The settings have been well documented here as being .54 volts +/-.07 but I have just read a bit of a curve to this. I have a 1990 and my FSM states .36-.96 volts. In Gordon Killebrew's Vol.2 "Questions" he also states that for 1990-1 ONLY; the setting is .36-.96 volts with .72 as being normal and the TPS is non adjustable.
I was having a problem when my vette from start up on a cool morning or nite was sluggish and a definite lack of power till warm up then fine. There was no bad idle when cold. Not knowing the above at the time; I checked the TPS voltage and read .78. I had to drill the bolt hole in the TPS .06" larger in dia. to get down to .58. My vette did run better when cold. Tried .55 and slight symptoms were felt again. I bumped it up to .62 but have not tried it out yet as she is stored now. I have since read my above findings...note..just turned 15,000 miles.
Does anyone know why there is a difference in voltage settings for 1990-1 models???

 

That is a new one on me......didn't they go back to the MAP sensor that year instead of sticking with the MAF.....maybe that has something to do with it.

 

Yes; MAP / Speed density were the changes.

 

90-91 is a non adjustable tps. Because 0% throttle angle is still 0%, as long as it doesn't have voltage dead spots when tested, it has no real effect on fueling. All of the parameters in the prom (SD car)only deal w/% of tps vs. any of the fueling tables. A stock non-adjustable TPS for these years typically will read .59-.6+ closed throttle. Variances in voltage readings at idle can change in park/nuetral based the min. air setting/adjustment on the TB. (in gear vs nuetral will also change based on lowered rpm's).

 

I would be helpful if you listed the procedure you're using to check the voltage.

Jake

 

I have a plug in unit now...top wire black (-) ..next down red wire (+)..hook to multimeter..DC...turn ignition to the "on" position...read voltage FSM states .36 to .96 volts....check WOT reading making sure it is a progressive steady rise to over 4 volts .

 

it sounds as yout plug and method of testing is good, but you may want to do some addional trouble shooting. The tps voltage w/closed throttle in a 90-91 should not have any effect (once cycled on/off with the key). The is because the ecm (90-91) uses the TPS input as % of throttle/angle, not TPS voltage in the fueling parameters of the prom.

Since you mention performance is down on start up and before warmed up, is it possible that what you are experiencing is OL operation?
Did it do this last year when it started to get cold out ?
Has the min. air adjustment screw been re-adjusted ?

 

I bought my vette last June..2007(mileage was 10,504 miles) for my retirement this May. Didnt have a problem last year but didnt drive it much during the later cool nites. I had a stumbling problem this year even warm and power loss intermittenly but found that the lock down bolt on the distrubutor was loose and was at 0* initial timing...reset to 6* and that problem was cured.When I had my Xray scanner on; noticed the .78 volt TPS. Played with it and settled at .58 and it seemed okay. The air adjustment screw has NOT been touched as the plug is still in place. Ive run out of time as the vette is stored now and played with the TPS just before storage. I noticed that when I got it down to .55-.56 volts; it started slightly feel like before. I always did my road tests "early" in the mornings" for a few days to have same time results.When I cured the timing issue but the loss of power was still existing; the vette idled fine but when I punched it there was a noticeable lack of acceleration but it rev'd up fine but slower due to lack of power but at .58 volts ; it almost normal to normal --Only when cold but it ran FINE when warmed up.
Now this is a guess but at .78 volts---bad......at .56 volts starting to slightly feel problem....at .58 volts normal...my guess it would have to be in the low to mid .65 volt area. I will have to play with it to find my optimal spot.
Im not up to all the short forms yet..what do you mean by "OL" operation:o:o
Also; from doing the search function it seems that people are upping their initial timing to 8-10*...should I be looking at this also???
Thanks to all the helpful replies so far!!

 

well congrats on the low miler vette sounds like a nice car.
To start, I would guess you set base timing w/the est disconnected. If the timing is retarded some it could cause a lack of power particularly in OL (read on). Since this is one of the things you have adjusted I would have another look at this one. If you advance it maybe 2* it should not be a problem. But know this, advancing the distributer is a global change and not just at idle.
Air cleaner, fuel filter, possible restrictions in the exhaust, possible EGR operation (partly open or open all the time), fuel pressure, bad fuel, etc.etc. can all contribute, and may only seem to be more apparent before entering closed loop operation.

"OL" is short for "Open Loop'. Before your car is warmed up (approx.150* and your scanner will verify open or closed loop operation) it will operate in Open Loop. In this mode the ECM is using look up tables for AFR (Air Fuel Ratio), timing (with start-up ad-ons), MAT (manifold Air Temp) sensor (for temp. fuel add ons), CTS (coolant temp sensor) and various 'add-on' tables for IAC, timing, % of TPS etc. but, will not be using the input of the 02 sensor for fueling.
In closed loop the ecm can then make changes based on the input of the various sensors, against fixed "look-up" tables (fueling, timing, etc.) and from the input of the 02 sensor. (condensed version).

Aside from the actual properties in the ECM's memcal/prom (which I stated earlier the TPS voltage not having a bearing on this), I would be looking at other areas to resolve the 'sluggish' response you have described. Now if yours was not a 90-91 I would agree the TPS having an effect, in your case it shouldn't (operative word there, and obviously anything is possible) be having this effect.
It appears to me as though the poorer acceleration is in effect just in open loop, as you mention once warmed up the car performs normally. Looking at your auto x scanner here may help, by being able to 'see' all other parameters, which may help identify if the inputs from all other areas (mentioned earlier) are working properly etc.etc..and or, what the sensor inputs are, and what they are doing in Open Loop as well as closed loop. An FSM (Factory Service Manual)will help you by giving all the info for stock settings, and trouble shooting. Normally most would encourage you to use the search function. I'm not because every time I go to use it I get "data base" errors. This board had one of the best archives around.....if it lets you in.
sorry for the long post.........

 

Thanks for the response mseven. When I bought my vette last year being a finicky person; I immediately changed oil and filter(Mobil 1)....changed the tranny fluid and filter.....changed the fuel filter since I had the X brace off.......changed the antifreeze and upper and lower rad hose...did a throttle body bypass...changed the air filter and opened up the air box.I had a 1988 Formula 350 since new(son has it now) so I felt comfortable with the L98 engine. I then dumped a lot of fuel injector cleaner in and used 240 Sunoco (10% Ethenol no choice up here in Canada). Guess what..within 4 weeks lost a MULTECH injector and the others were going. I didnt realize the switch from Bosch which I was used to so had to order some Accel "silver tops" from Summit. I did the switch and hurt my lower back in the process but the operation was a sucess...the patient lived... but the doctor was crippled:o. With the info you provided me I am leaning to increasing the timing. Cant wait till spring now. I also put a s/s Magnaflow catback system in...put a new Catco hiflow cat in and rem'd the precats and sleeved the spots in.I checked my scan data in both open and closed loop and the only one that finally jumped out at me was the TPS.
THANKS TO ALL for the replies!!!!

 

So much I don't know about as far as SD, MAT cars, but I do know you don't have a CSI. What I do have is two questions I'd like to ask though are 1. have you checked the CTS? and 2. although I haven't heard anyone seeing a problem by doing a tb bypass, did this problem begin after you'd done it?

 

Sounds like the "new" exaust mods and injectors may be part of the equation that your struggling with. Feel free to adjust the timming to find a new spot were you car will be happier. You can adjust/advance timming how other CF members recommend to get yourself close to where you need to be....each car is a little different. Then play with the timming until you find were your car likes it the best. Find a nice patch of road and test your timming selection from 0-50mph.

 

All my changes were done the summer of 2007 as soon as I bought my vette. This problem surfaced this year in late Aug. and at this point I found the hold down bolt on the distributor was loose and only had 0* initial advance. This is why I will be leaning to initial timing as my problem as with the replies I have rec'd; my knowledge is gaining on Speed Density vs the Maf system that I was used to for the last 19 years until I bought my dream car. The throttle body bypass will only keep the incoming air cooler. On my 1988 Formula 350 Firebird I even rem'd the 9th injector and plugged the fuel rail and intake with a Accel plug kit that I got from Summit. Never had a problem in the winter during my periodical starts and found it started better in the summer as I feel it was overkill by GM especially during the summer soooo; OFF it came.

 

Oh I will for sure. I have the old original G-Tech and have been using it for years

 

lol, you know enough to understand the relevency of the CTS, and good call...did I put 'CSI' in somewhere?

to the OP, you're welcome...and yes Rick's mention of CTS is very relevant. Most of the parameters in SD regarding fueling, afr, etc. and in open loop uses the coolant temp for reference in the 'look up' tables (x' temp=x' afr, x' temp= idle rpm, etc.etc.). Which is also something to look at, since it is sluggish only when cold or on colder start-ups.

One of the things to also note is that w/SD strategy cars, is the in-ability to compensate very well for changes in the set-up. What may seem to be small changes (even w/exhaust, was the A.I.R. disconnected ?), particularly in fuel pressure changes and inj. swaps, has a greater effect on fueling (rich/lean when viewing the BLM_Block Learn Memory) than w/MAF based cars.

Another consideration here is the inj. swap. While necessary and even if using the exact same lb.rating (are they the same LB.rating ?) may not be giving the exact same results in fueling. Since they are from a different mfg., it might be enough to cause enough change for you to notice a difference in performance when cold.
However, when fully warmed, and in closed loop, it sounds as though the ECM is capable of compensating enough to allow good performance. If a slightly larger inj. was used other than 22.(stock for 90-91) say 23 or 24 .lb, this would account for that. It won't hurt anything, but the original programing is for 22. lbs., you would just be running a bit richer (vise-versa a 21. and it would be leaner). Next time you scan it look at the CTS. info when cold, as it is warming up, and you can also ohm check it. Additionally, when fully warmed and in closed loop, see what number the BLM (Block Learn Memory) shows, as it is an indication of rich/lean.

 

No Mick, you didn't mention CSI, we both know that ended in 89 . just mentioned it because this seems to be an OL problem, and was thinking not part of this cars equation. But the CTS could be something to look at.

 

I thought maybe it might have been my not so great typing skills....(hence why I need to do edits sometimes )

 

The BLM block learn does show a compensating rich condition (118) at OL with a Integrator of 128 due to 24# injectors(only ones I could get at the time) but they were done July of 2007 and added a AFPR to try and compensate ..at CL it is 128.. I was running a 170* stat as I switched from 195* when I changed the antifreeze. I thought this might be a little cool and went to a 195* stat BUT after the TPS change. It natuarally heated up quicker but no difference with the .58 TPS setting. I then dropped back to a 180* stat while at .58 TPS setting and still okay but at .56 TPS I started to feel a "slight" problem back. The reason for the 170* stat at the beginning as I felt at the time it would be okay as I ran a 160* stat on my 1988 Formula 350 F/Bird with excellent results.
My CTS readings on scan vs my dash gauge readings seem to be in line with each other.
Note...all my TPS checks and related test drive were all done in the early morning on a cold engine. Did not play with settings and recheck with a warmer engine. I wanted to keep my data checks using same cold start parameters.
Also...95% of my problem disapeared when I found the initial advance setting was 0* and went to 6*. It could be coincidence that playing with the TPS setting did a fine tune to smooth out the slight problem during OL thats why I feel your advise of bumping up the initial timing a bit is the way to go as you cannot believe the difference from 0-6* that it made. Never had a problem like this last fall at all until late Aug. this year and always with the same settings(except initial timing unknown) and the tie down bolt was "loose". I grabbed the distributer and it moved easily..caught me off guard but I had marked it and was just going to see how I would grab it....got a big surprise.

 

well in light of this new info. I would say this probably part of the cause of your sluggishness. Int. at 128, and a blm of 118 means very rich and the int. is not comping near enough to bring it to 128blm. To comp. a 118 blm to 128 blm, the int. reading would need to be in the upper 130-140 area in those specific load vs. rpm areas. Lowering the fuel pressure to drop 10 points to achieve 128 blm from 110, probably meant lowering the FP quite a bit. You need to be careful in how much fuel pressure you take away, as it can change the spray pattern of the inj. and atomization. Really, the best solution when increasing inj. size is to reprogram the memcal for a 24# so as to properly maintain all of the other fuel calculations in the prom. Remember inj. flow rates are rated at fuel pressure (usually 43.5-44.), and the original memcal is programmed for a 20.lb.
T. stat differences only will change how long it takes for it to get hot or totally warm up, once at a certain temp. it really doesn't matter any more.
However doing this can help, provided you lower the fan temps. as to engage the fans earlier as to maintain a lowered operating temp. (memcal tweak, or manual switch). Regardless, neither should have any effect on the TPS.
aaahhhh, post 9..............Coolant Temperature Sensor

 

MSEVEN....you GOT me :o ...did an edit after I realized what it was after posting when I did a search....I knew that already....just had a "arctic Blond" moment. I realize that I need the change on the e-prom but it ran great since I got her last year and then WHAM late Aug. this year the problem started. ..both at cold and hot. Like I stated previously; once the timing was changed it ran great hot and when cold it would intermittenly do it cold but ever so slightly but would clear within a few seconds and when I played with the TPS it was fine ..no intermittent at .58 but almost coming back at .56. In the spring I will bump up the timing and I need to do a mandated emission test and can compare the data to when the seller had to do a mandated emmission test to sell...here in Ontario,Canada they are strict like California. I feel confident that the reasoning to bump the timing up will cure the problem and if the emission test is not good; I will have to reprogram.
Thanks for your insight as I want to really get into these areas more now as Im retired and have more time to devote to my hobby.
I say again...DAMN!!! thought I got back in time to edit...You Got Me!!!