TPS at idle slow to respond when running

[cobra351w]

Hi Gurus,

This is my first post (i think) so bear with me for any fopars I might make !

So to start with the specifics:-
MS3X
firmwareDescription=MS3 1.4.0 release 20150709 19\:51BST

Ford V8 Windsor 351w running borla/TWM ITB stack
Penny and Giles Hall effect TPS

http://www.cw-industrialgroup.com/Produ ... 280DP.aspx

Setup:

Fully sequential Fuel and Spark off MSX board effective COP (using 2 x 4 coil packs)


Problem Description:-

If I calibrate the TPS , or observe the TPS with ignition on, engine not running, I get a very sensitive TPS reading down to 0.1 % if i move the pedal.

With engine running the sensitivity drops , there is no recognisable movement in TPS until at least 1.5 %, meanwhile the throttles have already opened, and the engine goes lean, only corrected when it actually reaches the next cell on the map.


History:

I had a major issue with both ECU dropouts (never resolved) and faulty TPS's last year whilst touring Europe, I never wanted to go through this pain again, and was on the verge of ditching the entire ECU, but decided to give it one last shot , so COMPLETELY rewired the entire loom, separated ALL sensor signals from any HT or injector signals , separated Signal ground out, running a decent thick wire .

The ECU dropout fixed , everything seems to behave very well.

The new TPS behaves perfectly throughout the rest of the range , except for this issue.

I put a scope on both Vref (4.88V) and TPS signal, no discernible noise or different between running or non running.
I tried changing the "averaging Lag Factor" down, but this did not make any difference?

I have a certain amount of electronics knowledge , and the only assumption I could make was there is some noise on top of the signal caused whilst running, that's playing havoc with the signal to noise ratio , because of the very small increments of pedal movement.

The other factor is the P & G sensor does give me a smaller ADC count throughout the range compared to the passive potentiometer type, so will try a new one of those today , to see if that helps?

Ultimately though , something whilst running is degrading the TPS signal, possibly off the scope range that I can see.

As usual with these type of issues , there was a similar post by robd on june 16 2012, with no resolution (or updated) .

I could try a different ground I suppose off the inlet manifold, but previous posts suggest this generally doesn't help.

Any help with this appreciated, as one week from now I'm touring Europe again, and although driveable (if aggressive) it would make the whole experience much nicer if I could get rid of the awful lean spot off throttle.

Regards

Rob

[DaveEFI]

Is it not possible to fit a conventional pot? A good quality conductive plastic track one has a very long life, compared to the earlier carbon track types.

A solid state position sensor does sound a good idea in theory - but I don't know if these can be used successfully with MS.

[cobra351w]

Dave,

Thanks for the reply, sure I'm going to try a wabash unit today, but the reasoning was the P & G units are far more reliable, as cant wear out.

just looking at the logs in highest res the ADC count jitter is only 1 count , which to me is pretty good ?

[cobra351w]

I also discovered something else , far more fundamental

It seems when the car was setup on the rolling road last year, the ignition table was setup against Alpha-N, when I created the new project, it must have been switched to speed density, so all the lookups are wrong .!

I have the original map, so can switch that back fortunately.

[DaveEFI]

Dave,

Thanks for the reply, sure I'm going to try a wabash unit today, but the reasoning was the P & G units are far more reliable, as cant wear out.

just looking at the logs in highest res the ADC count jitter is only 1 count , which to me is pretty good ?

Yes - a non contact position sensor does seem like a better idea. However, hall effect devices don't seem to last forever either. But good to know it's not the source of your problem.

[cobra351w]

Dave,

I think there still is a problem tbh, but I'll try the new TPS and check the results.

The Ignition table will affect the performance for sure, but still doesn't explain the lack of TPS sensitivity running?

Regards..

[cobra351w]

Just replaced the hall effect with a wabash one , very slight improvement, but i think that based on the slight increase granularity due to the ADC count.

Hall effect

0% =82
100%=689

Wabash

0%=34
100%=798

What slightly odd it seems to go through period of latency, leave to idle a while, the immediate response is slow, but give the revs a blip, then the next immediate response is good, and so on.

Are there any other tweaks that can make the TPS more sensitive, or overcome possibly poor signal to noise ratio?

I shall just have to drive it more aggressively I guess for now...poor me

Regards

[billr]

How is the TPS mechanically coupled to the throttle shaft? There was a recent thread where the OP eventually found a bit of slop in that coupling causing a similar problem. I am only familiar with the GM TPS arrangement, that is spring-loaded to eliminate any back-lash; seems like a good idea to me but apparently not all TPS are mounted like that...

[cobra351w]

Bill,

I checked that actually, as the new sensor has a slightly different profile on the receptical, so i shimmed it out so its really tight, so no movement at all.

Its definitely a signal level thing , so the only thing I can do is keep the two cells on the bottom row rich enough , that on opening the throttles a small amount , can overcome the lean patch, which makes my idle rich.

I'll see if I can get a more sensitive scope , and do a bit more hunting for noise, if anyone can give any tips on that it would be handy




Curious though, trouble is I cant say its hasn't always been an issue , but at least now I know the reason as to not being able to map it out.

Regards

[cobra351w]

A thought just struck me, which I will check tomorrow, this is an 8 stack driven by a centre wheel cable pull, that pulls both halves together.

The only difference when running would be the manifold would hold vacuum, thus I guess would make the butterflies more difficult to open.

So I wonder if actually one bank is opening first , letting in air which goes lean, before the second bank , which has the TPS attached to the end shaft registers any movement.?

That may explain the only difference I can think of, between running/non-running.

I'll update tomorrow.

Regards

[cobra351w]

After rebalancing the throttle bodies, it's mildly better, not ideal, as definitely still goes lean , but as on way to Italy on tour, it was the best I could achieve, if I get a chance I'll look into it further on return.

I have another post to write now regards failing o2 sensors?

[cobra351w]

Whilst I'm updating my other post, I thought I'd add a footnote to this one.
Initially when I re-balanced the throttle bodies, all seemed good , HOWEVER,this was not the case.!!


It turns out on the TWM/BORLA throttle body kits, use a linkage that allows misalignment in both axis , also preventing I presume, reduction in wear of the throttle shaft components , due to misalignment.

It was only when balancing yet again, I noticed the end throttle body that has the TPI sensor attached had free play , with respect to its pair, and the rest of the 3 pairs .

THIS alone was responsible for the lean spot , as the sensor was not moving with the rest of the them, plus also play in the others as well.

FIX:

Sounds a bit crude, but actually works very well, a drop of epoxy resin on one corner of each split linkage, which still allows flexibility, but takes up the free play in the link.


There were both down and upsides of this solution:-

1. I had to totally produce a new VE map
2. I now longer have a horrible lean spot, and as an out also my fuel economy and overall performance is much better.