84 4+3

I'd be willing to bet if you throw a new tps in that'll fix her up.

KDMatt

Picking one up in a couple of hours. Fingers crossed!!

KDMatt

No dice lads.

New TPS is giving me the exact same readings as the old one. 4.6 volts at "idle" ... then approaches 0 volts at WOT.

I tried manually holding the TPS at the "WOT" position, so that it would read the correct idle voltage, and the car still wouldn't start... granted, it gave me a few extra kicks, but still no go.

What am I missing?

C5 Diag

KDMatt

Fuel is the operative problem.

However I think I've found the bigger culprit.

The GROUND wire that's shared between the TPS and CTS is showing a positive 12v signal instead of continuity to ground... but it also shows continuity back to the ECM ground. What the heck is happening??

84 4+3

Is the ground that bolts to the intake broken off? There should be no possible way for you to have the voltage running backwards on the tps. Something is shorted somewhere. Your opening of the tps and going to zero means that your ground reference is positive. The 4 volts your reading with it closed are a voltage drop caused by the potentiometer. At least that is my theory.

Has it ever run with the 350?

KDMatt

In answer to your question, no, this configuration has not run.

I put everything together last fall/winter and ran out of time to really dig in and troubleshoot before it got cold and snowy. Working on a project car when it's below zero is no fun, no matter how good my heater is.

I checked my intake and block grounds, and those all have continuity to the negative terminal on the battery. I'm wondering if there's a pinched wired somewhere in the harness that's transferring some positive current over to the ground for the CTS and TPS/MAP.

I'm going to have to check voltages at all the terminals going to the ECU now, to see to make sure this short is isolated to this one circuit, or to see if it's present elsewhere.

If it's just present in this one circuit, I could probably bypass it and tie the CTS and TPS circuit to a new ground and see what happens.

84 4+3

You happen to replace the coolant sensor? If it is the knock sensor like one it could be shorted in the plug.

64Scout

You say you have 12 volts on the ground wire? You put the positive lead on the ground wire and the other lead where? I would try touching the black lead to engine, ecm, chassis, and battery. If one of those reads zero volts, it's not grounded and the likely issue.

KDMatt

Thanks again for the replies

@ 84 4+3 -- I did not change the coolant sensor, I will check the circuit with it disconnected. I didn't realize those things could potentially cause a short!

@64Scout -- I put the positive lead on the ground wire for the TPS, and touched the black lead to the ground connection on the manifold, and it read 12 volts. As far as I'm aware this *should* read 0 volts - i.e. it should have continuity but no current, since it should all be grounded.

My next step (when I can get back to it) is I'm going to look at all of the connections at the ECU and make sure that all of the other ground connections there are actually grounded and not shorted, to see if I can isolate where the rogue current is.

As I started undoing all of the plastic loom stuff around the wiring, so I can see where things are going a little bit, and I found a few circuits that had been insulated with duct tape, which is never a great sign. Makes me think someone's dug into this before.

Thanks for hanging in there with me guys.

64Scout

12 volts at the sensor doesn't sound right to me. My experience is with throttle body engines, and iirc those were 5 volt sensors. I'm going to dig around and see what I can find.

KDMatt

I just want to clarify that the actual reading on the sensor is in the neighborhood of 5 volts -- the sensor is just operating in reverse because the polarity on the circuit has been reversed -- i.e. the ground signal going to it has a positive 12v charge instead of a negative 12v charge... which is what I'm trying to sort out.

64Scout

Are you sure you have the right wire to ground? I mean, there are three wires, one is constant voltage supied by the ecm, one is ground to ecm, and the third is the signal that varies with throttle position. Looking at a diagram online the ground is grey, supply is black, signal is dark blue. The black wire also feeds the MAP and temp sensors. As far as me saying they are 5volt sensors, that could be bad memory or could have changed in the years between 84 and 96.

I still think that even with a bad tps it would start and run and the problem is elsewhere, perhaps the wire that tells the ecm that you are starting the engine.

KDMatt

The colors might be different on the T/A, but what I have on the TPS is Black, Blue, and Gray

Gray runs to the MAP and then back into the ECU. Black connects to the CTS, and then back to the ECU. Both the ports that gray and black circle back to on the ECU are labeled "ECU Ground" in my service manual IIRC. I don't have it in front of me at the office.

So as far as I'm aware, both the black and gray wires off of the TPS should be grounded. Blue is the "supply" side IIRC, and the ECU uses the resistance between the respective ground port (port 11) on the black connector, and the supply port (port 5) ... to determine the TPS value ... (port 4 is CTS) ... (also on the black connector)

The ECU for the '82 Crossfire T/A and '82 Crossfire 'vette are the same, so if you're looking at a FSM we should be seeing the same thing.

... and what I'm thinking is that if the polarity on some or all of the ECU's ground ports are wonky, that would explain why the car doesn't want to run.

64Scout

Both the gray and black should not be grounded, just one or the other. One is 5volt reference, the other is the return/ground. The third wire is the signal. I've been looking at http://www.pcfred.com/Vettetip/ECM%20troublecodes.htm among others. See here, C452 #11 is the 5v return. C452 #5 is the sensor/signal wire. C451 #11 is the 5v reference. The ecm monitors the difference between the sensor and the reference wires. The ground should always read zero. Without the ground wire the sensor wire becomes the ground and the ecm just sees 0 volts. IMHO you should not be seeing 12 volts anywhere in that circuit.

64Scout

Just for ***** and giggles, try unplugging the CTS and then check for voltage on the ground. I'm willing to bet it changes, and you have a broken wire in that ground circuit.

Hot Rod Roy

Your wire colors are the same in my '84 CFI, but your description is wrong. Blu (B) is the "sense" wire. Gry (C) is the +5 v. reference, which also connects to the MAP. Blk (A) is ECM ground, which also connects to the CTS.

You may be aware that a disconnected ground wire may read as 12 v. because some device on that ground circuit is connected to 12 v. and that device "leaks" the 12 v. to the ground wire. That only indicates a bad ground, not a connection to 12 v.

My '84 FSM shows a rather unusual ground path for the TPS pin A (blk). The TPS, the Coolant Temp Sensor (CTS), and the Engine Time Sensor get ground thru the shield for the Electronic Spark Timing (EST) cable. This shield is connected to the ECM pin 11 (Circuit #452). You should have continuity from your TPS pin A to your ECM pin C452-11. This ground circuit is NOT connected to any other ground screw.

Hot Rod Roy

If you are finding continuity from your TPS pin A (Blk) to your ECM pin C452-11, you have a problem in your ECM. I find this difficult to believe.

64Scout

Im thinking that the ground/"5v return" is broken somewhere before the ecm, and that's why he's reading 12 volts. If he unplugs the CTS and checks that ground I bet it doesn't read 12v. He should check continuity between his sensors and the ecm plug.

84 4+3