Should a TPS act this way?

corvettedave01

Active member
Joined
Nov 23, 2008
Messages
30
This is a very rough tune with the injectors. I think it's quit a bit too rich up top, but I got it idling pretty well. *What can I do to reduce the idle a little more?

I finally had time to mess with the vette today and found something very interesting that has been plaguing us all along.

I was able to consistently recreate the TPS issue that Chris pointed out to me a couple of times while he was dyno tuning it at Wichita Dyno. He just couldn't figure out how to consistently recreate the problem.
-Under the TPS calibration table, the tps value is consistent every time regardless of combination of actions with the throttle pedal. 0 to partial, to full, all very consistent, no problems. .47 to 3.9 volts if I remember right.
-However, in both the VE and base timing tables the following happens.
1. 0 to 100% throttle pedal is usually fine (not always, sometimes 80-90% tps when the pedal is 100%)
2. 0 to 50% to 100% pedal results in 0%-50%-70-90% TPS value on both the VE and base timing tables. I can recreate this problem consistently.
3. When I go back to check it out on the TPS calibration it is perfect with the gas pedal no matter what combination I put it through.

So...It seems that something internal in the computer is going wrong between the voltage reading of the TPS sensor, which is always correct to the posting of the TPS value on the VE and base timing tables.

Let me know what you think,
Dave
 
Dunno...I just checked mine tonight and the TPS reads consistant on both the spark and VE tables. The fact that your TPS sometimes reads <100% tells me that the throttle body/cable set-up may be loose.
 
Thanks for the response Gary. I thought about this at first too, but tested it. The problem is, if the cable was sticking then it would stick in the calibration graph as well and it NEVER does. Only in the VE and base timing tables does it 'stick'. An engineer with FAST contacted me and he is thinking about the problem as well as they haven't run across this before that he can recall. I have maintained all along the ecu is a problem and I think this pretty much indicates this is the case at this point anyway. I just wish I would have figured out the problem pattern before I spent about $6k to fix it, that was basically my supercharger setup dollars.
 
Thanks for the response Gary. I thought about this at first too, but tested it. The problem is, if the cable was sticking then it would stick in the calibration graph as well and it NEVER does. Only in the VE and base timing tables does it 'stick'. An engineer with FAST contacted me and he is thinking about the problem as well as they haven't run across this before that he can recall. I have maintained all along the ecu is a problem and I think this pretty much indicates this is the case at this point anyway. I just wish I would have figured out the problem pattern before I spent about $6k to fix it, that was basically my supercharger setup dollars.

I guess it could be a software glitch...... I thought you sent it to them for a check-out already?. So far, FAST customer service techs. have been helpful to me. Don't give up on the FAST system..on all the FI forums I have been on it seems to be one of the best.
 
Thanks for the response Gary. I thought about this at first too, but tested it. The problem is, if the cable was sticking then it would stick in the calibration graph as well and it NEVER does. Only in the VE and base timing tables does it 'stick'. An engineer with FAST contacted me and he is thinking about the problem as well as they haven't run across this before that he can recall. I have maintained all along the ecu is a problem and I think this pretty much indicates this is the case at this point anyway. I just wish I would have figured out the problem pattern before I spent about $6k to fix it, that was basically my supercharger setup dollars.

I guess it could be a software glitch...... I thought you sent it to them for a check-out already?. So far, FAST customer service techs. have been helpful to me. Don't give up on the FAST system..on all the FI forums I have been on it seems to be one of the best.

THAT turns out to be a software glitch in their system after some 6 grand of MY money, I would sue BIG TYME, for recovery of time and effort, not that I"d collect a dime in Florida anyway.....

another good reason to just use factory shit, and get a slight known program modification if necessary....150 bux for the cam dial in, and Git er Done.....

:crap:
 
Yeah, I did send the ecu in, but I really wonder what they did with it. I requested the ecu test data a couple of times and never did get it, so I'm pretty skeptical that they even looked at the tps or ran it in speed density mode, which has never worked worth a crap. Anyway, the engineer that contacted me seems willing to help, so I will see. I'm not holding my breat though after 16 months of frustration already.

I am getting this motor to idle at around 14.5:1 afr after turning down the fp and putting the 48 lb injectors back in. Got rid of my off idle hesitation completely as well. Probably would have with the 55 # injectors had I just turned the fp down from 50 to 43.5, but too late now.

A side note. I had to spend $600 on these 55# low impedance injectors because the motor was leaning out at 5k and we hadn't put a finger on the tps problem yet. Well guess what, when your motor is wot and your tps reading tells it to put only 70% throttle worth of fuel in it...it LEANS OUT. Ah well, just one of many problems that would have been avoided with a stable system.
 
Last edited:
Ask the FAST tech/engineer if he can link up with your pc while your ECU is on-line. He will be able to access your real-time data and you can show him the TPS problem. I lowered my idle/ no load afr's to 13.5 today and it smoothed out quite a bit. You may need to do that also, as 14.5 at idle the engine is bound to be a little cranky.
 
Ask the FAST tech/engineer if he can link up with your pc while your ECU is on-line. He will be able to access your real-time data and you can show him the TPS problem. I lowered my idle/ no load afr's to 13.5 today and it smoothed out quite a bit. You may need to do that also, as 14.5 at idle the engine is bound to be a little cranky.

with 8 throws, it WILL be 'cranky'.....:harhar::surrender:


And you know the bitch of it, drove across the bridge on Friday....not as bad as it was, but still kinda rough at idle....smoothed out nice in traffic though, pulling away from a light....

yesterday, hitting some stores, looking for my TV deal....it was smooth as silk at idle and all other times.....two nearly identical days in a row, same temps, same humidity, same traffic conditions except for that 8 mile run on the freeway.....

so go figger....WTF is going ON already.....drive me crazy, and so I get some shots over that comment..... I thinking of maybe try adding another fuel filter in there, can't get any worse, for sure....

still think the gas is 1/2 water along with that 10% ethanol crap.....
 
Last edited:
Thanks Gary. Yeah the engineer agreed with me and I'm sending the ecu in... again. If they can recreate the problem, they will finally see the ecu is a problem. If they can't...I have no idea where to begin. So you have the efi working on your 383/vortech blower setup already? How are you going to tune that under load?

MrVette. Yeah, I think your right, it seems there is something mechanical going on since nothing in the computer changed. I wonder if a sensor can be plugged up and cause things like that too?
 
Yep..got 'er up and running. Still learning how to tune...but picking it up nicely. On my ProCharged 383 I tune by logging either with the lap-top or the internal data logger. I am doing the road tuning today. I still need to wire in the boost sensor (2-bar map) to the ecu. After I get a good baseline tune I will hit the dyno and do a final hard tune. (I get no good full throttle data on the street as the tires are still spinning all the way through 3rd gear.) :shocking: That's the great advantage that efi has over a carb...the ability to do real-time tuning.
 
I presume you are using ONE MAP sensor, set for 2 bar, depending on your cam and static ratios, maybe 3 bar....

I can't see a plugged sensor as interfering with the TPS signal, something in the A/D converter or it's range set, something in the programming it's not picking up the full range all the time....

I really can't imagine why any A/D converter would have a issue with rapidly converting the signal for the CPU to work with....it almost sounds like the sample/clock rate of the converter is getting a bad or inadequate signal from the clock......something is definately a design fuck up.....

if the voltage is in FACT say 4 volts at a certain point, the the computer says it's much less, well, it's a internal problemo....I can't see any way around it.....

wonder if the RATE of change just overpowers the ability ......

gets to those comments I have heard about faster CPUs as being better somehow, but that thought drives my crazy, and most any computer clock is running at 10k times any possible engine speed, so it's sleeping in the shed instead of actually processing information.....

:shocking::ill:
 
Hey Dave, As you may know, the TPS and MAP sensors use a precision reference voltage generated in the ECU. For the Accel unit, that is a 5v reference and I am assuming the Fast unit is similar. That 5v precision voltage is referenced to a unique signal ground. The TPS is nothing more than a potentiometer with its wiper providing a resistor divided TPS signal back to the ECU. Again, its hard to troubleshoot electronics from afar, but there is a couple of things to look for.
If the potentiometer is bad it could be providing erroneous or noisy signal level back to the ecu for A/D conversion. If the 5v reference is noisy or loaded excessively it could also be a problem source. A noisy signal return would be equally bad. Make sure your 5v ref voltage is solid as a rock during all operation. Also the signal return needs to be noise free. Remember, multiple sensors use the signal ground. MAP, IAT, ECT, and possibly others. An Oscilloscope is about the only way to make sure.

wrt, to the symptom that indicates different TPS positions with respect to VE and spark, that could be easily explained by the fact that the two different algorithms may be sampling the TPS digitized signal at two slightly different instances of time. A noisy condition or a step function change is the signal due to a sudden load or noise could explain this condition. Again, very important that there are no extraneous ground currents or noise on the 5v and signal grounds.

Did you make your own custom harness? If you are using the FAST harness, make sure there is no wiring errors. The FAST engineers should test out the ecu electronics in this area for proper operation......one would hope.

Just my shot in the dark from afar.

Bullshark

BTW Gene, you need fast ECUs when you are incorporating some of the advanced techniques that control such things as precision sequential injector pulses, sophisticated multiple state Kalman filters used in optimal control techniques, and the next generation Predictive Model control I mentioned in earlier posts. As Big G stated in another thread,

The coming changes will be faster and more accurate control and to make the units more "user-friendly".

I know you won't believe me, but I bet your problem is not the lousy gas. :stirpot: And, with the limited user interface and tuning capability of that old GM... uh..stuff!... :kissass: ....it will be a lot harder to isolate. :D
 
I stuck another filter on the line there,....been all through the electronics, it's fuel related, no question .....

methinks I need pull the injectors, and stick them in a fuel rail...and test fire 4 at once same way I fired the HEI dizzy...to check my tach readings....

I bet some injector is bad/marginal....
 
I stuck another filter on the line there,....been all through the electronics, it's fuel related, no question .....

methinks I need pull the injectors, and stick them in a fuel rail...and test fire 4 at once same way I fired the HEI dizzy...to check my tach readings....

I bet some injector is bad/marginal....

Did you measure the delta temp at the exhaust ports with a IR temp gun? That might tell you something????

Bullshark
 
I stuck another filter on the line there,....been all through the electronics, it's fuel related, no question .....

methinks I need pull the injectors, and stick them in a fuel rail...and test fire 4 at once same way I fired the HEI dizzy...to check my tach readings....

I bet some injector is bad/marginal....

Did you measure the delta temp at the exhaust ports with a IR temp gun? That might tell you something????

Bullshark

Yes, and I dunno if it's the IR gun or what....never went with the T couple on account of lazy....I know the IR gun is fine at water temps...but no real way to correlate it other than transistor heat sink compound and the TC....

the temps are very inconsistant....at best....

:censored:
 
Well, I sent the ecu back in yesterday, will see if they can find that inconsistency. I just don't see it as a noise problem as one function of the ecu reads it perfect every time (calibration graph).
 
Well, I sent the ecu back in yesterday, will see if they can find that inconsistency. I just don't see it as a noise problem as one function of the ecu reads it perfect every time (calibration graph).

As has been noted by Bullshark, if the 5 volt line went funky, the program in the puter has NO idea that is the case, and sees the very first thing that falls is the TPS.....after that the MAP reading would be funky....or the MAF if you running one..maybe.....

course, i'ts also the ref point for the CTS,and incoming air even...

freeking 5 volt regulator chip can cause holey hell to come to pass.....:devil:



BTW, on my stupid car, I ran it outta gas yesterday....new gauges and I should know better.....thought I ran enough through the system on the roadside....but AAA got me flatbedded home, and the thing that's strange is when Linda/wife brought me 5 gallons of gas....the engine ran fine, then quit and refused to restart.....so I"m there on roadside not HEARING the fuel pump at all, which I can easy hear in my driveway with engine off, I have a convenient little clip lead thingy I can jumper two spots together and run the pump anytime off battery power.....looking at putting a permanent fuel pressure gauge on the engine, just to make sure of something....

but the fact that the engine started almost immediately, then stumbled and died, and failed to restart, and I went to my batter/pump jumper and ran it a goodly amount to clear any air.....I got totally mystified, as soon as I did this at home, the car runs fine NOW....

I still think it's freeking WATER in the damn gasoline, as I have fought this problem years ago down here.....

for one thing, there are rust stain on the inside of the tank....nothing super BAD, just brown stains...looks like rust to me....

but the carb'd 318 Dodge van don't care, I think I could piss in that tank and it would still run....

wife's little 4 cyl Ford Escort runs just OK, for the most part....but not a smooth as it can be sometimes....especially with the a/c compressor on....
I haven't gotten into that a lot though....just a observation at this point....
 
So Gene, what CR does your motor have? Is that an LT1 or TPI motor? Just curious.

:shocking::shocking::1st:

It is a hotrod....I got tired of the old larger runner/base L98 setup on there, and the engine was done 11 years ago....and through several head changes....NOW it has L98 stockish aluminum heads on the #113 castings...

call it a cammed up roller engine like a ZZ4....

with a highly modded up LT1 intake manifold on there, a buddy welded up the water jacket lines, and the dizzy mount behind....so it's a L98 dizzy....

52 mm tbody....same computer....LT1 injectors....L98 pressure regulator....adjustable....

I did it for just plain aggravation with dealing with and looking at the old style L98 setup....THAT most of all, which had been a thought for years....

and not being able to get at the injectors for easy trouble shooting...

NOW, life is simple....

AND when the SOB feels like running.....it's a RUNNIN'....hard....

but when that idle is rough....highly intermittent....comes and goes as it damn well feels like it....never a steady on miss, just a idle that shakes the car, and not even a consistant miss, like one cylinder...think it was a fucking dragster on a lo idle....damn cam not THAT wild....TPIS ZZ9.....

so I KNOW it's fuel related...just dunno WHY.....

going to drain the tank tmrw....and I just BET the thing comes out with a inch or so of water in the bottom....

and have NO idea how it get in there, except bad fuel in this area of Florida...which considering the very high groundwater is easy to believe...

when draining a concrete/gunnite INGROUND POOL, and the pool pops outta the ground because of weight reduction and flooding in water from UNDER The POOL.....I gotta think WTF is rong with local gas stations....

then so the Wife's '99 Escort runs more or less ok, but not as smooth as it could be....long story there...but unrelated to the vette....

meanwhile the '85 Dodge truck with 2bbl 318 in there, runs off pisswater....

Open for suggestions...I will beat this bitch....matter of time...

:1st::shocking::beer:
 
Water is heavier than fuel. What I do is remove the fuel line at the fuel rail and hot-wire the fuel pump. Fill a glass with fuel. If there is any water, it will settle to the bottom of the glass. If none is present in the glass, there is none in the tank.
 
Top