malachilou

Hi this is my first post. I've been reading the forums for a while to help problems and always solved through searching. Not this time.
Truck is a 1994 k1500 5.7 tbi. If I unplug both tps and map. I get 5 volts to both. If I plug in map it still gets 5 volts but tps drops to 1.2 volts. If tps is plugged map unplugged both still get 5 volts. Both sensors are new. Please shed some light on my situation. Keep getting code 22. Tps low voltage.

bigal55

iTrader: (1)

Sure you got the right MAP sensor? Sounds like it is loading down the circuit by drawing too much current. What prompted you to change both the TPS and the MAP sensors? Because of the low voltage problem? Check your wiring and connections from the reference voltage wire at the TPS and MAP sensors all the way back to the ECM, could be a bad connection somewhere. How's the grounds look? Make sure they are clean and tight. HTH!

malachilou

I believe it is pin f14 on the ecm. And the voltage is same as previously stated. I changed tps because of the code. I changed map after I noticed the it had 5v if map was unplugged. I was thinking the map was shorted internally. Any other suggestions?

bigal55

iTrader: (1)

What ecm are you using, the 427? If so, the reference is on E14. The reference voltage for the MAP sensor and the TPS comes from the same place on the ECM so you really can't have different voltages at the MAP and TPS unless you have a bad splice where the reference wire splits to go to the different sensors. When checking the voltage at the TPS and the MAP, are you using the same ground point?

malachilou

I was mistaken the MAP and TPS show 1.4 volt reference when the MAP is plugged in. But both jump back up to 5 volts with MAP unplugged. Same when checking at ECM. What pins are all the ECM grounds so I can make sure they are good? Does both the TPS and MAP ground at the thermostat or just the TPS and the MAP ground to ECM?

bigal55

iTrader: (1)

ALL grounds are grounded to the battery negative, whether the ECM or any sensors, there is no difference (or at least shouldn't be). You need good connections between the frame, engine, body and battery negative terminal, all these points are at the same potential (ground). The ECM is grounded through the wiring harness and those connections need to be clean and secure, check the connectors and the pins to be sure they are clean and fully inserted into the connector. The ground points on the ECM depend on what ECM you have, 427?

bigal55

iTrader: (1)

From what I can see, B3 is sensor ground and A1 and A2 are the ECM grounds. If I am not mistaken, A1/A2 should be connected to B3 as all the grounds should be connected together. HTH!

malachilou

Yes it is the 7427 ECM.

malachilou

A1, A2, B3, B4, all have small fractional resistance to each other and to ground. Less than 0.6

bigal55

iTrader: (1)

Your reference voltage for the sensors is at pins E14 and F14. The best approach would be to connect the TPS and the Map sensors into circuit and with key on, measure the points for reference and ground at the ECM. If you read the 1.4 volts at the ECM, check the ground points at the ECM to be sure nothing is being pulled up. To do this, place your negative lead from your voltmeter on the battery negative terminal and probe the reference points to verify 1.4 volt reading. If 1.4 volts is verified at the reference terminals, check the voltage at the ground terminals. If you show a voltage at the ground terminals as referenced to battery negative, you have a wiring problem. If you show no voltage at the ground terminals, measure from ECM ground to Sensor reference terminals as a second test to verify the ECM is bad if there is only 1.4 volts between ECM ground and sensor reference.

malachilou

Fixed it. I feel like a big d***a**. Map sensor was pinned wrong. A and C in the connector was backwards. It was cracked so I grabbed a weatherpack from work and changed it. Must have been a long day. Month actually, been working 7 days a week. Thanks for all the help though big al. Sorry for wrecking your brain on my screw up.

bigal55

iTrader: (1)

No problem, it is actually interesting to try and figure these "weird" problems out. Just glad I could help and glad you got it resolved!

malachilou

I was just staring at my wiring diagram in my Chilton manual. When I looked at the map I was wondering why they didn't show the pin letters and it hit me. I had changed it. So I looked up the map in the back, found the section. And sure enough when I went compare on the truck backwards. Thanks again.