Joseph Barrett

Ok so I'm having some problems that I think might be the ECM. TPS stays at .507 volts even when throttle is moved. Have coad 21. When I jump a&b on the OBD1 fans don't kick on but fan works as it should kicks on at temp when running. Also when a&b are jumped the IACs pulse in and out. IACS extend all the way out when it's running but when you open the throttle they stay extended out. I'm thinking with all this that the ECM is bad. What do you guys think

Kevova

I would test tps with a ohm meter. Does engine still have original round connector type coolant and air temperature sensors, if so change to new style. Check sensor ground circuit, no ground will cause ecm to read sensor source voltage all the time. Too early to condemn ECM.

Joseph Barrett

test on TPS showing. 507 volts on my multimeter with no change when I open the throttle yes it still has the old single plug sensors

Kevova

If you ohm A to B at at sensor will reading should change as level is moved. C should be ground. Old style connector had multiple reliability problems. Are you using FSM?

Joseph Barrett

yes did just that and no change in TPS with movement of throttle or TPS adjustment. No manual new to Crossfire engines but have owned and diagnosed over 40 TPI engines just never seen one do all these strange things at one time I don't understand what would cause the fan to not turn on when you jump the A and B terminals on the OBD1 plug and turn the key on but the fans work like they should when the car is running and why wood the IAC sensors pulse in and out all power and grounds to everything is good I have seen TPS is go bad but usually they still change voltage when you move them around it blows my mind that it just stays at the 507 volts no matter where you move it or how

billschroeder5842

Yep, need to dial in your TPS. That sounds like the first point of failure.

Your ECM is pretty bullet proof- really.

For your cross-fire you need to have really good/functioning TPS, coolant sensor, IAC.

Kevova is correct on upgrading to the dual wire sensors. even if it not your specific problem, you will be glad you did.

Joseph Barrett

I'm definitely going to swap over to the square plug connectors instead of the round

Kevova

Have you disconnected TPS and used ohm meter to see if resistance changes as lever is actuated?

Joseph Barrett

I have not disconnected it to see if anything changes I'll give that a try do I want test where the black and blue wire would plug into or the black and gray wire would plug into on the TPS itself

84 4+3

The fans are only controlled by the switch on the head. It isn't supposed to come on when you jump the terminals on the port. That is if I remember correctly and that mine works normal.

Hot Rod Roy

That's normal. The only thing that activates the fan in the '84 is the CTS in the RH head (between cyl 6 & 8), and the pressure switch in the a/c compressor. Period. FSM pg. 8A-149.

The only way you would know that is if you've got the IAC's removed from the throttle bodies. If the engine is running, the ECM would see way too much air, so would extend the IAC pintles in an attempt to decrease the air flow thru the IAC circuits! FSM pg. 6C14-2.

PatternDayTrader

So does the car run ? if your only complaint is a check engine light on, and a code 21, but everything else is fine, then its almost guaranteed not to be the ECM.

383vett

First step would be to check the voltage output of the tps when the throttle opening is changed. Pretty basic. When a lamp doesn't work, you check the bulb first, not the fuse panel.

Hot Rod Roy

Am I correct in assuming that you have run the engine with the IAC's removed from the throttle bodies? If so, there is a special procedure you need to follow before the IAC's can be re-installed, otherwise damage will result to the IAC's, since the pintles have become extended. This is covered in the FSM pg. 6C14-9.

You do have the '84 FSM, don't you?

Joseph Barrett

no I have not ran the car with the IACs out. With jumper in obd1 and key on I can look into the hole in the throttle body and see and here them pulsing in and out and when I start it without the jumper wire in there I can see through the hole that they are all the way out and when I hold the throttle wide open they do not move at all but I know they should not pulse in and out when the OBD1 is jumped

Joseph Barrett

yes it runs but it idles at about 1300 RPMs then drops down to 9 and Hans back and forth from 6 to 9 has hesitation on take off

Joseph Barrett

okay I unplugged and tested it at the TPS itself and yes I got a change when I move the arm but with it plugged up it just stays at at 5 .07 no matter what I do adjusted or move the arm

PatternDayTrader

Key on engine off.
Back probe the wire in the center of the tps connector with your voltmeter. I'm pretty sure its either blue or purple, but I don't have the proper schematic. Back probe means you leave the connector connected, and using a needle or something similar, carefully insert it into the back of the connector, or pierce a tiny hole in the wire and seal it with silicone later. Try to back probe and not pierce the wire. Pierce as a last resort.
What voltage do you have at closed throttle and open throttle ?

Also, are you using a scan tool to tell you what the ecm is reading for tps voltage ? Or how are you doing that exactly.

Joseph Barrett

using a multimeter when I back probe the wires to the tps I get. 5.07volts at idle and no change when throttle is moved

PatternDayTrader

Ok.
Key on engine off. Everything connected as normal.
Using a needle or whatever, back probe the black wire. What is the voltage reading ?