Been chasing an odd issue on my 91 tpi 305 formula where at complete random, the tps signal goes wack due to the 5v reference completely dropping out. Sometimes it happens right away on a cold start, sometimes it happens when it starts closed loop at 160f°. I was looking at a diagram for my ecm and it said the v5 tps reference was pin c14 Grey wire. Well, the two larger connectors, one has yellow plastic, one has black plastic. The one with black plastic has no wire in pin c14. But the one in the yellow connector has a purple wire in c14. Figure I'd just try and test it anyway. It's reading .25v to .5 volts going all over the place up and down. Not sure if this is the right wire and it never hit 1v. Anybody got the correct diagram? Both grounds are good on the engine, new tps and connector. If I read the right wire, is my ecm bad? Thanks for any answers!

 

Small black connector a4 is tps 5v ref.

 

thanks, I'll test it again today and if I'm getting drop out at the ecm ill have to grab a new one. But I really don't know if i should get a reman or a used one. I'm worried both could develop the same issue. not sure which one to go with.

 

just tested it. When the issue happens, the v5 reference drops out at the tps, but at the ecm it stays a perfect 5v. I don't know where else to look, the grounds are fine and it is consistently happening when it starts closed loop.

 

How are you measuring the TPS voltage in the first place?

 

I'm measuring the signal wire on the connector with a soft pierce probe. Tested it multiple times and it's dropping out on the tps but not the ecm.

 

Then somewhere between the probing point and the ECM, you have a wiring issue.