TPS readings??
Turbo Mini Forums

Im having some problems with my TPS I think. When I turn the engine it bounces off the limiter straight away, not good considering its a rebuilt engine.
Its running a Canems ECU, which during setup you calibrate the TPS, according to the software everything is good, the Throttle Closed is the lower reading than the throttle open.

Turn engine on and it starts banging off the limiter, I dont even touch the throttle so its not me!. There is a diagnostic setting with the ECU and it shows the max TPS reading in % was 100. So Im taking this as the fault, it thinks the throttle is at WOT when its not. But everything in the software is programmed OK. The only thing I can think of is the wiring is back to front and the sensor is reading in reverse, which in its self doesnt add up as the Plug can only fit one way, and the readings when I calibrated the sensor were okay.

Any thoughts?

It will only rev if it can get air.

What inlet are you using?

Have you got an IACV?

Have you tried winding down the idle?

Is there an air leak?

Edited by Paul S on 10th Jun, 2011.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

as above, air is getting in somwhere, and from the sound of it quite a bit of it!

Thats what I was thinking but the butterflies are closed, to idle is set as low as I can go
Ill go poke around for a leak but Ive closed off anything that wasnt used as a Take off. Also the rev limiter was set at 4k (Ive changed that to 2K now in light of what the engine is doing) surely it would have to be a fairly large leak to run that sort of RPM randomly?

Inlet is custom made and the Throttle bodies are Mikuni 34mm.

No IACV valve either

As above ^^^

The TPS readings to the ECU have nothing to do with the speed the engine will "idle" at, the TPS readings to the ECU simply tell the ECU to calculate things such as acceleration enrichment (assuming canems runs a proper speed/density programme).

Something is letting far too much air in and the ECU is simply providing the fuel to match.

For example a stuck open or wrongly wired IACV will allow the engine to reach the rev limiter under no load conditions (well it did on mine when I had it wired backwards at first and it drove fully open instead of closed).

If canems has closed loop idle control, turn it off temporarily and blank of the IACV and see what happens.

EDIT - just seen, no IACV.........

Air from somewhere else then, the ECU doesn't control air flow if you have no IACV....

Edited by Rod S on 10th Jun, 2011.

Schrödinger's cat - so which one am I ???

Out to the car I go, I suppose it has to be something quite obvious to rev that high?

Block the main inlet to the throttle body(s) with the palm of your hand(s) and get someone else to start it - you will "feel" if the air is going in through the throttle bodies or being sucked in somewhere else.

Schrödinger's cat - so which one am I ???

Also any chance of a pic,

(says a thousand words and all that....)

Pictures of throttle bodies:









I have removed all the take offs and plugged them apart from the vacuum advance. I tightened the bands that hold the TB onto the rubber part of the inlet. I made sure the maniford nuts were tight. I tried it there again and its doing the same, There couldnt be many more places air can be getting in at such a rate??

Excuse the mess, Im just looking at getting it going, then Ill tidy up!

First off, I would straighten up the injectors and get the O rings properly seated.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

I'm with Paul inso much as those injectors are well skewed and possibly not sealed.

From the layout you can't really block the inlets by hand (my old skool trick) so tape them up with something substantial (ie, fabric re-inforced duct tape) and then start it - you will hear where the air is getting in then.

Schrödinger's cat - so which one am I ???

The injectors are skewed because theres a mount on the TB that the Fuel rail bolts to and the holes are drilled not quite right, the result is the injectors sitting like that. Ive tried to get them to fit straight when I was fitting them and the above is the best I could get them. Without having done this before or Ive no idea how the injectors look after they are seated. I pushed them in and felt the o rings compress, then they stopped so I presumed this is how they seat. Looking at the TB there it seems the shoulder our the injector should be touching the TB however on mine they are a CM or so off.

stick a big dob of vaseline or grease round the bottom of the injector and see if it vanishes when you fire it up....

Ideally the injector should NOT be "seated".

Between the recess in the inlet and the recess in the fuel rail, the injector should have a bit of movement back and forth and you should be able to rotate it without it leaking. This allows for expansion with heat etc.

The seal is made by air/fuel pressure on the O rings, not them being forced into place.

But they only seal if the injectors are at 90 degrees to the recesses.

Block the TB inlets like I said and run it and see where the air is getting in.

Schrödinger's cat - so which one am I ???

Ah right, the injectors were free to move and turn allright. I can see how I can get them to 90 degrees too, Wont look good but it should work.

I covered up the Inlets and there is air getting in somewhere, ill have to wait for somebody to get home to crank the engine so I can give it a good check, its hard with your left hand stuck in the car! Its quite alot of air too.

It seems the air(or fluid) I heard was from the injectors. It stopped when I disconnected the fuel pump.

With the fuel pump disconnected and the TB covered I couldnt hear anything, so back to square one.

Would an empty tank <5L of fuel be an issue? The pump should be well primed after all the turning over I did to get oil pressure.

Heres the fuel map that Im running, its all gobble de gook to me, I have to sit down and learn it all.

Edited by ciaran on 10th Jun, 2011.

Tank level not an issue - it runs.....

Pump is not like a carb pump, it runs when the ECU tells it to run.

Fuel map (VE table) not relevant to your problem.

You will hear noise from the fuel rail with the ECU and hence pump running, a different noise to the air you are apparently sucking in.

If you have covered the TB inlets and it still runs there is a lot of air going in that isn't going through the TBs.

Another old skool trick to find where is to run it with the Tbs blocked and spray something flammable (ie, a plumbers blowtorch, which is just butane or propane, but unlit) around and see when the engine speed changes.

BUT BE CAREFUL - anything like butane can ignite on a hot exhaust.

Schrödinger's cat - so which one am I ???

Are you sure that the tape around those vacuum ports is actually sealing them up?

Any idea where those injectors come from? They look very odd.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Its a rebuilt engine, I really dont want to be running it at stupid RPM, or letting it bounce off the Rev-Limiter while I figure out where the air leak is.

Is an air leak the only possible way the engine would be running in such a way? What I mean is that its such a large leak and I cannot find it around the TB and manifold area. Could it be getting in another way? No way air could be getting in with the fuel along the fuel system and injected with fuel through the injectors for example? I really dont want to end up wrecking my newly built engine!

Injectors are Delphi injectors P/N 17113738. They are quite highflow at 525 Cm3 per min.

I double taped them so they are as sealed as they can possibly be.

Are the butterflys being drawn open due to the return spring being too weak or missing

Edit to add, do the butterflys seat properly when closed?

Edited by Ratty on 10th Jun, 2011.

Check the usual problem of different manifold flange thicknesses.

I've check on my Mikunis. The only possible inlets downstream of the butterfly are the injector or the vacuum port. So if they are OK, then it must be one of the flanges.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

The butterflies do seat when closed, but the butterflies being drawn open would make some sense, and wound add up with the confusing readings off the TPS.