Will bad TPS shut down injectors?

1965GTFB · Mar 21, 2009

92 LX 5,0 vert bought from 1st owner(uncle) 4 yrs ago with 17k miles, now at 68k
Original problem is it would crank but not start. Would fire after spraying carb cleaner down the TB.
So here is the latest:
Installed the following in this order:
New fuel pump.(pump was not starting with key on)
New fuel pump relay.
Still crank, no start.
New Ignition Module.
New cap & rotor.(was doing this any way still had orig. on car)
Fuel pump now starts when key is on and keeps running, never shuts off. Fuel pressure is 42 psi.

Went thru the whole "Cranks OK,but No Start Checklist" again
and every thing checked out OK except the TPS. Check list says The checklist says TPS green wire voltage should be .5-.99 with key on not running closed throttle. Also read on another post that at WOT voltage should be 4.84. My voltage is .23 at closed throttle. Voltage increases smoothly as throttle is opened but only goes as high as 1.32 max. Even with the TPS off the intake so I can turn it manually as far as possible 1.32 is as high as it will go.

So, does this mean the TPS is bad, and even though there is 12 volts to the injectors they are not firing due to an incorrect voltage reported from the TPS? As before it will fire briefly after carb cleaner is sprayed down the throttle body. So it seems like the injectors are just not firing.

From the check list it seems like this is the last thing it could be. Ready to go pick up a TPS today unless I hear that might be a waste of $.

I have read about the ground problems some have had and was told that even with 12v to the red injector wire it still might not fire becuse of some thing on the ground side. Is what is the best way/place to check the ground that could cuse this?

Thanks for all the help folks.

f8tlfiveo · Mar 22, 2009

when you crank the motor did you try flooring the gas pedal as you are turning the motor? i was having a similar problem, so i started swapping parts from my brothers car and it ended up being the idle air control valve (iac). my car would start if you floored the pedal while you cranked the motor.

HISSIN50 · Mar 22, 2009

The injectors receive constant accessory voltage and the ground is modulate from the EEC (the ground acts as the on/off switch). A noid light is a quick and easy way to check an injector for pulsing.

I remember a decent TPS thread from awhile back. Maybe run through some of the tests and see what makes sense. Might save some cash. Good luck.

http://forums.stangnet.com/772242-cant-get-tps-voltage-above-15-volts-part-2-a-2.html

ID89GT · Mar 23, 2009

Yes a bad tps can prevent a car from starting. Will act like its in clear flood mode and won't trigger the injectors.

1965GTFB · Mar 23, 2009

Here is the latest and it is odd but might clear some thing up.

So today went back to testing the TPS by probing the connector with safety pins like I had done before.
Orange wire 1.47v - s/b 5v
Green wire .23v closed - 1.37v WOT s/b .9ishv - 4.84v
Black wire .01v(a suggested voltage drop check)
I loosened the fire wall ground and retighten it, no change. With the TPS connector apart voltage is the same on the connector leads.

So with the key still on and the fuel pump running non-stop I start reading some good info from another jrichker reply to a post. It's been maybe 4-6 minutes and all of a sudden my wife/helper says "hey the fuel pump stopped running. I was 10' from the car with nobody touching any thing. I come check and I now have .75 at the TPS green wire with closed throttle. I adjust it as far as it will go to .92 and check the WOT voltage and it's 4.7ish.

I crank it and it starts and idles fine(except for the valvetrain ticking that was never there before I'm thinking the sort of start and stumble buck and snort action from using carb cleaner in the TB during the check list testing may have screwed some thing up). Took the rpms up to just under 2k and few times no problem(except for the ticking).

I'm checking the ticking with my steathascope(sp)(it's #1), it's been running about 3-4 min and it dies. Voltages are back down to the low levels before it would start and it won't start again.

I giggle, disconnect and reconnect and generally mess with every thing I touched before, no change. Won't start. I give up start some yard work and seriously talk about selling it.

Give up have dinner. After dinner I decide to go out, turn the key on let the fuel pump run and check back a minimum of 5 min later. Sure enough pump has stopped and it starts(still ticking. Let it idle for about 6-7 minutes, never dies. Run the rpms still idles fine. Turn it off, key back on, pump stops after a few seconds, starts fine, 5 or 6 times. What the heck?

It was too late to drive it down the street to test, maybe tomorrow. I wouldn't consider it fixed and trust it at this point. As it is I may now need to pull the head to see if some thing is damaged on #1.

jrichker · Mar 24, 2009

As with all checklist procedures, start at the top and work your way down. Do not skip any steps, as the results of the next test depend on the last test having completed satisfactorily

Theory of how it works:
The computer supplies 5 volt VREF to power 3 sensors. They are the TPS, EGR and MAP/BARO sensors. The use of a tightly regulated voltage insures that all sensors are accurate over a wide range of operating temperatures. Note that the VREF orange/white wire supplies two engine mounted sensors (TPS & EGR) and one firewall mounted sensor (MAP/BARO sensor). VREF also powers all the electronics inside the computer.

Tools needed:
DVM with good batteries. Know the difference between voltage (volts) and resistance (ohms) and how to measure them with your DVM. Make sure you know how to read voltages and resistances with you meter. Some DVM’s auto range and others require you to select the range. Be sure you understand the range selection process if your DVM does not auto range. Do not touch the probe tips while making resistance measurements. If you do, your measurements will be very wrong.

Two or three big safety pins. You may need them to probe the electrical connector plugs from the rear. Keep in mind that it may require some effort to make good connections to use your DVM. Flaky or intermittent connections can lead you down the wrong path.
#2 Philips screwdriver
¼” flat blade screwdriver.
5/16” socket
¼ drive ratchet
3” long 1/4 “ extension.
3/8” ratchet
10 MM deep socket or 10 mm socket & 3” extension.

Getting started:
Verify that VREF is good:

1.) The fist step is to dump the codes: if one of the sensors is shorting VREF to ground, you will get codes 22 (MAP/BARO sensor), 63 (TPS sensor), and 31 or 32 (EGR sensor). You will get all the codes if VREF is shorted to ground, not just one or two of them.
2.) The next step is to determine which sensor is causing the low VREF voltage.

A.) All sensors connected and installed correctly. Ignition off:
Locate the MAP/BARO sensor on the firewall behind the upper intake manifold. Insert one safety pin in the rear of the electrical connector where the black/white wire is connected. Insert another safety pin in the rear of the electrical connector where the orange/white wire is connected. Make sure the safety pins do not touch each other or metal parts of the body or engine. Connect the DVM or meter to the safety pins. If your meter is polarity sensitive, be sure that it is connected correctly: positive to the orange/white wire, negative to the black/white wire.

B.) Turn the ignition switch to Run, but do not start the engine. Note the voltage: it should be between 4.5 and 5.5 volts. If it is within range, go to step 5. If it is over 5.5 volts, go to step 7

C.) If the voltage is less that 1 volt, turn off the ignition switch and ground the DVM or meter negative lead to the battery post. Turn the ignition switch to the Run position but do not start the engine. Recheck the voltage readings. If the voltage reads 4.5 to 5.5 volts, the VREF is good and the signal ground to the MAP/BARO sensor is bad.

D.) If the voltage is still below 4.5 volts, turn off the ignition switch and disconnect the electrical connector from the MAP/BARO sensor. Turn the ignition switch to the Run position but do not start the engine and recheck the voltage readings. If the voltage reads 4.5 to 5.5 volts, the VREF is good and the MAP/BARO sensor is bad. Time to replace the sensor. You will find that you will get a code 22 if the MAP/BARO sensor is bad. Leave the MAP/BARO sensor disconnected until the other sensors have been tested.

3.) TPS sensor connected and installed correctly. Ignition off:
The TPS is mounted on the top side of the throttle body. Insert one safety pin in the rear of the electrical connector where the black/white wire is connected. Insert another safety pin in the rear of the electrical connector where the orange/white wire is connected. Make sure the safety pins do not touch each other or metal parts of the body or engine. Connect the DVM or meter to the safety pins. If your meter is polarity sensitive, be sure that it is connected correctly: positive to the orange/white wire, negative to the black/white wire

A.) Turn the ignition switch to Run, but do not start the engine. Note the voltage: it should be between 4.5 and 5.5 volts. If it is within range, go to step 4 to check VREF on the EGR sensor.

B.) If the voltage is less that 1 volt, turn off the ignition switch and ground the DVM or meter negative lead to the battery post. Turn the ignition switch to the Run position but do not start the engine and recheck the voltage readings. If the voltage reads 4.5 to 5.5 volts, the VREF is good and the signal ground to the TPS sensor is bad.

C.) If the voltage is still below 4.5 volts, turn off the ignition switch and disconnect the electrical connector from the TPS sensor. Turn the ignition switch to the Run position but do not start the engine. Recheck the voltage readings. If the voltage reads 4.5 to 5.5 volts, the VREF is good and the TPS sensor is bad. Time to replace the sensor.

D.) If the voltage is still below 4.5 volts, Leave the TPS sensor disconnected until the other sensors have been tested. Then go to step 4

4.) EGR sensor connected and installed correctly. Ignition off:
The EGR is mounted on the back side of the EGR valve. Insert one safety pin in the rear of the electrical connector where the black/white wire is connected. Insert another safety pin in the rear of the electrical connector where the orange/white wire is connected. Make sure the safety pins do not touch each other or metal parts of the body or engine. Connect the DVM or meter to the safety pins. If your meter is polarity sensitive, be sure that it is connected correctly: positive to the orange/white wire, negative to the black/white wire

A.) Turn the ignition switch to Run, but do not start the engine. Note the voltage: it should be between 4.5 and 5.5 volts. If it is within range, go to step 5.

B.) If the voltage is less that 1 volt, turn off the ignition switch and ground the DVM or meter negative lead to the battery post. Turn the ignition switch to the Run position but do not start the engine and recheck the voltage readings. If the voltage reads 4.5 to 5.5 volts, the VREF is good and the signal ground to the EGR sensor is bad.

C.) If the voltage is still below 4.5 volts, turn off the ignition switch and disconnect the electrical connector from the EGR sensor. Turn the ignition switch to the Run position but do not start the engine. Recheck the voltage readings. If the voltage reads 4.5 to 5.5 volts, the VREF is good and the EGR sensor is bad. Time to replace the sensor.

D.) If the voltage is still below 4.5 volts, go to step 5 to check for wiring faults.

5.) VREF less that 4.5 volts with all sensors disconnected:
Disconnect the battery negative cable at the battery. Remove the passenger side kick panel and then loosen the 10 MM hex bolt that secures the computer wiring harness connector to the computer. Measure the resistance between pin 26 on the computer and the orange/white wires on the MAP/BARO, TPS and EGR sensors. You should see less that 1.5 ohms on each of the orange/white wires and pin 26. More than that indicates wiring problem.

Computer wiring harness connecter as viewed from the pin side.

The 10 pin connectors that join the engine fuel injector harness to the main harness are prime suspects.

Notice that pin 1 on the black connector is VREF. If this pin has a bad connection or broken wire, both the TPS and EGR will have no or low VREF voltage. A high resistance on only one wire is an indication of a broken wire or bad connection inside the fuel injector wiring harness.

If the above resistance test passes, move the meter lead from pin 26 to the ground point next to the computer. Then measure the resistance between the orange/white wire on any of the sensors and ground. You should see greater than 1 Megohm or an infinite open circuit. Reconnect the sensors and the computer, reconnect the battery negative cable to the battery.

6.) At this point, you have verified that all the sensors that use VREF have the proper supply voltage. If you still do not have proper VREF, then the problem is inside the computer. This is a replace the computer with a known good unit and retest to see if you get the same codes 22 (MAP/BARO sensor), 63 (TPS sensor), and 31 or 32 (EGR sensor). All the codes should have cleared unless you have some faulty sensors.

7.) VREF exceeds 5.5 volts:
Disconnect the battery negative cable at the battery. Remove the passenger side kick panel and then loosen the 10 MM hex bolt that secures the computer wiring harness connector to the computer. Pull the wiring harness connector down so that it disconnects from the computer. Then measure the resistance between the orange/white wire on any of the sensors and pin 1. Then measure the resistance between the orange/white wire on any of the sensors and pin 37. You should see greater than 1 Megohm or an infinite open circuit in both cases. Less than 1 Megohm indicates a wiring problem.
If the resistance check is good, then the problem is inside the computer. This is a replace the computer with a known good unit and retest to see if you get the same high voltage readings. If you do, then your DVM may be whacko…

VREF is verified as good, sensor output is still low:
8.) One or more sensors get a low output voltage code (63 - TPS sensor, or 31 or 32 - EGR sensor). After you have replaced the sensor and are still getting a low voltage code or low voltage reading, it is time to go hunting. By completing steps 1-7, you have verified that you have good VREF and it is not a cause of your problem.
Disconnect the battery negative cable at the battery. Remove the passenger side kick panel and then loosen the 10 MM hex bolt that secures the computer wiring harness connector to the computer. Pull the wiring harness connector down so that it disconnects from the computer.

Make sure that the TPS & EGR sensors are disconnected while performing the following tests. If you don't disconnect them, you will get incorrect measurements.

A.) TPS sensor: measure the resistance between the TPS green/lt green wire and pin 47. You should see less than 1.5 ohms. More than that indicates a wiring problem. Then measure the resistance between the green/lt green wire on the TPS sensor and ground. You should see greater than 1 Megohm or an infinite open circuit.
Adjust the TPS sensor as follows:
Set the TPS voltage at .5- 1.1 range. Because of the variables involved with the tolerances of both computer and DVM, I would shoot for somewhere between .6 and 1.0 volts. Unless you have a Fluke or other high grade DVM, the second digit past the decimal point on cheap DVM’s is probably fantasy. Since the computer zeros out the TPS voltage every time it powers up, playing with the settings isn't an effective aid to performance or drivability. The main purpose of checking the TPS is to make sure it isn't way out of range and causing problems. Put the safety pins in the Dark Green/Lt green wire and Black/White wire. Make sure the ignition switch is in the Run position but the engine isn't running.

B.) EGR sensor: measure the resistance between the EGR brown/lt green wire and pin 27. You should see less than 1.5 ohms. More than that indicates a wiring problem. Then measure the resistance between the brown /lt green wire on the EGR sensor and ground. You should see greater than 1 Megohm or an infinite open circuit.

C.) If both the above tests pass, then the problem is inside the computer. This is a replace the computer with a known good unit and retest to see if you get the same low voltage readings. If you do, then your DVM may be whacko…

slow347coupe · Mar 24, 2009

i am havin close to the same thing. but car starts everytime when has set for awhile/cold start, but after the car comes up to temp and you shut it down it will not start and im not getting correct reading at the tps. wait awhile / car cools down check tps and i get a 5 volt at orange and .97 at green and car will start! Its driving me nuts!!!! if you find anything out please post what it was and i will do the same for you. the wierd thing is you can start it and drive it for hours with no problems but as soon as you shut it off. it will not start untill it cools down i have tried different tps, tfi, computer, harness, and i already has new o2, and injectors, mass air meter

1965GTFB · Mar 24, 2009

Thanks,
That's the list(saw and printed it from a prior post of yours) that I was starting to read when the crazy thing suddenly had good voltage, shut off the pump and I could start it the first time. I'll assume what you posted here is the same as the one I already printed unless I hear different.
I'll try working the list again and if it starts to work again I'll wait until it reverts back to not working to continue the tests.

Today I turned the key on and let the pump run(TPS voltages were low again) and sure enough after about 4-5 minutes the pump shut off and the voltages were up(green .91-4.65 @ WOT, and orange 4.99). It started right up. While running checked voltage at battery 14+ (12.11 not running). Then moved it to another part of the driveway which took a minute or so and it died and would not restart.

After 2 full restorations, daughter's 66 and oldest son's 68, I need to remind myself that I should have the patience for this. I'll try working through the list again tomorrow(wed.).

1965GTFB · Mar 28, 2009

Jrichker,
Here are the results of all the tests from following your very detailed and very helpful list you posted above, hope I did them right since I got some negitive v readings and I didn't always find an orange/white wire. Thanks again.

2. B.) -1.4v
2.C.) -0-v

3.A.)1.3v
3.B.)1.3v
3.C.)1.3v

4.A.)-1.6v
4.B.)-0-v
4.C.)-1.6v

5. meter on 200 Ohms setting
5.) TPS .9 on Blk/Wht, 1 or no change on Grey/Red & Grey/Wht
EGR .9 on Blk/Wht, 1 or no change on Grey/Red & Blk/Grn
MAP .9 on Blk/Wht, 1 or no change on Grey/Red & Blk/Green

8.A & B meter on 200 for first part and on 2,000K setting for gound test.
8.A.) .9 on pin 47, 1 or no change on ground test.
8.B.) .9 on pin 27, 1 or no change on ground test.

So at this point it looks like it is the computer. Does that sound right to you guys? Don't have easy access to a known good one to test it with. I also disconnected and reconnected the two 10 pin fuel injector harness connecters and they looked ok.

Now with every thing hooked back up it will run the fuel pump but but it just runs and does not after several minutes shut the pump off and the voltages come up to 5 and let it start and run for awhile like it had done a few times.

At this point unless there are any other things to try I think I'll take it to a shop. I'm guessing with the modern electronic equipment they have they will be able to test the computer pretty easily. Gonna kill me to take in, being a DIYer haven't taken a car to a shop in 15+years.

Will bad TPS shut down injectors?

1965GTFB

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Will bad TPS shut down injectors?

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