108 hot start

[pxland]

I know there is some information on the forum about this but a search turned up none of it.

My 73 280 SEL 4.5 starts great when it is cold, but after it warms up, particularly on a warm day, it has problems starting. I let it sit long enough to cool down a little and it fires right up. It's getting new plug wires this month, which I am sure will help, but I thought I had seen on here that this is a pretty standard problem. Are there any fixes?

Also, I replaced my speedo yestarday and had an interesting experience. After much research I knew all about the knurled nut and was ready for a small battle, but could not find it. As it turns out the PO replaced the knurled nut with (the metric equivalent of) a 1/4" nut. It is a good thing he didn't get it more than finger tight or I may have had to drive it back to his house and run it through his garage door. Anywho... after that obstacle everything went as smooth as advertised. Thank you to Mike and Fred for all the info I needed on that job.

Now that I have a speedometer I know at what speed the violent shaking starts!

Thanks for any input.
X.

[Tomguy]

If your 108 shakes violently you have a major problem there - maybe a bad flex disc or very off-balance wheels - get that fixed ASAP! As for your engine problem...

It's usually a sign that your hot idle is too rich. Back off the large air speed screw 1/2 turn (counterclockwise) while your engine is running. You'll probably hear the idle speed increase. If that doesnt help it enough, don't back it out too far, but pull the rubber cover off the right side of the ECU and turn that mixture screw about 3-5 clicks counterclockwise while the engine is running to lean it out some more.

It COULD make it worse if it's too lean, but I doubt it. I've never had mine be hard to start with the idle too lean, it's always when it was too rich. If it speeds up when you turn the ECU screw (not the air speed screw) then it's a sign it definetly was too rich.

[j9fd3s]

ive got the same problem with mine, i'm gonna reseal the intake halves, and the injectors next weekend.

i can start to tell you what its not though. its not the spark plugs, cap rotor, points (although those did help), plug wires, air temp sensor, efi trigger points, the ecu mixture adjstment (although i think i'm gonna go a little leaner, because of toms post).

mine exhibits the following symptoms: it has a miss/stutter at small throttle openings, and high rpm high load. if its turned off with a hot engine i have about a 10 minute grace period to restart other wise it will catch and immediately die, unless the gas pedal is pumped, until the engine gets over 2500ish rpms, then it just runs poorly for 30seconds.

its worse in hot weather, better in cool weather, and its lately getting worse all the way around. going thru 30 years of repair orders, the intakes never been resealed, and neither have 6 of the injectors, everything else has been changed about 3-4 times....

mike

[Tomguy]

Mike: You bring up a good point with the manifold (and injector) seals. Mine never leaked so I dont have firsthand experience with that. But your stumbling issue does sound a bit more serious than what I experienced due to an over-rich hot start (and maybe more serious than "Mr. X.")!

It almost sounds like your cold start valve is engaging and "Sticking" or leaking somehow. Maybe a bad water thermo-time switch or aux air valve, too? If I were you I'd unplug my cold start valve and see if it made any difference before any warm cranking (the way you say you have 10 mins makes it sound like once it thinks the engine is cold, it will turn it on, thus flooding the engine).

[JMela]

On the hot start issue, try this: Upon starting up your already-hot engine, turn the key halfway so that the fuel pump engages. Let it do its thing for 10 or 15 seconds, then try to start. One of the 109 guys on a different board said getting the hot fuel out of the engine and cooler fuel in makes the difference. Let us know if this works for you.

[pxland]

Tom: It sounds like we have the exact same issue. I attributed the stutter and high RPM miss to bad ignition parts, but apparently I am wrong.

Joe: I read the fuel pump post and tried it before I last tried to hot start it. My fuel pump only runs for about three seconds per key cycle and I cycled it several times....no dice.

[Tomguy]

Try pulling the cold start injector plug before you crank it, see if that does any good. It's located by the air speed screw and aux air valve.

[j9fd3s]

Originally Posted by JMela

On the hot start issue, try this: Upon starting up your already-hot engine, turn the key halfway so that the fuel pump engages. Let it do its thing for 10 or 15 seconds, then try to start. One of the 109 guys on a different board said getting the hot fuel out of the engine and cooler fuel in makes the difference. Let us know if this works for you.

that does help, however whatever it is is still there.

[j9fd3s]

Originally Posted by Tomguy

Try pulling the cold start injector plug before you crank it, see if that does any good. It's located by the air speed screw and aux air valve.

i think i tried this already too. one wierd thing is i dont think the cold start injector works all the time cold, and it definately doesnt work if the cars been in the sun

[Tomguy]

For the cold start valve, it is highly dependant upon a properly-working thermo-time switch. According to the DJet manual, the time it is injecting "reaches zero" between 20° and 40° C. This means, with a properly-working switch, if your coolant is as warm as 40°, the cold start valve may still be turned on. If the switch is bad and is in the closed position at coolant temps of say 60°, which is definetly possible with a 30+ y/o switch dependant upon a bimetallic strip, then it will cause hot start issues.

The aux air valve, according to the DJet manual, should be completely closed between 60° and 70° C. If it's still allowing air to flow through it at operating temp, and idle speed was set thusly, then that can be a major part of the problem. Of course, it's more likely that you have a bad thermo-time switch or water temperature sensor, as this would give harder cold starts, not hot ones.