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Dies at Warm Idle

1

1985K5Blazer305

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Hey guys, I've got a 1985 K5 Blazer 305 LE9 with the HEI/EST distributor. A couple months back I replaced my ignition coil in addition to installing a dual exhaust, and the car ran slightly rough, lean, and hot stalled a couple of times. These stalls went away and she's been running fine (still lean and roughish) for 3 months now. Yesterday driving in cool weather, motor started to bog down and would misfire significantly during acceleration, feeling less like a timing issue and more of an ignition issue. So I swapped my HEI module out, unknowing at the time losing the pin that rested in the distributor cap connecting the ignition coil to the rotor. The car drove as before without bogging at cold start idle, but as soon as the throttle kicked down it would stall. If you held the throttle she'd run just fine, but if you let go of it she'd stall at the lower idle. Removing the cap again, I now realized that the ignition coil had been arcing to the rotor without the pin and the cap had burnt. I replaced the cap (+ a new pin), kept the ignition coil as it appeared fine, but the car would still die as soon as the rpm lowered to warm idle. After confirming the choke was operating correctly, and that there was a spark, I thought it must be my timing. With the vac advance disconnected and the car idling as low as it would go before stalling (by adjusting curb idle screw, between 700-900ish rpms) the timing light showed the timing to be advanced way beyond the markings by the water pump, approx. 30-40* of advance when it should be 8-10*. Retarding the advance would lower the rpm and require the curb idle to be increased until it bottomed out, still nearly 20* of advance. I'm at a loss of ideas as to why all of a sudden this occurred without any change in the carb or timing, please correct any mistakes I may have made and any input is appreciated.
Thanks.
 
you say this is a HEI with EST, Electronic Spark Timing. That says to me you have a computer to control timing. In order to set the timing the computer needs to be disabled. iirc it should look like this and be near the distributor.

WIR420_ezr2.JPG

Just unplug the connector set your timing to spec, and plug back together.
I think you'll find that your timing is very retarded from trying to adjust with EST active.
 
Wes Harden said:
you say this is a HEI with EST, Electronic Spark Timing. That says to me you have a computer to control timing. In order to set the timing the computer needs to be disabled. iirc it should look like this and be near the distributor.

View attachment 470703

Just unplug the connector set your timing to spec, and plug back together.
I think you'll find that your timing is very retarded from trying to adjust with EST active.
Click to expand...
That’s what my 85 K-5 original 305 with the HEI/EST distributor had.
Careful on going too far advanced on timing with that engine - it has 9.5:1 compress but with an old school combustion chamber design and detonation is a very common issue.
But, considering the age of an 85 model it very well might have a replacement motor in it by now so who knows what it may have in it at this point.
 
With that setup, the timing is still controlled by mechanical advance and vacuum advance, so it's also important to unplug the vacuum advance while setting base timing. I thought output from the EST module can only retard from the baseline, so at idle it shouldn't really be doing anything. I looked for some documentation for a couple of minutes, but didn't find anything.
 
Wes Harden said:
you say this is a HEI with EST, Electronic Spark Timing. That says to me you have a computer to control timing. In order to set the timing the computer needs to be disabled. iirc it should look like this and be near the distributor.

View attachment 470703

Just unplug the connector set your timing to spec, and plug back together.
I think you'll find that your timing is very retarded from trying to adjust with EST active.
Click to expand...
Thank you, where would I be disconnecting the computer? The image came in blurry, is it at the ESC under the glovebox, behind the distributor base, or somewhere else? Also, from the description does it sound like a timing issue, or does it sound like a problem with the carb, ignition system, etc.? Thanks again for the help
 
the disconnect should be under the hood near the distributor. Can't say what the problem, until we know the timing is at least close. Know what kind of carb and model will help us solve your drivability issue.
 
Unplugging the connector by the distributor causes the motor to die. It is a black connector, approx. 1” by 3” with a brown, green, yellow, and black wire. Is this the connector that you are referring to? Sorry
 
Wes Harden said:
View attachment 470703

Just unplug the connector set your timing to spec, and plug back together.
I think you'll find that your timing is very retarded from trying to adjust with EST active.
Click to expand...
This doesn't sound right to me. I think that single-wire thing only applies to TBI/ ECM-controlled timing. With the (non-CCC) carb, there is a 4-way weatherpack connector tied to the distributor. That's the connection to the ESC box above the glove box. It's been so long since I had one, but unplugging the connector removes the spark signal.

1985K5Blazer305 said:
Unplugging the connector by the distributor causes the motor to die. It is a black connector, approx. 1” by 3” with a brown, green, yellow, and black wire. Is this the connector that you are referring to? Sorry
Click to expand...
To bypass the ESC box, disconnect that 4-pin weatherpack and install a jumper wire from A to C (on the distributor side). This is just a picture I found of the ESC box side, I'm not suggesting that you cut wires, just to confirm we're talking about the same connector.

1711630338662.png

The '85 diagram isn't showing this on the V8 for some reason, but the V6 seems to be the same. I pasted together the relevant parts:

1711630922256.png

Also see here: https://ck5.com/forums/threads/swapping-a-hei-dist-into-a-ccc-blazer.114122/

Again, having the ESC connected should not affect timing at idle, or any condition except when the knock sensors pick something up, but it's worth trying for troubleshooting/confirmation. The more important thing is to disconnect the vacuum advance and plug the hose to prevent vacuum leak. That will show your base timing. It's never a bad idea to open the distributor and make sure the weights are not stuck, but snapping back to the base position. If they are sticky, you'll get inconsistent timing.
 
This could be right. I am having troubles reconciling a vacuum advance and computer controlled timing. This system I rarely saw.
Since OP can't find the disconnect plug, and described the 4 wire plug. Let go with blue85 explanation.
Need to figure out what changed. When you checked the timing it was way advanced. I think the mechanical advance needs inspection.
 
1985K5Blazer305 said:
the timing light showed the timing to be advanced way beyond the markings by the water pump, approx. 30-40* of advance when it should be 8-10*. Retarding the advance would lower the rpm and require the curb idle to be increased until it bottomed out, still nearly 20* of advance.
Click to expand...
Had you checked the timing back when it was running OK? There's always the chance you have mismatched timing marks. We've discussed this here many times, here's an example: https://ck5.com/forums/threads/balancer-timing-marks-don’t-line-up-with-tdc.349520/#post-4346064. I wouldn't be surprised by 20 degrees at idle, but 40 is suspiciously early.

Wes Harden said:
This could be right. I am having troubles reconciling a vacuum advance and computer controlled timing. This system I rarely saw.
Since OP can't find the disconnect plug, and described the 4 wire plug. Let go with blue85 explanation.
Need to figure out what changed. When you checked the timing it was way advanced. I think the mechanical advance needs inspection.
Click to expand...
The ESC is not computer-controlled timing. I don't know if the controller is all analog or part digital, but the control signals are analog. If knock is detected, the controller inserts a signal which reduces the timing, but that basic timing is all from mechanical and vacuum advance physically phasing the distributor to the pick-up coil. Most of the time, the ESC isn't doing anything and the distributor can be made to run without it (as discussed above).

It was a very common setup in the early-mid 80's, other than California-emissions models. It was on almost all of the 305 trucks (probably because of the high compression heads) and apparently at least some of the 350s. Some of them got badges:

1711645685915.png
 
Update: Unplugging the 4 pin connector would cause the car to die, same situation if only the brown/tan wire was disconnected. Making me think that the base timing is just so off that it can't even run rough without the computer. So I figured I would have to rotate the distributor to various positions and see if one of them would allow it to run without the computer. None of them within the swivel range, before moving the gear, would allow to car to run without the computer. But with the computer and the timing slightly advanced from where it was when the problem started, it would run at the low idle without stalling. And the idle screw could be lowered to close to where it was before. Note: I also ensured the mechanical advance wasn't acting by tying the weights together. Weights untied, I drove it and it didn't bog as much nor did it stall. Where before any sort of acceleration would cause it to bog down, it would only bog under heavy acceleration low in the gear where it is close to stalling. Different from how an engine bogs when stalling however. The engine stills runs rough, not as much, but I can only adjust the timing by ear since the computer has to been connected (vacuum disconnected of course) and I've concluded that my harmonic balancer is not properly aligned. My inclination now is to try adding more advance as that seemed to smooth out the timing. How will the ESC react to excessive advance? Because I felt that as I played with the timing the ESC would be making changes simultaneously. Thanks again
 
General summary of all that is still wrong: After timing and carb adjustments, I still can't get it to run right. The idle remains rough and intense, exhaust either gurgles on the decel or gives a single pop under light throttle let offs, bogs when accelerating but no longer stutters as it did when the HEI module was suspected.

On the carb side of things, with both a vacuum gauge on manifold vacuum and an exterior RPM analyzer, there is no change in either instrument as I play with the a/f mixture screws, it runs the same whether the screws are 3 turns out or 5 (concerning). The idle also walks significantly from 700-1000 rpm randomly, making adjusting the carb rather difficult (bad mechanical advance springs?) Even when holding a constant throttle while driving, rpm will fluctuate over a 300 rpm some odd interval. I was at some point able to hold 20+ on the vacuum gauge so I don't think there is a vacuum leak.

On the timing side of things, I noticed that when I disconnect my vacuum advance there is no change in rpm or roughness, bad canister? I was able to disable the ESC by jumping the black and green wires but at idle the timing on the balancer was still some 60+ BTDC. I could retard the timing by increasing the idle up until about 14 degrees BTDC. But at that point the motor was really struggling and loud metal taps/clicks really concerned me. Before this I roughly checked where TDC was without a dial indicator and was ~16-20 degrees more retarded than the cut groove. Being that the balancer is a 3-bolt, maybe when it wasn't installed correctly which would put it 60 degrees off. Really don't know how to approach this, might just have to take it in but any help is appreciated. Thanks
 
where is your current timing tab fixed ? @2:30 or 12:00 ? Idle air fuel adjustment should make a noticeable difference, but if you idle is fluctuating that much it will be difficult to tell.
While the engine is idling look down the primary venture and see if fuel is dripping from the center nozzle. If fuel is dripping, turn the idle speed screw counter clockwise, lowering idle rpm, until it stops.
I forget which carburetor you have.
Is there vacuum on the vacuum advance hose when you disconnect at idle ?
 
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