Timing? Cam? Carb? '86 K10 bogs like nobody's bidness. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Don Gwinn · 03-29-2005, 11:55 AM

Just so everyone knows, I ran a search and came up with nothing, which is the only reason I'm posting a new thread.

I have a 1986 K10 with a 305 and a Quadrajet. I got the truck from my dad, who drove it for many years until he got a '95 with a diesel. Anyway, the thing bogs horribly, and I've done all the simple stuff I know to do--air filter, fuel filter, clean the carb, etc. My next step was going to be to attempt to rebuild the Q-jet and see if I can tune it better.

It bogs from a stop unless you accelerate hard, which seems to help. Recently, I drove it to work 30 miles away and that night (which was very cold) it died twice on the highway on my way home. Both times I was able to restart it, but the second time it stopped me, it took at least ten tries to pull back onto the road. The truck would start, it would run in gear, but when I touched the accelerator it died again. When that stopped happening, the truck was back to normal, although it still bogged.

However, I spoke to dad and he says he had the carb rebuilt professionally a few years ago. This would be, probably, 7-8 years back. Could it really be due for another rebuild? He thinks it's probably a timing issue, possibly to do with the distributor. I believe that's HEI on this model, but I don't really understand timing or how it works. I want to learn, though.

How would I go about diagnosing a timing problem? On my old Ford, I would just turn the distributor slightly to advance or retard and see what happened, but that wasn't electronic.

1. My search did turn up a statement by someone that "305's are notorious for bad cams." Is there a way to diagnose this problem without simply replacing the cam to see what happens? Come to think of it, the idle is a bit "lopey" though not really rough, and as far as I know the cam is stock.

2. Could timing chain stretch cause this problem? If so, can I diagnose that without tearing the engine down to the timing chain?

3. What about the distributor? This truck did have an ignition module fail once before, when dad owned it, but that cause random shutdowns rather than bogging down on acceleration or bad mileage.

4. What would you do first? Obviously I want to start with the simplest, cheapest thing likely to fix the problem and work up from there.

It's time to start hauling mulch, dirt and lumber again as I work on my ancient money pit of a house, so I need to get this truck running right. Thanks!

Don Gwinn · 03-29-2005, 12:28 PM

http://www.autozone.com/servlet/UiBr...ION&PageSync=5

OK, new question. Assuming I replace the module, which of these parts, or both? What is the difference between an "Electronic spark control module" and a "Module--Ignition control?" Or is there one?

The part that was replaced last time was a crescent-shaped circuit board inside the distributor housing, held in with 2 screws. I refer to that as an "ignition module."

I need to dig out the Chilton, but if anybody knows this stuff well enough to give me a clear, simple answer, I'd appreciate it.

Scrubby · 03-29-2005, 02:17 PM

Don,

I'm not sure what is going on, but I can answer some of your questions.

I doubt it is the module. Every time I have heard of one of those going out it causes random shutdowns or times when the truck will not restart.

The HEI timing is adjusted just like your old ford. Loosen the hold down and turn it to advance and retard it.

First, I think I would check the timing. Get a timing light and make sure it is close to where it should be. Also check to make sure the vacuum advance can on the distributor holds a vacuum.

Then, I would look for vacuum leaks. I had the gasket between the carb and the manifold go bad on my '75 and it did some of the same things. Just get it idling and spray some carb cleaner around the manifold, carb base, etc and see if the engine speeds up at any of those places. If it does you have a leak.

After that, I think the problem is going to be fuel. Since it just died on the highway, I would check out the fuel pump. If that is ok, I think I would rebuild the qjet. Maybe the accelerator pump diaphram is dead or something or maybe the float is not set right.

Maybe someone else has some other ideas.

Hoods69BadBowTie · 03-29-2005, 02:53 PM

I would check the timing first.

Don Gwinn · 03-30-2005, 02:18 AM

Will do! Thanks.

Brad_Olson · 03-30-2005, 10:39 AM

Don, you might find these threads useful:

http://67-72chevytrucks.com/vboard/s....php3?t=146930
http://autos.groups.yahoo.com/group/.../message/11431

Apparently the ESC controller can get flaky and since it affects timing it
could be related. Last weekend I de-ESC'd my '86 and it seems to run fine.
Good luck!

Brad

Don Gwinn · 03-30-2005, 12:53 PM

I found that VERY useful, Brad, thanks!

I balked at paying $130 for the ESC module before I had checked timing and such. Now, if timing, coil and module don't fix it, I'll probably just bypass the ESC. This is my old hauler/beater truck for the moment, and I can't pour a lot of money into it.

Don Gwinn · 03-30-2005, 06:32 PM

WHOA! Pulling on various stuff, just poking around today--and the vacuum hose that goes to the air cleaner has a huge hole burned into it! This seems to make some difference by itself.

Brad_Olson · 03-31-2005, 11:33 AM

A large vacuum leak would certainly make a difference. If the engine runs too lean it'll knock and then the ESC would retard the timing in an attempt to fix it, which would probably make the engine even more sluggish (and even a good 305 is no hot ticket to begin with). If you get a new ESC module ($130 is pretty harsh considering a high-output 4-pin module is under $70) be sure you can replace it if it turns out you don't need it. Do you have the factory service manual? It might have a module test procedure.

As another alternative, the other day I got a Jeg's flyer and a new Chevy 4-pin HEI is $94 and that includes a new coil. http://www.jegs.com

Sounds like your '86 is similar to mine - more of a beater than anything. I figure with mine I can work on my welding skills repairing the rusty frame braces this summer...

Brad

piecesparts · 03-31-2005, 03:02 PM

Quadrajet carbs have tendency to wear in the body of the carb where the secondary needles fit through the body of the carburetor. This is seriously bad on the Carter body, since the Rochester had brass inserts in that area. The bogging could be caused by to much gas trying to pour through a hole that should have a defined amount running into the intake. I suggest a quick change to another carb and drive it that way first, then look at a rebuild of the first carb if the problem goes away. If there is deformation in the area of the needles a launch into the trash pile will be needed.

03-29-2005, 11:55 AM	#1
Don Gwinn Registered User Join Date: Mar 2005 Posts: 6	Timing? Cam? Carb? '86 K10 bogs like nobody's bidness. Just so everyone knows, I ran a search and came up with nothing, which is the only reason I'm posting a new thread. I have a 1986 K10 with a 305 and a Quadrajet. I got the truck from my dad, who drove it for many years until he got a '95 with a diesel. Anyway, the thing bogs horribly, and I've done all the simple stuff I know to do--air filter, fuel filter, clean the carb, etc. My next step was going to be to attempt to rebuild the Q-jet and see if I can tune it better. It bogs from a stop unless you accelerate hard, which seems to help. Recently, I drove it to work 30 miles away and that night (which was very cold) it died twice on the highway on my way home. Both times I was able to restart it, but the second time it stopped me, it took at least ten tries to pull back onto the road. The truck would start, it would run in gear, but when I touched the accelerator it died again. When that stopped happening, the truck was back to normal, although it still bogged. However, I spoke to dad and he says he had the carb rebuilt professionally a few years ago. This would be, probably, 7-8 years back. Could it really be due for another rebuild? He thinks it's probably a timing issue, possibly to do with the distributor. I believe that's HEI on this model, but I don't really understand timing or how it works. I want to learn, though. How would I go about diagnosing a timing problem? On my old Ford, I would just turn the distributor slightly to advance or retard and see what happened, but that wasn't electronic. 1. My search did turn up a statement by someone that "305's are notorious for bad cams." Is there a way to diagnose this problem without simply replacing the cam to see what happens? Come to think of it, the idle is a bit "lopey" though not really rough, and as far as I know the cam is stock. 2. Could timing chain stretch cause this problem? If so, can I diagnose that without tearing the engine down to the timing chain? 3. What about the distributor? This truck did have an ignition module fail once before, when dad owned it, but that cause random shutdowns rather than bogging down on acceleration or bad mileage. 4. What would you do first? Obviously I want to start with the simplest, cheapest thing likely to fix the problem and work up from there. It's time to start hauling mulch, dirt and lumber again as I work on my ancient money pit of a house, so I need to get this truck running right. Thanks!

03-29-2005, 02:53 PM	#4
Hoods69BadBowTie Chevys Kick A$$ Join Date: Jan 2005 Location: Zootown, MT Posts: 12,699	I would check the timing first. __________________ HOODS is what I answer too -'79, '77, '88 Pickup Sold, '85 Camaro, '83 T/A, '81,'83,'90 K5 Blazer All Sold -'79 3/4 ton "Big Yellow Bananna" Lifted 4spd. 39.5 TSL Swampers, The money Pit -'86 K5 Blazer Silverado 6.2 4" lift 35"s -'95 Ext. Cab Shorty 4" Tuff Country rolling 35" M/T's -'83 Monte Carlo T-Tops. 126,500 Original Miles -LATER I would rather push a Chevy then drive a ford!!

03-31-2005, 11:33 AM	#9
Brad_Olson Active Member Join Date: Mar 2005 Location: Stoughton, WI Posts: 187	A large vacuum leak would certainly make a difference. If the engine runs too lean it'll knock and then the ESC would retard the timing in an attempt to fix it, which would probably make the engine even more sluggish (and even a good 305 is no hot ticket to begin with). If you get a new ESC module ($130 is pretty harsh considering a high-output 4-pin module is under $70) be sure you can replace it if it turns out you don't need it. Do you have the factory service manual? It might have a module test procedure. As another alternative, the other day I got a Jeg's flyer and a new Chevy 4-pin HEI is $94 and that includes a new coil. http://www.jegs.com Sounds like your '86 is similar to mine - more of a beater than anything. I figure with mine I can work on my welding skills repairing the rusty frame braces this summer... Brad Last edited by Brad_Olson; 03-31-2005 at 11:36 AM.

03-29-2005, 12:28 PM	#2
Don Gwinn Registered User Join Date: Mar 2005 Posts: 6	http://www.autozone.com/servlet/UiBr...ION&PageSync=5 OK, new question. Assuming I replace the module, which of these parts, or both? What is the difference between an "Electronic spark control module" and a "Module--Ignition control?" Or is there one? The part that was replaced last time was a crescent-shaped circuit board inside the distributor housing, held in with 2 screws. I refer to that as an "ignition module." I need to dig out the Chilton, but if anybody knows this stuff well enough to give me a clear, simple answer, I'd appreciate it.

03-29-2005, 02:17 PM	#3
Scrubby Check out GMTrucks.org Join Date: Sep 2003 Location: Boise, Id Posts: 284	Don, I'm not sure what is going on, but I can answer some of your questions. I doubt it is the module. Every time I have heard of one of those going out it causes random shutdowns or times when the truck will not restart. The HEI timing is adjusted just like your old ford. Loosen the hold down and turn it to advance and retard it. First, I think I would check the timing. Get a timing light and make sure it is close to where it should be. Also check to make sure the vacuum advance can on the distributor holds a vacuum. Then, I would look for vacuum leaks. I had the gasket between the carb and the manifold go bad on my '75 and it did some of the same things. Just get it idling and spray some carb cleaner around the manifold, carb base, etc and see if the engine speeds up at any of those places. If it does you have a leak. After that, I think the problem is going to be fuel. Since it just died on the highway, I would check out the fuel pump. If that is ok, I think I would rebuild the qjet. Maybe the accelerator pump diaphram is dead or something or maybe the float is not set right. Maybe someone else has some other ideas.

03-30-2005, 02:18 AM	#5
Don Gwinn Registered User Join Date: Mar 2005 Posts: 6	Will do! Thanks.

03-30-2005, 10:39 AM	#6
Brad_Olson Active Member Join Date: Mar 2005 Location: Stoughton, WI Posts: 187	Don, you might find these threads useful: http://67-72chevytrucks.com/vboard/s....php3?t=146930 http://autos.groups.yahoo.com/group/.../message/11431 Apparently the ESC controller can get flaky and since it affects timing it could be related. Last weekend I de-ESC'd my '86 and it seems to run fine. Good luck! Brad

03-30-2005, 12:53 PM	#7
Don Gwinn Registered User Join Date: Mar 2005 Posts: 6	I found that VERY useful, Brad, thanks! I balked at paying $130 for the ESC module before I had checked timing and such. Now, if timing, coil and module don't fix it, I'll probably just bypass the ESC. This is my old hauler/beater truck for the moment, and I can't pour a lot of money into it.

03-30-2005, 06:32 PM	#8
Don Gwinn Registered User Join Date: Mar 2005 Posts: 6	WHOA! Pulling on various stuff, just poking around today--and the vacuum hose that goes to the air cleaner has a huge hole burned into it! This seems to make some difference by itself.

03-31-2005, 03:02 PM	#10
piecesparts Parts and more parts Join Date: Nov 2003 Location: Lebo, Kansas (middle of nowhere Posts: 6,821	Quadrajet carbs have tendency to wear in the body of the carb where the secondary needles fit through the body of the carburetor. This is seriously bad on the Carter body, since the Rochester had brass inserts in that area. The bogging could be caused by to much gas trying to pour through a hole that should have a defined amount running into the intake. I suggest a quick change to another carb and drive it that way first, then look at a rebuild of the first carb if the problem goes away. If there is deformation in the area of the needles a launch into the trash pile will be needed.



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