this problem when I was still running the std TB's and pods without any means of TB support, I cured it by applying three bond gasket sealer to the o ring groove and mounting face of the alloy manifolds, and using a cable tie between the rear TB's spacer bar and the cylinder head to frame rear brace to support the TB's

Your intake air temp sensor is in a good position but it is worth checking it is working correctly, if it has failed it would throw up a MIL error code but not if it's inaccurate , I seem to remember forchetto did a thread on checking this sensor.
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post #9 of 9 (permalink) Old 04-11-2019, 02:29 AM Thread Starter
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Thanks Mike. Ill double check the boots and manifolds. I already have the TBs zip tied as you suggested for support.

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