Hot Start, Rough Idle When Warm & Engine Roughness issue, all related???

[rothsean]

Ok everyone, thanks for your input on my other hot start thread but I have issue that might be related and I want to get some opinions before I just wave the white flag and take it to DMCH.

Today I take my car for dinner, about 30 miles away. It runs fine initially but around mile 20, by the time we get off the highway, while sitting at a traffic light the engine idles rough. It is worse with the air conditioning on, but even when I turn it off it still runs rough. It stays at 800 RPM, then every 4-5 seconds it goes down to about 500 RPM, then quickly back up. Car shakes slightly when this happens. Happens about 15-20 times per minute while idleing once the engine is warmed up.

I park the car a an intermediate stop and when I go to restart it has the issue where I have to crank it about 15 seconds before it will start to turn over. I get it started and go to dinner. It is off for about 1 hour while at dinner. I go to leave from dinner and the car takes some cranking again to get started and almost dies once started but I added some gas and that stabilized it.

Ok, now the new tricky issue (which I had a few weeks ago but I installed the new all-in-one fuel pump so I thought that fixed it, apparently not). Driving home I stopped at AutoZone to get some seafoam because I planned to run that throught the system soon. I left the car idling with my wife in the car. When I get back 5 minutes later the car was idling bad again. The temp got up to around 200 degrees on the guage while there, but the front fan was on. Once we left it seemed fine until I went to accelerate and the car would slightly jerk back and forth a little when I added gas just after shifting to the next gear.

At each stop sign or stop light the idle was rough and I thought that it would die, but it did not. Once accelerating from a stop it would jerk a little when I added gas. I had to add gas slowly. Example, if I shifted into 2nd gear from 1st and stepped on the gas hard then the car would just jerk back and forth a little. It would feel like a cylinder had dropped off or something. This happened with all gears.

I got it home. It died when I pulled into the garage (perfect timing). It restarted no problem though.


Ok, just so you know I have recently installed the following items, they are all new and I assume they work fine:

-New Spark Plugs
-Rebuilt Distributor with new impulse coil.
-New All-in-one fuel pump from DMCH.
-New fuel filter.
-New Fuel Accumulator
-Oil Change
-New Air Filter



Any ideas?

[Bitsyncmaster]

Did the car ever run good?

Have you adjusted the mixture with a dwell meter?

Have you checked fuel pressures?

It could be ignition or fuel related.

[rothsean]

Did the car ever run good?

Have you adjusted the mixture with a dwell meter?

Have you checked fuel pressures?

It could be ignition or fuel related.

It seemed to run good since I had put the new fuel pump in and changed the spark plugs. But now that I ran it long yesterday 30+ miles without a break it was running rough. Usually I would drive it less than 30 miles and it would cool of, like at a restaurant or church or somewhere else.

I cleaned the frequency valve connections last night. I will drive it this morning and see what happens. What is a dwell meter?

[rothsean]

Did the car ever run good?

Have you adjusted the mixture with a dwell meter?

Have you checked fuel pressures?

It could be ignition or fuel related.


Also, I really don't understand why it runs fine for the first 20 miles or so and then starts to idle rough/struggle for power during acceleration...

[Bitsyncmaster]

You set the mixture looking at the dwell meter attached to the frequency valve.

Since it takes a 30 mile drive to show the problem, my guess would be ignition problem. But it's best to verify the fuel system is correct first.

[lazabby]

There may be a vacuum leak. I'm planning to have a tech session in October. The place I'm hoping to have it will have a smoke machine and we can test everyone's cars for leaks.

[rothsean]

There may be a vacuum leak. I'm planning to have a tech session in October. The place I'm hoping to have it will have a smoke machine and we can test everyone's cars for leaks.

So would this switch have anything to do with a rough idle? What does this switch do? My little flapper stays out after I run the engine up and is not touching the little metal rod that goes in and out. Is that what it is supposed to do?1300713006

[Spittybug]

That little switch is what tells your distributor you are at idle (no throttle) and therefore NOT to advance the timing. It works by closing a solenoid that blocks vacuum from reaching the vacuum advance unit on the distributor. Consequently, you are probably sitting at ~33* of advance at idle. That would indeed run poorly. This switch is supposed to be depressed by the plate on the throttle linkage at idle.

[Rich]

That little switch is what tells your distributor you are at idle (no throttle) and therefore NOT to advance the timing. It works by closing a solenoid that blocks vacuum from reaching the vacuum advance unit on the distributor. Consequently, you are probably sitting at ~33* of advance at idle. That would indeed run poorly. This switch is supposed to be depressed by the plate on the throttle linkage at idle.

While there is an idle microswitch in the throttle system which performs the function listed above, the microswitch in the photos isn't that switch. From the photos the switch in question is next to the throttle quadrant/spool, near the thermostat housing, normally beneath the anti-icing recall shield. The idle microswitch is located closer to the throttle plates. Next post describes the switch in the photos.

[Rich]

So would this switch have anything to do with a rough idle? No, it is the Wide Open Throttle switch What does this switch do? It signals the Lambda and the A/C systems that the engine is at wide open throttle, which defeats certain functions in both systems My little flapper stays out after I run the engine up and is not touching the little metal rod that goes in and out. Is that what it is supposed to do? Yes. The "flapper" is just a contact plate and the rod is the switch shaft. Manually open the throttle quadrant/spool - engine off - and you'll observe the normal switch/linkage function.

The switch in the photos has no effect on the problems with your engine.

[rothsean]

Thanks all for the replies!

[rothsean]

There may be a vacuum leak. I'm planning to have a tech session in October. The place I'm hoping to have it will have a smoke machine and we can test everyone's cars for leaks.

Cool, will you be sending out an email about the date/place/time?

Sean

[dmc6960]

One correction, the Full Throttle micro-switch does NOT shut down the AC system. It should, and its something I've wanted to rig up for a long time, but it doesn't.

[Spittybug]

My bad apparently. I confused the full throttle switch with the idle air shutoff. Do make sure that one is engaging however!

[rothsean]

I dropped the car off at DMCH today for a diagnosis. I don't have time to mess with it right now so it is money well spent. I look forward to see what they say.

[kings1527]

I dropped the car off at DMCH today for a diagnosis. I don't have time to mess with it right now so it is money well spent. I look forward to see what they say.

Just curious. How did DMCH remedy the problem?

[David T]

It wouldn't take much to rig up a WOT switch to kill the A/C compressor and the wiring would be easy since they are near each other. Just make sure you get a micro switch that can handle the load or it won't last long. It is even easier on a 5-speed since you already have the room, on automatics they have 2 WOT micros, one to force full enrichment of the Lambda and the other to signal the shift computer to drop down a gear. If you do not want to go through all of the effort to do this all you have to do is move the mode switch to Vent or Off for a moment.
David Teitelbaum

[TTait]

But... (getting anal here)

The pink wire running to the AC compressor splits in the main wiring bay near the fuse box. It routes from the low pressure switch, to a splice that ties to the output from the otterstat, and then on to the compressor out in the engine compartment.

See here:

http://dmctalk.org/showthread.php?40-All-Wiring-Schematics

post #1 schematic #1

If you were to rig up a WOT switch to cut the compressor, the better place to break the circuit would be between the low pressure sensor and the splice, so that triggering the WOT switch would not only turn off the compressor, but also turn off the cooling fans (unless the otterstat was closed). This would not only decrease drag from the compressor, but also lighten the load on the alternator decreasing drag there as well.


I suppose it might also be helpful to rig up a switch that turns off the license plate illumination lamps when you go to full throttle...

[David T]

There are many different ways to do the same thing. You could put a micro on the gas pedal that runs a relay to shut the compressor, radiator and heater fans. You could use one of the existing micros on the motor to run a relay and do all of the functions, it depends on how creative and how much effort you want to put into it. You start to understand some of the benefits to going to computers. Once you have all of your inputs and outputs you can control them any way you want and it is so easy to change things with a couple of keystrokes. Whatever you do just create the documentation once you get it done so you (or a future owner) can figure it out if need be.
David Teitelbaum