ECM questions, sensors, TPS and MAP (Page 4/5)
fierobear MAR 14, 10:05 AM

quote
Originally posted by theogre:

When installed in a car... TPS often never reaches 5v by turning throttle to WOT on TB/TBI by hand or by pedal. Close to same reason doesn't see 0v @ idle.
Go by angle/% of throttle reported by a scan tool.
Turn throttle by hand should see 99-100% @ WOT even when not seeing 5V on the scanner or on meter on sensor.
But Press the pedal to floor often can't reach WOT because pedal and/or cable problems and more so for Fiero w/ 3-5 times cable length then front engines.

See my Cave, Throttle Cable




Good things to check, certainly.

The voltage readings I'm getting are .19v at idle to about .89v at 4,000 rpm. The SM says a code will be set below .2v (which does happen), and at idle voltage should be below 1.25v. But it isn't clear what reasonable normal range I should expect to see, idle to near WOT (I won't go WOT with the engine running)?

I had a suggestion from a fellow Fiero guy (Keith, the tail light guy) that I might have water in the gasoline. Initially, the car wouldn't stay running on the day of the incident. When I went to start it some days later, it started up and ran well enough that I could move the car. I'm wondering if I got some contaminated fuel, and the water is mixing and settling. Is there any fuel additive that would help ingest the water, or if after getting a sample of the fuel should I just drop the tank?

[This message has been edited by fierobear (edited 03-14-2020).]

PePe-LePu_For_2 MAR 14, 02:19 PM
Fierobear, did the red Formula run properly after you reinstalled its ECM?
Raydar MAR 14, 04:03 PM

quote
Originally posted by fierobear:
...
Is there any fuel additive that would help ingest the water, or if after getting a sample of the fuel should I just drop the tank?




I have heard that alcohol will tend to absorb water. I believe that's why E-10 - E-15 gum things up so badly when they're left to sit for a prolonged period.
With all of that said, there is a product called Drygas that may help.

https://en.wikipedia.org/wiki/Dry_gas

[This message has been edited by Raydar (edited 03-14-2020).]

theogre MAR 14, 07:19 PM

quote
Originally posted by fierobear:
The voltage readings I'm getting are .19v at idle to about .89v at 4,000 rpm. The SM says a code will be set below .2v (which does happen), and at idle voltage should be below 1.25v. But it isn't clear what reasonable normal range I should expect to see, idle to near WOT (I won't go WOT with the engine running)?

I had a suggestion from a fellow Fiero guy (Keith, the tail light guy) that I might have water in the gasoline. Initially, the car wouldn't stay running on the day of the incident. When I went to start it some days later, it started up and ran well enough that I could move the car. I'm wondering if I got some contaminated fuel, and the water is mixing and settling. Is there any fuel additive that would help ingest the water, or if after getting a sample of the fuel should I just drop the tank?

Key on but engine not running will run ECM and test nearly all sensors so can test TPS at WOT w/o wasting gas etc.

Low volt at idle can be iffy sensor etc plus iffy idle stop setup. But can't check/reset the stop screw on engine w/ other problems. A SHORT TERM "fix" is make a thin shim to idle stop screw tip to bump idle volts barely above the minimum TPS volts.

idle stop screw etc can wear and make low volts and bad idle. Worn throttle parts can leak more air thru shaft holes, close butterfly too much, Stop screw digs a hole in the lever or tip wears or both, etc. (Most T-shaft clearance are made loose and leak a bit of air normally. Is a problem when you see Oval shape holes.)

If you have enough water the pump will suck it then very likely no additive, including any formula "Drygas," will help.
Depending on label... "Drygas" is either Methanol or Isopropanol and using more then 1 small bottle in a car w/ full gas tank can cause bigger headaches because Both are Worse then Ethanol eating rubber parts etc. when used too much.

"Drygas" keeps small amount of water from freezing and blocking fuel lines etc. Car won't run if pump suck a lot of water even w/ "drygas" in the tank.
fierobear MAR 14, 11:48 PM

quote
Originally posted by theogre:

Key on but engine not running will run ECM and test nearly all sensors so can test TPS at WOT w/o wasting gas etc.

Low volt at idle can be iffy sensor etc plus iffy idle stop setup. But can't check/reset the stop screw on engine w/ other problems. A SHORT TERM "fix" is make a thin shim to idle stop screw tip to bump idle volts barely above the minimum TPS volts.

idle stop screw etc can wear and make low volts and bad idle. Worn throttle parts can leak more air thru shaft holes, close butterfly too much, Stop screw digs a hole in the lever or tip wears or both, etc. (Most T-shaft clearance are made loose and leak a bit of air normally. Is a problem when you see Oval shape holes.)

If you have enough water the pump will suck it then very likely no additive, including any formula "Drygas," will help.
Depending on label... "Drygas" is either Methanol or Isopropanol and using more then 1 small bottle in a car w/ full gas tank can cause bigger headaches because Both are Worse then Ethanol eating rubber parts etc. when used too much.

"Drygas" keeps small amount of water from freezing and blocking fuel lines etc. Car won't run if pump suck a lot of water even w/ "drygas" in the tank.



I was thinking about shimming the tps lever. I’ll give it a try. But, do you happen to know what the best voltage should be at idle?

[This message has been edited by fierobear (edited 03-14-2020).]

Raydar MAR 15, 09:36 AM

quote
Originally posted by fierobear:


I was thinking about shimming the tps lever. I’ll give it a try. But, do you happen to know what the best voltage should be at idle?




If memory serves, there is a little "tang" that sticks out from the TPS sensor, that is pushed when the throttle is rotated to "open". If you bend that tang just a bit, in the right direction, it will cause the TPS to show a higher voltage.
fierobear MAR 15, 03:42 PM

quote
Originally posted by Raydar:


If memory serves, there is a little "tang" that sticks out from the TPS sensor, that is pushed when the throttle is rotated to "open". If you bend that tang just a bit, in the right direction, it will cause the TPS to show a higher voltage.



I don't know if I'd be able to bend it enough, and it might cause a funky angle or for the tang to get caught on the throttle tang during it's travel. Might even cause damage to the sensor's internals. I'll probably just come up with a shim of some kind.
fierobear MAR 15, 03:44 PM

quote
Originally posted by PePe-LePu_For_2:

Fierobear, did the red Formula run properly after you reinstalled its ECM?



I haven't swapped them back yet. The Forumla has the GT ECM and vice versa. Formula is running well.

My next step is to do the above mentioned shim, but I'd like to get some idea as to a good starting/idle TPS voltage so that I can shim the tang to that point.
theogre MAR 15, 10:09 PM
Bending TPS now isn't good either for same reason Not to reset Idle screw.
Shim between throttle arm/lever and screw tip pushes idle a tiny bit to counter throttle wear etc Without being permanent or breaking the parts.
Use 1 layer, maybe 2, of soda can sides is likely to bump idle enough.

You only need to bump so TPS is above min limit. ECM doesn't care if TPS is between idle limits. When w/in those limits the ECM should use IAC to "fine tune" actual idle. You will see this in IAC Steps Counts at idle in data stream to scanner.
You also see Step Count change when engine running...
AT cars will change counts just putting the trans in R or D then back for P/N. "In gear" the count can be 30-45 steps higher vs P/N count.
Stick cars likely just drag the clutch a bit at idle when in gear. Should be instant change so drag the clutch to make engine to stall or heat/burn the clutch disk.
Even a small manifold vac leak that you control can likely change Step Counts.

Ever w/o reseting IAC ECM will try to use IAC to set idle but may not report step count until ECM has reset iac driving > 35mph etc. Or Step Count reported aren't accurate until then. ECM report IAC Reset in the data stream too.
PePe-LePu_For_2 MAR 21, 04:06 PM

quote
Originally posted by fierobear:


I haven't swapped them back yet. The Forumla has the GT ECM and vice versa. Formula is running well.

My next step is to do the above mentioned shim, but I'd like to get some idea as to a good starting/idle TPS voltage so that I can shim the tang to that point.



The reason I ask is what if the GT has broken its ECM. You might then swap in a known good one from the Formula only to break it as well. If the Formula’s ECM works when reinstalled, you could then test the GT’s ECM in the Formula.