I haven't posted on here in a few years, but I'm again a slant six owner with the recent purchase of an bone-stock '87 D150 (93,000 miles). It's in great cosmetic shape and has run well since May when I bought it. However, with the recent cold weather it has begun to develop a couple problems and I'm not sure if they are related.

First off, it has begun to run erratically - black smoke and choppy idle on cold starts, choppy idle even when warm. Coinciding with this recent development, I've noticed an inconsistent temperature gauge reading - it'll read low (when it should be fully warm) and occasionally rise to normal and then drop again. At first, I thought this may just be a temperature sensor failure, but seeing as it's experience other problems, I'm not so sure... It seems under-powered and straining on the highway as well.

Does this sound like a bad thermostat? Carburetor/choke related? Any other ideas? Like I said, a week ago and for several months prior to that, it ran like a top...

Thanks,
Brendan

Replace both coolant temp sensors- the one for the gauge and the one for the lean burn. The coolant temp is one of the key sensors the computer uses to calculate timing advance and fuel mixture.

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Casually looking for a Clifford hyperpak intake for cheap.

Awesome - thank you. I was unaware that there are two temp. sensors. Where is the lean burn sensor located? One is located near the front of the block, correct? Thanks again.

Here are all of the slant six lean burn sensors and their locations:



Another item to check is the vacuum transducer. It MUST hold a vacuum and it MUST be hooked up to manifold vacuum. It is the most important sensor of all.

If you are going to try and keep the lean-burn system, you really MUST get a factory service manual. There are all sorts of special tests described in the FSM that must be done to troubleshoot the leanburn system.

And replacing the thermostat with a correct temp rated Stant Super Stat probably wouldn't be a bad idea.

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Casually looking for a Clifford hyperpak intake for cheap.

In addition to Reed’s advice, make sure all choke moving parts are able to rotate through their full motion freely without any binding. It is not unusual for a carburetor with some age & miles on it to develop binding, and dirty linkage.

Don’t lube any of these parts, just clean them, if necessary, dress with a fine file or crocus cloth to remove any worn spots that catch & bind.

From a cold start, remove air cleaner and observe action of choke as the engine warms up. This may take several overnight cold starts to catch on to what may be happening.

One more thought, perhaps a thermostat test or replacement should come first, than attention to sensors. Your description of erratic engine temperature readings suggest that the thermostat is sticking. If the thermostat is hanging open it will not allow the engine to fully warm up, which in turn cause sensors via the brain instruct the carburetor to adjust for cold coolant condition. In other words, the choke won’t fully pull off.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Thanks for the detailed information!

Also check your thermostat rating when you replace it. Lean burn slants came with a 195* thermostat.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Ok... Replaced both sensors and the thermostat... Now it's running worse and HOT... Wrong thermostat? The counter guy gave me one, but it doesn't say whether it's 195 degree or not. Thanks.

The rating of the thermostat is usually stamped on the bottom of the pintle of the thermostat (the brass part inside the spring). The spring goes inside the head. Test the thermostat in a pot of water using a candy or meat thermometer. There have been reports of faulty brand new thermostats.

In extreme cases, incorrect timing can make an engine run hot. I think you need to verify the accuracy of the base timing, the integrity of your vacuum hose system, and the accuracy of the vacuum hose hookups. If you want, I can scan the diagnostic section of my 84 Dodge service manual that deals with the lean-burn system.

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Casually looking for a Clifford hyperpak intake for cheap.

Thanks for everyone's help. I adjusted the timing (It was pretty far retarded) and that made a world of difference. Its still reads a bit hot (about a notch above midway) but it stays there... could just be the new temp sensor.

A notch above midway is a touch hot, but acceptable.

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Casually looking for a Clifford hyperpak intake for cheap.

If it is giving you "trouble" then "shoot it"

Rick

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

It is also worthwhile to check if the outer ring of the vibration dampener with the timing marked on it has slipped in relation to the center hub. This happens with age and the timing mark can get pretty far off. My brother's 83 Dodge van had a damper with a timing mark that was a full 8 degrees off.

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Casually looking for a Clifford hyperpak intake for cheap.