Running Rich

7391417 · 09-28-1999, 11:21 AM

Can you all give me some suggestions here? My 73 1.7L is running way to rich, causing misfires and poor idle. All ignition components are new, except for the actual dristributer itself (new insides though). I replaced the cylinder head temp sensor, but that did not help that much, it is not as bad as before but still not good. What could this be? I have also made sure all the hoses are good, I previously cleaned the fuel injection points. What I am down to is thinking that it is the TPS, since the misfires occur in its failure range, and also the pressure sensor, but the pressure sensor is not even two years old, or maybe an injector stuck open? Lastly if I unplug the spark from the #3 cylinder the engine actually runs better as far as misfiring (running it up in the garage not driving it obviously). Thanks for any help.

JP Noonan · 09-29-1999, 08:06 PM

Is the 5th injector (cold start valve) hooked up? They leak a lot of the time. Look at the 914 fans site for the D-jet article. It goes through the whole system. To see if the ijectors are leaking, remove them from the intake but not the fuel line. Place each one in a graduated cylinder, turn the key to build pressure, but do not try to start it. Under pressure thare should be no (or very, very, like one drop an hour, little gas) in the glass cylinder. Let it sit under pressure (if you don't have a FI gauge to see if the system is holding pressure then hook the pump up to run constantly for a few minutes) and see if they leak.

You say the ignition is new. try swaping the old plugs and wires (at least #3) back on. Sometimes new wires are bad. Or use a timing light, and hook it up to each plug wire to see if it is working.

7391417 · 09-30-1999, 09:04 AM

All of the cylinders are running rich. I already checked the fuel injectors, I actually had to replace one. The wires are a second set already so it is fuel injection not ignition. I am going to swap out the pressure sensor with a known good one. I have a feeling that is the problem.

John Rogers · 09-30-1999, 09:57 AM

Check the engine vacuum while running. Our 914 had a hole in the inlet plennum and idle was adjusted low to compensate for higher RPM and this caused vacuum to be down to around 6 to 8 inches at idle and the pressure sensor was trying really hard to compensate. You can put a Mity Vac on the vacuum connection of the pressure sensor and pump up/down to see if engine speed/idle/mixture changes and if it does it might be okay.

oredith · 09-30-1999, 10:04 AM

showing the face of the novice here, how do i check if the engine is running rich or lean? do i have to have an O2 sensor?

Jeff

John Rogers · 09-30-1999, 01:39 PM

The best way is to go to a shop that has an exhaust analyzer and use that. You can get an approximation with plug reading and looking at the exhaust pipe. And finally you can add an O2 sensor as you noted.

Dave at Pelican Parts · Dave at Pelican Parts's Garage

You can tell a few ways. One of the more precise ways is to check the color of the deposits on the spark plugs. If they're black and sooty, that's a rich mixture. If they're white or grey, that's lean. Brown or tan is "right".

For the original poster: Tried a compression check? The last time this happened to me, I dinked with *everything* for a week until I tried adjusting the valves. (Oh, yeah--do that too!) I found that one intake valve was not closing all the way; something was holding it open. That something was the valve seat, which had fallen out of the head. Oops.

The intake charge was getting pushed back into the manifold because the intake valve didn't close. The MPS saw this as more pressure (throttle open) and added more fuel to compensate. Result: Very rich mixture.

I hope that isn't your problem; it's a lot more time and money to fix than anything else. But do read Kjell Nelin's D-jet article; it's great!

--DD