Last night I bought a vacuum tested and continued my investigations into why my engine kept cutting out and running rich during my drive home from Columbus.
I checked the MPS, and was worried it might be toast; however I think I am OK. From an initial vacuum of 20 it looses 2 inches in about a minute and 5 in about 5 minutes. I am still waiting for my new CHT sensor but the one in the car reads 2000 OHMS at room tem and about 450 at operating temps. I think these readings are normal.

I then started to dig into the hoses. When my problem started during my drive I initially looked for obvious cracks or hoses loose and did not find any smoking gun, however, last night as I took the air cleaner off, I noticed the two hoses going to the decelerator valve were transposed. Also one of the other lines seemed to have a loose fit ( have a picture )

I also had some questions that perhaps you guys might help me with. This may sound stupid but I looked and looked and did not see a PCV valve, where is it ? Also I have seen a few hose lay outs but none are for a 1975, and I am wondering if it is slightly different. Are there any good hose schematics ? I have the one from PP.

I noticed that the PO appears to have put RTV all around the base of the throttle body, yet it appears to be one solid piece, was he just nuts ? I have enclosed a pic of this.

Lastly I also took the throttle positioner sensor apart, I can see why I was getting a hesitation at 3000 RPM, but as some of you indicated, this should not cause the engine to run rich or cut out.

Here is a pic with the throttle body removed, more RTV everywhere.

Here is what for a moment was the PVC valve, this thing looks abused, and is it even the right one ?

Here is the throttle positioner sensor

Another shot of the TPS

I niticed this hose from the fan shroud goint to the air cleaner, is this correct ? I see some of the layouts have this going to the canester which in my car is out of comission.

I await input and further advice from all of you, and will try to documment this operation with pics, now that I have figured out how to do that.

Thanks in advance.

mps toast?




i've got one and you just have to get jeff to re-calibrate it.

did you test the CHT at its end of the connector, or at the ECU end? it doesn't matter what the CHT says, only what the ECU reads. a broken wire in the harness can affect what the ECU sees - and they sometimes go intermittent before they breal completely... test the sensors at the ECU end of the harness...

I had a similar problem with my 75, the CHT wire from the wiring harness was fraying inside the spade connector. I put a new spade connector problem solved.

QUOTE (dralf @ Jul 6 2005, 05:28 AM)

Here is what for a moment was the PVC valve, this thing looks abused, and is it even the right one ?

This fitting goes on the plenum (the single side plugs in) and the dual outlet connections go to the decel valve (small hose) and the decel valve (larger hose). I would plug this port for now.


The other pic with the large hose coming out of the fan goes to the charcoal canister (air inlet).

All that RTV suggests a crack maybe in the plenum.

order a new TPS as that one is pretty worn

Test the CHT/wiring harness as suggested as an intermittant problem should be a short somewhere.

Check and clean ALL grounds, due to the dirty condition of the motor it could be that. Don't forget the tranny ground strap.

I believe the CHT should read lower than what you see at operating temperature. See: Anders The troubleshooting table is near the bottom and shows the values. High resistance causes rich running.

I had a pair of cylinders that ran rich and a pair that was normal. I cleaned the gunk from the trigger points and burnished the contacts with 1500 grit sandpaper and the problem went away. You might want to check that too.

My TPS looked like yours. I adjusted the arm (kind of pivoted it) to wipe an unworn area to one side of the worn track and it worked fine, the hesitation disappeared. If you try to do this, just make sure to keep the arm parallel to the printed circuit board so that only the "ball" on the end of the arm makes contact with the traces.

Andrew