camaro1185

Quick back story. Last year I had a problem with the car starting then dying, narrowed it down to a bad TPS. Ordered some off brand one from Rock auto, get it installed and cant get the voltage at closed throttle to go past .3 volts (TPS maxed out on the bolts pointing up). Played with it for a while and couldn't get it to work so i installed a TPS I had lying around, got it set and was able to drive the car for the rest of last season and part of this season.

This past sunday after driving around for about 30 mins, I stopped at the gas station to fill up and as im pulling out of the station the car died on me again (note only happens on a hot restart). It now wont run unless my foot is on the gas. Get it towed home, pull the codes, code 22 (tps low voltage) and proceed to order a good ACDELCO TPS from rock auto again. Install it an sure enough cant get past .31v at closed throttle.

Now the issue seems to be that the "arm" on the TPS needs to move quite a distance to reach the .54V min, and when installed on the TB, i have the sensor rotated all the way up and its only getting .31 volts. I took the TPS off and it reads the correct voltage when I move the arm with my finger. Its almost that the "slots" are not wide enough for the adjustment, or coincidence (and I doubt this) the sensors are defective. Is the voltage suppose to move from 0.00V immediately when the arm starts swinging? if so, mine is not. It takes about 1/8" on the old sensor and probably 1/4" of movement on the new one before it starts to show voltage.

bigal55

iTrader: (1)

Yes, the voltage should start rising in a linear fashion immediately from closed to wide open throttle positions. Using an ohm meter, measure the resistance from one leg to the wiper on the TPS (unplugged) and see if the resistance changes smoothly. You may want to check your reference voltage at the TPS while it is plugged in and key on. If anything less than 5 volts you may have a wiring problem such as corroded connections. HTH!

ASE doc

From this point you need to verify reference voltage to the sensor from the ECM. It needs to be right at 5 volts. If not at least 4.9, you have a problem. Also verify 0 volts on the ECM ground at the sensor. Even slight variations on the reference and ground values will affect the signal value. Check battery voltage and be sure that it's fully charged and the connections are good. Try reading TPS signal voltage with the engine running. If it's closer to normal.

The TPS shares the 5 volt reference supply with other sensors. I don't have my service information available right now. Do you have wiring diagrams? If reference voltage is low, look for an issue with another sensor pulling the circuit down. Try unplugging each sensor on the reference circuit and looking for voltage to come back. Check power circuits to the ECM for voltage drop from poor connections. Check ECM grounds also. On older cars wiring is usually the problem.

It doesn't matter what you can make the sensor read off the car. You can make it read anything between 0 volts and reference off the car. It only matters what it reads on the car. Need to figure out why it reads low. Did you sweep test it? What did it read at wide open throttle?

camaro1185

I will check the OHMs.

I do have 5 volts at the wire key on tps unplugged.

I do have 5 volts. Ill look into wiring diagrams and see what it is wired with. IIRC the CTS is one of the sensors.

I checked the voltage with the tps off the car because this is now my 2nd sensor that I could not get it to set minimum voltage. Both of those sensors while off the car did not start reading a voltage until the arm had moved about 1/4" or about 1/8 of the total sweep then voltage climbed steady.

camaro1185

The more I think about it now Im not sure its a TPS issue. It seems to be a hot restart issue. I honestly have no idea, I plan on tonight installing my FP gauge and the old sensor and seeing if it will start. I will then run it to opp pressure and see if It gives me the same no start issue.

The problem is that the no start issue is so intermittent it may be weeks before it shows again.

So I guess the million dollar question is, can the TPS provide a hard start issue? Once It cools the car starts and runs normal is that tps, fuel or ignition? Also once I get it started (when hot) I have to keep my foot on the accelerator and sometimes that keeps the car running sometmes it dies?

camaro1185

I no longer feel its the TPS. I threw the old one back on was able to set it to 0.55 min voltage.

Here is what I have found after lots checking today.

I ohmed the injectors dead cold and got .01 and .02 on the injectors. Primed the car a couple times to check the fuel pressure. It was 42 psi and dropped to about 25 about a half hour later, that’s normal for the car. Started the car, it started and idled perfect let it run for 20-25 minutes to get it to operating temperature. Ohmed the injectors immediately after I turned the car off and all of them were .02. Tried starting it and it stared but the idle was erratic and after 30 or 40 seconds it stalled out. I tried starting it after that and nothing; it just cranked and cranked no start.

I let the car sit for 30 minutes and stared it again. This time it stared as it did after getting hot. It ran idled and I revved it a few times. It revved perfect and had crisp throttle response (didn’t seem like a fuel problem), but again after 30-40 seconds it stalled out.

What I have been noticing is that the needle on the rpms seems to jump up and down (almost like a voltage spike) but the engine rpm doesn’t change. Then after it jumps a few times it stalls out.
I really don’t think its fuel related. When I rev it, it revs excellent.

I have some vids I took ill upload to youtube and post.

camaro1185

mk1431

I had same problem I replaced fuel pump no problem since

camaro1185

Thanks. I seriously doubt its the fuel pump. Its only 4 years old and I have a dedicated gauge on the rail. It was keeping pressure and raised as it was revved!

Rocket-Doc

iTrader: (11)

Ignition module? Sometimes when they get warm they get flaky... Cool off and back to normal.

ASE doc

Injectors read .02 ohms? You are testing them disconnected aren't you? DVOM test lead tips are a little clumsy for testing injectors. It's easy to accidentally touch the tips together. Be sure that's not the issue. The high impedance injectors should read 12-14 ohms cold and go up slightly when hot. Any coil that goes down in resistance with heat is suspect.

As far as TPS voltage goes, I had an early GM in yesterday reading .34 volts TPS signal with no issues. Yeah that's low but ECM didn't care. Factory injectors on these cars(Multecs) are a notorious failure item. Since the issue is prevalent with the engine hot, I would really zero in on the injectors. Some experts will say if they are original, get rid of them anyway. South Bay Injectors offers the Bosch IIIs which are the preferred replacement. You want the 22lb/hr units.

If you suspect the ign. module, look for no spark when it won't start. Also, check for injector pulse. A noid light is easiest for this test.

BTW, it's just as easy to sweep test TPS signal voltage as it is resistance. I use my scan tool with only TPS voltage selected on custom data screen in graphing mode. Labscope is even better. Since GM doesn't offer a known good resistance value for the TPS, resistance is not an industry recognized method for testing this sensor.

camaro1185

Thanks for all the info! I have been working on it but not updating this thread as much as I should. I went through lots of checks most of what you described, noid light injector, re ohming the injectors (was on the 20K scale first time) was getting 15-16 on all when retested. Tested the coil, spark at the plugs etc.

Long story short it ended up being the ICM.

I got it to opp temp yesterday and started it hot about 7-8 times fires right up.

Now i'm dealing with a few things that started after it was fixed.
1. On hot restart it hunts for an idle for about 5-10 seconds.
2. The fan now turns on with key on from dead cold.

Other than that it runs well.

ASE doc

The fan behavior isn't unusual from my experience. I've seen this on the early GM EFIs when the ECM has been reset. Drive it a few times and see if it doesn't correct itself. The idle could be the same thing. Unless the base idle set procedure is performed, it can take a while for the ECM to relearn idle. Good call on the ICM. Have a great wedding!

camaro1185

Yeah, I took it for a drive this past weekend and on initial key on the fan did NOT turn on . It must have been the ECM was re-learning when I did it a couple days earlier.

The drive went well, the car drove as it usually does did a couple hot restarts and it started each time.

Im gonna take it around the neighborhood a few more times before I call it fixed! The good thing is the car is not getting us to the wedding, my fiance wanted at limo for that, however it will be our ride away from the reception. All the car needs to do is drive away, and maybe a big smoky burnout before we get yelled at by the venue

Thanks for the help guys!

ASE doc

and maybe a big smoky burnout before we get yelled at by the venue

Thanks for the help guys![/QUOTE]

Oh yeah!