So after changing out the Heater Control Valve on my 89' 944 I may have mixed up the plugs or knocked something loose. I installed it without taking the intake manifold off.

There is three plugs that sit near the back of the intake manifold near the HCV I think one is the o2 sensor and the other two are identical plugs which I've gotten mixed up, tried swapping them around and I still got the same problem. Still not sure which plugs into which because they both fit. If someone could guide me on where atleast one of the wires starts on each side of the cable and meets in the middle and plugs in that would be great. These plugs don't to have the original bracket that held them in place.

I go to start the car and all the lights and stuff works but when I turn the key over all I get is a hum noise and no sound from the starter at all not even a click

Please help

 

Another thing I just found out. Was looking at a vacuum diagram unrelated to the no start issue. Seems that I don't have the correct valve coming out of my brake booster. It's the right angle hose plug that goes right into the booster wall. It does not have the correct check valve on it I do not think. A pre 1989 one that doesn't have the nipple for the skinny plastic vacuum line, Definitely missing a vacuum line because there isn't anything plugged into one of the 90 deg elbows near the battery at the firewall. Wondering if this is the reason if my brakes are so soft and that I have to pump them when stopping

 

Those two Identical wires are you Ignition Trigger and speed sensors. They are the same sensor but different locations. (You only need one to make it run), I would imagine when you try to crank it there is no "Tach Bounce" which would indicate the computer is not getting the signal from the sensors(s) … The really crappy thing is that because they are so old they are brittle and will "Open" when messed with... Sounds like that is your issue.. As an aside... Get BOSCH sensors and not any aftermarket, this is one temperamental circuit… There a re a TON of threads on reference sensors....Check your wiring harness on the car as well … There are replacement kits available. Good luck!

 

You need both sensors. Other than that you're right though. There have been a few cases on rennlist of people getting bad aftermarket sensors out of the box.

The harness wires should be marked with labels - they're a bit cryptic but Clark's Garage will tell you which is which. If the sensors and DME are working, the tach should be doing this when you crank:


To test the sensors properly, you really need an oscilloscope, but you can try this test with a multimeter if you don't have a scope:


It's not definitive, but at least if you get nothing you'll know the sensor is probably bad.

Lindsey Racing makes a replacement harness too if you find that is the problem.

 

Thanks for the replies guys, really appreciate the help everyone has to offer.

The plugs do look a bit worn out. The car did start up right away before I started and finished the work on the Thermostat and HCV. I had disconnected the battery and shifted the leads of the cables out of the way and did notice that one of the smaller wires that is connected to the positive lead post was frayed looking; It's red and is about the thickness of an HDMI cable for a TV gauge wise; does anyone know what this wire is?

The thing is I cannot even get the starter to crank at all so I cannot reference the tachometer for a DME problem if I know what I'm saying, please correct me though if I'm wrong

I cannot see any reference markings on the plugs so I'm still unsure which is which. If anybody could lay it out for me for example, one of the wires starts over here, and the other end starts over here and plugs together at the plug support bracket that would help me out a lot, and then I could plug the other one in. I'll end up putting markers on each one too.

 

Ah sorry I missed that it's not even cranking! If everything is hooked up, check for a voltage drop on the battery cables.

 

No problem probably due to my digressing ha

 

It’s likely a problem with either the positive cable from the battery to the starter or, even more likely, the engine ground directly below the heater control valve.

Check that the positive wire has all its outer insulation in place and that the ground wire is firmly attached.

 

Thanks, Ill check those out, I was looking at the starter briefly before checking back online. Just cleaned up the all battery terminal connections with a wire brush. Ill update

 

Solved! It was the positive cable at the starter, took it off cleaned it up with a wire brush went to start the car, She started cranking BUT didn't start, so I swapped the plugs aforementioned and now she starts up. Thanks a lot everyone