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Rough and unable to maintain idle

Started by 200 hp, 26 June 2012, 01:59 AM

200 hp

2 weeks ago, my '74 350SE was parked in good-to-perfect running order outside on the drive. However yesterday upon starting, the engine runs poorly, far from smooth, and I need to keep my foot on the throttle to maintain idle. Otherwise the revs would drop off and the whole thing dies. I suspect an electrical issue. Puffs of black smoke seems to support this. Ignition harness, distributor and cap, these were already replaced 1 year ago. One of the ballast resistors was replaced as well, though I am unable to recall which one. Best described as the one on the left, lower down on the inner right wing.

I suspect either the second, unchanged ballast resistor, or the ignition coil? Then again, I could be thinking entirely the wrong direction.

koan

I'd consider excess fuel to be the issue, not lack of spark, ignition systems basically work or they don't, black smoke suggests a very rich mixture.

'74 350 would be D-Jet I think which is not my area but as a start I'd look at the electrical connection to the manifold pressure sensor, make sure they are clean and tight.

Can't suggest anything more, I'll let someone experienced in D-Jet fault finding take it further.
Boogity, Boogity, Boogity, Amen!

djetronicista

Do check the hose to MAP sensor if cracked or loose/ disconnected will affect running condition.   Only other thing might be is the plug connector to distributor could have corrosion?
73 mbz 450 SE
78 XJ12 (6ltr from 94)
53 Desoto

TestJet

I have the same problem with my 1979 6.9. Really rough idle, no power and it leaves a black residue coming out of the exhaust. I'm in the process of changing the two ballasts. I have changed almost everything else including injectors, wires, fuel pump, you name it. Can you please tell me where the MAP sensor is located on the 6.9.

Thanks
Bert

Bandolero

No MAP sensor on the 6.9 as it is K-Jet.
Your Warm Up Regulator could be suspect.
Russell Bond - (Adelaide, South Australia)
1978 450SEL 6.9 .... #5166 .... 12/78 (Sold.) [url="//www.ezycoat.com.au"]www.ezycoat.com.au[/url]