78' Scout II 4 cyl. issues?

I think it was alittle later than easter. My wife has been taking pics of the girls in our blue bonnets every year since they were born. This was 2 years ago, they are so much bigger and badder(is that a word) now! We now have a 4yo girls, a 2yo girl, and a 6mo yo boy! Yes its like a zoo!
 
ihojeff said:
that box is part of the dtm - decel throttle modulator.
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Just to further some info on this part... My 1977 ss Scout II had one of these, and the fail mode on mine was a slow vacuum leak with the dashpot on my 2210 slowly coming on over time. Made for difficult tuning, now that system has been optimized.
 
Any "decel" system is nothing more than a controlled vacuum leak that begins and ends within a certain parameter.

I'm suspecting that this dtm even is not turning off when it should.

I finally found some information in the service manual regarding this device, however, it's not used on every vehicle across the board. Here's the poop:
 

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May explain the erratic behavior. When it diesels out the rpm's are staying up making them a little to high to kill the engine cleanly and when it backfires the rpms are low and thus the fuel is not burned off leading to the backfire? Does this make since, just thinking out loud?
 
wiggins said:
May explain the erratic behavior. When it diesels out the rpm's are staying up making them a little to high to kill the engine cleanly and when it backfires the rpms are low and thus the fuel is not burned off leading to the backfire? Does this make since, just thinking out loud?
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Kinda.

The curb idle speed is way too high when the dtm fails. That means it's going to "run on" after turning off the switch. Most any engine will do that to an extent if the curb idle speed is too great.

Simply eliminate the switch by bypassing and tell us what happens.
 
Will do, it May be a few days, I am not off work for a while now. Weathers bad anyway. But I will let yall know the results. Here is a pic of my unrestored Scout we have been talking about. Just wanted to show it off a bit.
 

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Thanks Jeff! (and everyone)

some knucklehead had just found a vacuum hose lying around and decided that the top of the dsm was the place for it... Nope!!! Leave that alone..

Everything works as it should now!
 
Ok everything has thawed out and I have some results. I finally got to take the Scout out for a decent run since unplugging the top of the dsm vaccum pot. It ran good and killed good. For research purposes I decided to see what it would do when I disconnected the dsm system all together. So I unpluged the vaccum lines and unplugged the wire harness that goes to the ditributor. Took it for a run and it dieseled out a small amout the first run but killed fine on two more runs. Next I will re power time the Scout with the dsm unconnected and see if that makes it perfect. I suspect it will. Probably wont be able to do this until later in the week.
 
Sorry for the delay guys, but the weather is bad agian and will be for a few days and I just dont drive my cars in this type of weather. I will get back to yall though.
 
Ok I finally got to play with the Scout again. Earlier I had disconected the dcm system but hadnt had a chance to retune the thing after doing so. I now have power timed it and drove the Scout all day long. It ran perfect. Pulled it into the barn last night and it seemed like the idle was a bit higher than it had been all day long and sure enough when it killed it the Scout spit a sputtered a liitle. I cranked it right back up, the idle sounded normal and it died normal. So I thought it was fixed but now I am not so sure.
Forgot to mention after I power timed I went to back the Scout out ot take it for a run and the clutch felt stiff. I decided I had better get out and see what was going on and to my disbelief my transmision crossmember had come unbolted and was hanging about 6'' below the frame. So after fixing that I took her for a drive. Gotta love these old scouts! Crazy thing is the 2 nuts were still sitting on top of the bracket that the cross member was bolted to, must have just happened.

Also I would still like to keep this Scout original so if anyone has one of these speed sensors(dsm's) I would be interested, thanks wiggins
 
Do you have a tach connected to the vehicle or a handheld unit you could hook up? Just curious to know what the actual idle speed is at full operating temperature. Another consideration is the throttle return spring. If you've got some stretched out job on there now, it May not be returning your throttle to the fully closed position on a consistent basis.
 
Yes I am setting the idle speed with a hand held actron(?) meter. It is set at 550. I do have a question on this though. The rpm guage has 2 diff readings one for 8 cyl and one for 6 cyl. It has a note that says double the 8 cyl scale for 4 cylinder engines, but that is way way to high. I have been setting it off of the six cyl setting bc that is what sounds correct. So its at 550rpm on the 6 cyl reading. I figured this way I would atleast stay consitent. My return spring is new and the accelerator pedal is smooth and seems to return normally. Good spring stength another words.
 
I've recently had my own experiences with a handheld meter of potentially questionable accuracy. 8x2 is the correct method for determining idle speed on a 4-popper. The readout you are seeing on the 6cyl sweep is meaningless. I imagine there is some mathmatic conversion, but doubling the 8 cyl figure seems easier. Are you sure you have the test leads connected properly?
 
Pretty sure, its just 2 wires. One to the coil(side that feeds the distibutor) and the other is a ground. When I set it at double on the v8 setting that would be at 1100 rpm on the 8 cyl scale, if I am doing this correct? If thats right it sounds like its at 1100 rpms and not 550 rpm's. One thing I was curious about was the fact that this particular 4 cyl is in all actuality 1/2 of a 392 v8, so do you still time it at a 4 cyl setting or could it be the 8?

No had not looked at the fuel pressure

just had a thought, I wonder if I am not letting the Scout get hot enough before I am setting my carb mix and idle speed. I havent been taking it down the road, just letting it sit and idle for awhile until the temp guage is at normal operating temp

sorry for some of my ignorance here guys I am learning a little as we go. I am absolutley not sorry for some of the other ignorances I May post, lol
 
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wiggins said:
pretty sure, its just 2 wires. One to the coil(side that feeds the distibutor) and the other is a ground. When I set it at double on the v8 setting that would be at 1100 rpm on the 8 cyl scale, if I am doing this correct? If thats right it sounds like its at 1100 rpms and not 550 rpm's. One thing I was curious about was the fact that this particular 4 cyl is in all actuality 1/2 of a 392 v8, so do you still time it at a 4 cyl setting or could it be the 8?

No had not looked at the fuel pressure

just had a thought, I wonder if I am not letting the Scout get hot enough before I am setting my carb mix and idle speed. I havent been taking it down the road, just letting it sit and idle for awhile until the temp guage is at normal operating temp
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Ya simply must have a shop tachometer that reads correctly for the engine you are working with. Whatever it takes! I've never seen a hand-held tach that is not correct for any engine as long as it's working correctly, is connected correctly, and "zero'd" correctly (if adjustable).

The correct base idle speed for a 196 of that era is 525>575 rpm.

A "hot" engine means one that is fully operating at normal oil temperature. That means driving for at least 15 minutes at say an ambient temperature of 60*f.

That is why I suggested you totally bypass the dtm system and drive the rig and determine what happens. There are other "things" going on throughout the entire emissions/drivability scenario on any emissions engine, stuff that changes to some degree continuously. You May in fact have other issues happening intermittently also.

The big picture here is..."drivability" in it's entirety. Everything that is part of the emissions program must work correctly in order to keep everything in original condition. And each engine/transmission combo involved on these vehicles after the 1976 model year is a bit different from the previous model year. For someone who wants to keep these rigs totally original, it's simply imperative that you have a service manual to go by. The manual "set" you need is a cts-2313.
 
Good to have you back mayben. The entire dcm system is unhooked. This is what happened once it was unhooked, but I bet the motor is not hot enough when I am making adjustments. I'll readjust everything tomorrow.
My tach is just one I got from sears a while back. It has rpm, dwell, and voltage and is non adjustable. So when my tach says double for a 4cyl(550 rpm) that would be in the 1100rpm range on the 8cyl scale?
 
I haven't been "gone", I just let this stuff play out and then jump back in when it goes a bit off course! I work here, this is my job!

So yes...simply follow the instructions for the instrument! If you have doubt regarding the instrument, simply install it on some other vehicle that uses a distributor and see what you can read.

The instructions you have suggested are certainly within the norm for these types of instrumentation.
 
Just figured you had been busy. I remeber you said your busy season is coming up. I'll get back with you tomorrow
 
Ok with dsm disconected, I took the Scout out for a good drive,motor good and hot and came abck to make my adjustments. The motor being hotter put my idle speed up around 600 rpms so I put them back to 550 rpm. Rechecked timing, adjusted the air mix on the carb and rechecked the rpm's, which were still at 550 rpm. Took it back down the road and came back , killed it, and it caughed a little out of the tailpipe(light backfire). Confused!
 
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