72 280SE 4.5 Sputtering again

[Rackne]

I got all the ignition system mods squared away,XR-700,MSD 6-AL,
Accel coil,Accel 8mm S.S. wires, Bosch platinum plugs, and set the timing. Runs like a rocket, I drive 55 miles to a place that can give me an alignment and I detect a slight surging and then a miss as I get to my exit. Down at the merge its sputtering and working hard at dying. I made it to the alignment appointment and begin the long journey home, some hours later. I found a slight seeping leak at the fuel rail on the #2 injector which I took care of and got a slight improvement. Adjusted the timing counter clockwise to the end of the slot and got another slight improvement. The miss is extreme at lower speeds with smoothing taking place as speed increases. Dead injector(s)?

[hill]

Even with a upgraded ignition system I have never had success with platinum plugs on a D-Jet engine. I have tried several different setups on D-jet cars and found the best setup is stock. Ie Bosch solid core wires with rf shields and copper plugs. Changing points is a 5-10 minute job and cheap to do once a year. If you are spinning the motor past 6K and worried about point bounce you can double spring them.

Search this site re: platinum plugs. You'll find that the consensus is that unless your car was equipped with same from the factory, stay with non-platinum (or non-titanium, or whatever the fad precious-metal plug of the week is).

[Rackne]

Interesting...I've had great performance using them on 76 MG Midget, 70 MGBGT, 88 Yugo, 70 Volvo 144S, 89 SAAB 900S,90 Hyundai Excel and a couple of Camaros. Did the research and point given, the plats are comin out, I'm beginning to think that perhaps I've got a sticky exhaust valve due to lack of power, the back fire, and the way it seems to be o.k. after it sits for a few days.

[cth350]

Get somebody with an engine analyser and CO% meter to polish off that tune once you replace the plugs. You're probably running way rich somewhere.

Get a pressure guage and check your system pressure. The system is calibrated to presume a 32psi delivery. Once you shut off the fuel pump, the pressure should stay up.


Be very, very suspicious of vacuum leaks. Steve posted some good troubleshooting rules there a while back. Start by replacing the line to the vacuum sensor, even if it looks "good".

-CTH

[Rackne]

I replaced the plats with champion copper plus plugs, it seems to run stronger but still with a severe miss, enough to rock the engine. It has a steady 10lbs of vacuum at the fitting on the throttle body below the throttle plate, which seems to indicate a vacuum leak rather than a valve problem. The platinum plugs were blackened with a thin coating of carbon after 100 miles. I've searched for leak without success, which vacuum sensor are you refering to? The gulp valve or the EGR?

[cth350]

A 72 motor doesn't have an EGR valve.

Look for a hose from the back of the manifold to a little sensor that looks something like a VW beetle with a hose stuck up its butt. (when you stop laughing, go out and look).

-CTH

[MikeTangas]

You mean this part, the intake manifold vacuum sensor?



Yes, that line can *look* ok, but be full of cracks and leaks. Line runs from the sensor to the left side of the engine.

[Rackne]

I checked the injectors listening through a large screwdriver and found the #2 and #3 to be quieter than the rest. Then disconected the #2 plug wire and #3 plug wire at the cap and found no effect on the idle. Pulled the #2 plug and found it minty fresh with only a trace of oil, while the others have a light coating of soot. The injectors click and spritz when hot wired, so I'm thinking maybe the ground connection. I'd already pulled and cleaned the injector points and they seem to be fine. Maybe the intake valves need adjustment? The compression on these two cylinders is 120lbs ea. and the spark is excellent. O.K. Made a noid light and got no voltage at the injector, anyone know where the ground connections are for the injectors?

[Rackne]

Turned out to be the injector points, after a few adjustments with some needle nose pliers, (not for the faint of heart) my baby is tearing up the road instead of glaring at me from the driveway.
I'll replace the points soon and not worry about them for a few years.
Thanks for all the help- Edward Richardson III