Manifold Pressure Sensor (MPS)

Potter · 02-05-2003, 06:58 PM

I offer the obligatory apology for my almost disgusting ignorance.

What symptoms would be present to indicate a failing or faulty Manifold Pressure Sensor?

Why do I ask? I have a '73 2.0 that just does not want to start. I have to crank and crank and crank to get her going.....both hot or cold. It does start, but only after the last gasping moments of battery power are expended. If I jump it with a quick starter it cranks once or twice, and then the next turn of the key and she fires right up. (And I just don't have the stones to always have to ask the dude at the local Shop-n-Rob if I can plug my car in for a second to start it)

New and good battery. Ground to transmission good....even added another one. Battery ground good. New starter. Alternator SEEMS fine. Cleaned FI points. Pulled the fuel injectors and get "good squirt". Good clean sparks from all new plugs. Replaced all the fuel lines.

I am having trouble getting the timing just right (there ain't no mark to gauge by). And I know I need a valve adjustment.

I'm going nuts here. And trying to find anybody in Dayton Ohio who knows anything about the 914 is about as easy as eating ONE Frito while the bag remains open beside you.

Bleyseng · Bleyseng's Garage

When MPS 's go the car runs rich at part load and WOT as it can't sense the vacuum due to a cracked diaphram.
Sounds like a timing issue and maybe the CHT sensor. The 73 2.0 takes a special one w/ the ballast resistor for startup and idle.
There is a timing gauge in the Pelican tech articles use that to install new correct timing marks on the fan. Set the timing to 27' BTDC w/hoses off and plugged. You are getting good spark, right?
Clean all your grounds for the engine/ FI as that might be one of the problems.
Geoff

Bruce Allert · 02-05-2003, 09:31 PM

Ditto to what Geoff said. Do you have a TDC mark? With the gauge that you can print from the Pelican article you can get your 27 BTDC marked on your fan. It's not easy but I got it done by crawling halfway into the engine bay with a good light & mirror. That viewing hole never looked so small!

If you don't have a TDC mark do you know how to find TDC?
bruce

hardflex · 02-05-2003, 11:28 PM

try some starting fluid (ether) in the throttle body. if it fires right off, it's a fuel system problem. if it doesn't , it's a spark/ignition problem.

What does it run like when it is running? that could tell you how bad your timing is off

Potter · 02-06-2003, 06:53 PM

These are great suggestions!! I am going to work through all of them. I'll report back. I'm starting to get a little mojo that maybe I have competing issues. Since it WILL start right up when I put some starter fluid right the gullet, that supports the fuel system theory. But even if I run it for a long time and a long drive, if I turn it off for just a moment, it won't start agian unless I hit it with more fluid, or just keep cranking. I would think that even with a fuel system problem it would start easier in that situation.

You guys gave me some great new leads to follow. Thank you. I can't wait to get out there and start tinkering!!!