Good Morning to all.

I have a question on why one would move the throttle position sensor to inline with the coolant temp sensor? Is it advisable and what are the issues or other problem it can cause, if any?

The engine had over 200K and decided to have a Jasper put in. It would run fine until it got to operating temp, actually it still runs fine at OP temp but it would have troubles stalling upon start-up when engine was at temp. Sometimes it would stall within seconds, or engine surge back-n-forth until put in gear then stall. You could get it going if kept pedal engaged quite a bit down to keep rpm up. If within the first 30 seconds you had to back off the pedal it would stall, after 30 seconds or so it would then drive fine. It started and ran fine when cold, and ran fine when at temp, was only the stalls and surges when starting at temp and the 30 seconds to minute after.

Mechanics were going crazy, trying to figure it out. Replaced an injector, distributor, coolant sensor - on top of the engine kit from Jasper that includes a lot of items. When finally resolved I was told they moved the TPS inline with the coolant temp sensor. I didn't have the time to go over it all with them when picked it up. They said the vehicle would believe it was running 30 degrees cooler than actually was. I asked if there were any issues this could cause to the car itself, was well as if would cause a CA smog test problem. They stated NO.

Apologies for the long description - I'll just report the questions again here:
why one would move the throttle position sensor to inline with the coolant temp sensor? Is it advisable and what are the issues or other problem it can cause, if any?

Also, would this mean the car would always be running in open loop and the ECM would never be making adjustments?

I did do some research last night, but wanted a better understanding if/when I go to question/hopefully not battle the mechanic. It is a independent garage that has done quality work on my cars before, including this one. I'm wondering if they just couldn't figure it out and took short cuts around the problem and not fix the underlying issue. Oh, prior to being "fixed", ECM was giving code "44" - they were aware. I haven't had time yet to check for any new codes or reset it back to remove the "44" code.


Thanks much for your time in reading this.

 

This article has a picture of the TPS and it is physically attached to the throttle body so how do you "moved the TPS inline with the coolant temp sensor". That just doesnt make sense. Why didnt they reset the code if they actually fixed the issue?
https://www.corvetteforum.com/forums...on-sensor.html

 

On the paper the stated "placed", I have a feeling what they meant is the wiring was redone to be inline with the coolant temp sensor? Unless they added a switch, I'll have to go take a look and get exact details on what was done.

I'll post when get that info. Thanks Mel for your reply

 

What I thought might be the case was. There is wiring going from the coolant temp switch up into the throttle body area.

I'm trying to understand why this would be done and what repercussions there could be to this. I have done research and learned some over the years but am more of a novice hobby to learn how it all works. I don't want to waste others time, just not sure exactly what this is doing or bypassing.

I have put an email to them to asked exactly what was done, what it is doing and why it was done. I'm just not overly confident I'll get truth.

Thanks again,

Tony

 

you read this article, if you have a voltmeter you could check the TPS

http://www.superchevy.com/how-to/468...system-tuning/

 

IIRC, the TPS and MAP both get 5 volts fromthe same pin on the ECM. The coolant sensor, MAP, TPS and ECM usually ground at the same place so to have an even ground plane.

Sound like they have the wrong coolant sensor or an open in the ground to the coolant sensor.

Code 44 has to do with the o2 sensor

 

Thanks. This is the reply I got back:

We wire a potentiometer inline with the engine coolant temperature sensor, adding resistance which the computer translates as a colder ambient temperature, thereby increasing the injector pulse width timing. Making the computer believe that the car is colder adding more fuel. This modification is completely within the computers parameters and is fully adjustable from full lean to full rich.

 

From the beginning it sounded more like a plenum vacuum leak or a bad EGR . That would explain why it needs to run rich but I never seen anyone alter the temp signal on a stock engine. I hate to say it but it looks like your mechanic is fixing the the symptom instead of fixing the problem. These engines run great in stock form as long as you fix the problem areas. If you mechanic used silicon on the plenum instead of the felpro gasket, this would be the first place I would look.

 

It seems to me like they are using the coolant temp switch to fake out the ECM on engine temp doing this? Would this actually bypass the O2 sensor all together?

 

I have never heard of this fix.you could change coolant sensor or change the thermostat.the 02 sensor reads the fuel air mixture.

 

I'm in agreement with Hugie, EGR issue or vacuum leak. Also, have the TB's been balanced? Out of balance TB's can cause the surging and idle hunting. "Fooling" the ecm into thinking the engine is running colder than it is isn't a good fix, it's just masking the real problem.

 

Thanks all for read and taking time in replying.

Quick update: The add-on work that was done (tricking ECM into thinking car was running at different operating temp that it actually way) was removed and put back to stock. They did a smog emissions test and found the secondary solenoid stuck open allowing air to to be pumped into exhaust when above 180 degrees. 02 sensor would show lean, forcing ecm to enrich fuel and flood engine, also said replaced lines to carbon canister as found some debris in it.

Problem is the issue is not resolved. The car operates fine except it will stall on startup only when already at operating temp. It tends to start and run when at op temp when started shortly after being turned off (5 min or so) but if await 30min, when turn key it will start and within a few seconds stall. You can get it going by keeping pedal down, and will run sluggish for 30 seconds to a minute (and likely stall if take foot off the gas pedal) but after that runs like just fine. So it's just the start-up and first minute where stalling occurs.

Not being a mechanic, but trying to use some deductive logic, it seem like something is either stuck like a valve that then opens after gassed for a bit or emissions backed up and gets cleared out after engine runs for 30sec to a minute. Would any of that make sense or fit in from a mechanics point of view?

I'm going to try an run some t/s after warming the engine. Like a 5, 10, 15, minute startup test. Then when stalls, start and rev the engine a bit in parl for 30secs or so and see if it can be put in gear without stalling.

Oh, they must have cleared the codes, as when picked it up only codes showed were 12, no more 44 codes. Even after it stalls now when warm, no codes register.

Thanks again and any views/suggestions appreciated!

 

So the results of my tests were what I thought would happen, but not sure what it means. To me it looks like some sort of emissions clearing problem. i drove the car to operating temp about 10 minutes, up to freeway, off one exit (mile) and back. Say 3-4 miles total.

After 5 minutes the car started, idled in park and did not stall when put in gear.
After 10 minutes the car started, idled in park but stalled when put in gear.
after 20 minutes the car stalled seconds after startup.

I check ECM no codes.

I started the engine, gassed until idling between 1000-1500 for 10 seconds, let off gas almost immediate stall.

Started engine again, gassed until idling between 1000-1500 for 40 seconds or so, let off the gas and it idled just a tad bit rough but not a lot, dropped in gear and stayed running.

Thanks again,

Tony

 

So the results of my tests were what I thought would happen, but not sure what it means. To me it looks like some sort of emissions clearing problem. i drove the car to operating temp about 10 minutes, up to freeway, off one exit (mile) and back. Say 3-4 miles total.

After 5 minutes the car started, idled in park and did not stall when put in gear.
After 10 minutes the car started, idled in park but stalled when put in gear.
after 20 minutes the car stalled seconds after startup.

I check ECM no codes.

I started the engine, gassed until idling between 1000-1500 for 10 seconds, let off gas almost immediate stall.

Started engine again, gassed until idling between 1000-1500 for 40 seconds or so, let off the gas and it idled just a tad bit rough but not a lot, dropped in gear and stayed running.

Thanks again,

 

when it does idle it idles high.should be around 700rpm.i would check egr and for vac leaks.

 

Thanks Terry.

Apologies for the confusion. It does idle 700-800, when I stated idling above at 1000-1500, it was idling there because I had the pedal engaged running it that high. I do that for 40 seconds or so when starting after engine warm, and then take the foot off the pedal, then it won't stall. Overall when it idles it does so properly.

 

so you are saying that for the first 60 seconds after starting it does not run right ,then it is okay?

 

That is correct. When already at operating temp and sitting for a while it will start but stall within seconds unless you give it throttle for 40 seconds. At that point it is fine.

 

Also, I wiped inside of each muffler tip and each had dark black soot, kind damp not like powder. Is that normal.
Taking it back in tomorrow.

 

has fuel pressure been checked?i would take air cleaner off, restart the car,look at injectors and see if it is starving for fuel.