Ok, Engine intermittantly dying, and I'm stumped. SOLVED!

[73k5blazer]

Ok, again I have troubles with this friggin engine! It's the 4.3L V6 in my '86 C10. I built the motor last fall, it now has 8000mi on it. This is a great problem, that has me pissed and intrigued at the same time. More pissed than anything else.
What the truck does now, and this just started 2 weeks ago, I start it runs great. Truck wamrs to operating temperature, and starts cutting out, dumping gas into the exhaust, the thing spits, pops, backfires midly and violently, out the exhaust, does that for 2-3 minutes, trucks runs perfect for the rest of the day, or until it gets cold again.
I have no emmissions, it has a holley 390cfm carb on it, I've had the HEI module checked, I disabled the ESC with disconnecting the sensor, then disconnecting the harness at the distributor and jumping pins a & c so it runs. Still it does it,so its not ESC. Plugs are new, wires are new, plugs are nice light brown color. Could this be a carb problem? Blown power valve? It's either not getting spark, or just way too much gas, but only at the point it reaches operating temp? It's seems to be getting worse too. It started just a couple little pops and whatnot, now it's to the point where I don't think it's going to make it next time. I ran compression and leakdown on all cylinders, 175psi +-3, and 8% leakdown on all of them. So I don't think its and internal engine problem. This is really ticking me off......I'm going to pull it in the garage tommorow and start checking things out, again. Just thought I see if anybody has an opinion on what this is.

 

[diesel4me]

weather??

Choke adjusted properly??--or perhaps ita a hand choke,and is being opened too soon?..


If its worse during foggy or damp weather under 50 degrees,it could be carb icing..my 79 C10's edlebrock runs like that during warmup somtimes and stalls at idle when the weather conditions are favorable for icing..the adapter/spacer I had to use to make it fit the stock Q-jet manifold makes the carb stay ice cold,even long after the motor is well warmed up to operating temparature..

Try adding "Dry Gas".the isopropanol stuff for EFI vehicles..it will prevent the icing,and also rid your tank of any water..if it improves,I'd say the carb is running too "cold",and could use more heat under its base..Ford's had a "hot water" spacer under many of their 2BBL and 4 BBL carbs,and ran crappy without them hooked up..the heater hoses ran to the "spacer" and helped vaporize the fuel..

A few other possibilities are an EGR valve opening when it shouldn't be,due to a defective ported vacuum switch..a bad pick up coil or ignition coil that shorts only at certain temps,or condensation building up in the distributor cap..also if it has an EFE valve (heat riser) and a hot air tube from exhaust to the aircleaner,it will help a lot to prevent carb icing!..--
if yours has an oxogen sensor,it might be when it switches from "open loop" to "closed loop" as the engine warms up its acting up,or sending the ECM erratic sensor readings.

A power valve blown usually causes extremely rich at idle,flooding,and poor power output..backfires can toast one on many Holleys unless they have "backfire protection"...


.

 

[73k5blazer]

It's got an elec. choke, no EGR (edelbrock manifold), no EFE, no oxygen sensor.
Could be icing, but why all of a sudden? Motor ran great the first 8000mi, it was really cold 3-4 weeks ago too, 0 at night 20 during the day. Ran find then. Mabey it's this wet 30-40 degree stuff it doesn't like? I'll try the dry gas to see if it improves. Thanks.

 

[the beast]

If it's dumping gas in the cylinders, I'd tend to say you're loosing spark. Check all your gounds and wiring. I had a similar problem and it was a bad ground.

I have a holley and an Edelbrock Air Gap RPM on my truck. It ices all the time in the winter. Runs crappy, but doesn't cut out.

 

[73k5blazer]

Checked the grounds before. Put a brand new engine ground strap on when I put the motor back in and checked 'em last week to ensure a good connection. The thing I don't get is why only at the point where it reaches operating temperature. It's got to be something basic, the ESC is still disconnected, this engine is totally on it's own no computer or emmision controls.

 

[73k5blazer]

You may be on to something with this icing thing. When I put the holley on, I elminated the heat riser, because the new air cleaner had no provision for one, (nor could I find anything but wide open air cleaners in the aftermarket).
Anyhow, Took it for a drive noon today, temp 32, dewpoint 1, hum 92%, according to this chart, ideal condistions for carb icing. It started doing it after 5minutes of running, I got out, and the base of the carb was really really cold, I think I may have seen frost around it in a few places. The icing thing makes sense too, I was doing a lot of reading on it, and carbs don't usally ice below 25 degrees or above 40-50 degrees. So that would explain why it ran great the first 7500mi when it was still warm out, and why it ran fine when 3 weeks ago when it was 0 at night and 10-20 during the day. Very cold air is dry I guess, so no icing.
So I kept it in the heated garage all afternoon, at 55-60 degrees, with the prediction that it would do it, but not as violently, I took her out just now, it still did it, but much much less and took a little while longer to do it. When it started doing it, I got out and felt the base of the carb, cold, but not as cold as it was this afternoon.
So I think I'll remove the heat insulating spacer, because the manifold was warm, and give it a try. If that doesn't work, I guess old fords w/holleys came with coolant heated spacers for a while inthe 60's and 70's, for the purpose of preventing icing.
It's a mabey at this point,but my best educated guess so far. There's at least of evidence to support it. Still can't understand why it would backfire, but hmm....

 

[73k5blazer]

I removed the spacer, took it for a drive, and it didn't do it. But, it was still a little warm from the drive an hour previous. But I think I would have gotton at least a spit or a hesitation, and all I had was smooth running. The real test will be in the morning, when the engine will be dead cold again, supposed to be same conditions as today, 32-34 temp, and high humidity and dewpoint right around freezing, the ideal conditions for icing.
Icing, boy, I really hope its it. I would have never fathomed that one. Thanks and HAPPY NEW YEAR!!!

 

[Willy-N]

Iceing up can be a problem

I removed the spacer, took it for a drive, and it didn't do it. But, it was still a little warm from the drive an hour previous. But I think I would have gotton at least a spit or a hesitation, and all I had was smooth running. The real test will be in the morning, when the engine will be dead cold again, supposed to be same conditions as today, 32-34 temp, and high humidity and dewpoint right around freezing, the ideal conditions for icing.
Icing, boy, I really hope its it. I would have never fathomed that one. Thanks and HAPPY NEW YEAR!!!

When the temps are in the 32-40 deg range it can be a real problem when the humidity is high. For a test if you can draw some heat off the exsaust manifold and get it into the air cleaner it will help. A good way to test for freeze up is when it happens, shut the engine off for a few mins (about 5) and let the engine heat warm the carb. If it fires right off that probley is your problem. My Modified Baja with Webbers did the same thing all the time in the winter till I ducted in a 4 inch flex pipe off my headers to get warm air on the carb. Never had the problem again. Befor it would just start loosing cylinders till it got down to one and the manifold would freeze closed and inside the carb venturie real bad. It would form Ice all over the outside also. Mark H.

 

[73k5blazer]

It still did it this morning, albiet not nearly as bad. Conditions were same as yesterday, dead center on the "Severe Icing" area on the chart. 92% hum, 32 dewpoint 33 temp.
If I shut it down for 3-4 minutes, then start it up, it doesn't do it for about another 5 minutes of running.
I'm going to try to rig a heat pipe from the exhaust. The basket on the right exhaust manifold is still there, just need to rig something around the holley air cleaner to accept it.
I found one of those old ford holley base plates that plumbs into your heater hose lines on ebay. $10, so far. I might try that too. What's better, heating the base of the carb, or shoving heated air down into it?

 

[beater_k20]

heating the base of the carb would be the better option.

 

[diesel4me]

Icing sucks..

The only good place for icing is on a cake....its a deadly thing to have on a vehicle's carb,or even worse,on an airplane!..our area is noted for this,the Christy "Dry Gas" company originated in my hometown to combat this problem on older cars many years ago..Isopropanol alcohol works better than Methenol does,and removes water better..

As for the backfires,it could be drops of melted ice hitting the spark plug electrodes--or diluting the fuel/vapor mix enough to cause a misfire..

What do you use for an aircleaner??..if its stock,it will have provisions for the heated air intake from the exhaust manifold..I had one of those Edelbrock open foam triangle things on my truck..I ditched it in favor of the stock one the 86 305 came with..I noticed an immediate improvement in drivability,though it still ices up some--if I had that aluminum foil stove pipe hooked up,I'm sure it would be a lot better..

I also have no "heat riser"--its there,but no vacuum hose on it..I havent had the ambition to find out which PVS runs it..if its the one I snapped off with the engine hoist chain while installing the motor,I'm going to be unhappy! ..

The "EFE",or "Heat Riser" valve shuts off the exhaust flow from one bank of cylinders,and sends it thru a passage built into the intake manifold and it heats the base of the carb up,then it exits out the drivers side of the "Y" pipe....some intake gasket sets have "restrictors" that block those passages off to increase the density of the fuel air mix in hot weather..
I never use them....

I find running them here with those restrictors makes for a cold blooded,miserable to drive running motor,with our weather conditions..seems to reduce gas mileage a lot too,when it runs "too cold" as far as fuel mixture..doesn't vaporize well enough,and it runs sooty and rich,loads up and stalls during warmup..many intakes built up carbon and those passages get plugged,and no heat gets to the carb..same results..

I might do some poking around and see if I can hook up my EFE valve--I need to put a 195 thermostat in anyway,and that alone will help some too..

I've never understood how a carb running "cold" can make a motor run so crappy--but I've had several GM's that ran like crap when "lukewarm",running rich,stalling,etc..then run perfectly as soon as the carb got up to temparature..almost like a switch was flipped,it would straighten right out!..and they ran great stone cold too,until they got to about 160 degrees..

I learned adding dry gas eliminated most of it,but restoring the heat riser operation, and using the OEM air cleaner was the real cure..GM used both heated carb bases and the hot air pipe on the aircleaner..around here,you NEED both!--its not just a unessasary piece of "smog crap" to be eliminated..

BTW--extremely cold days never bother my truck either --usually the air is extremely dry on frigid days..no moisture= no ice....

 

[73k5blazer]

Well, I fabbed an air cleaner shroud to fit over the top of the wide-open aftermarket one I got (the OEM cleaner housing didn't fit the holley, so it got ditched). Bought a piece of heat riser tube from the auto store and fitted it to the still existings shroud on the right side manifold, still did it. The base of the carb was no longer frosty or even sweating, it was luke warm, and the heat riser tube was warm, so I no my shroud was working and the problem was not icing.
So I was thinking, WTF is it!?
So I started thinking ignition again.
Out of desperation, I removed my brand new coil I put in when I rebuilt the motor, and put my original 1986 143,000mi coil back in. And , wallah. No more cutting out. Tried it yesterday morning and this morning, drove 130mi today, and not a hiccup.
Ignition coil, who would have guessed? Why only for a short period when it gets warm? It passed the bench tests. Oh well, at least I know what it is now. Maybee I'll order the $40 accell HEI coil. I'm really getting tired of shotty parts from the auto parts stores. I'm pretty carful not to get the ultra cheap crap too, I try to get the best stuff. I stay away from autozone, there's a nice local place, and napa are the only places I'll usally go to.
Thanks for all the suggestions, I think I'll keep my shroud anyway, frost on the carb can't be good. It's still somewhat open on the bottom, so it mixes the heated air with the cool outside air, I'll take it off when it gets warm . again.

 

[mouse]

I had a coil go bad like that once. After the coil got warm, it would slowly die. I disassembled it and found it to only be half filled with the oil it was supposed to have. It took me a while to figure that one out too.

 

[diesel4me]

At least its fixed!..

I'd keep the heated aircleaner anyway..I'm glad you found the trouble..many "new" parts can be defective right out of the box nowadays..especially with the strict quality control in China and Mexico.. ...many coils only act up after they get "hot"...

GM makes 2 types of HEI coils too..make sure your new coil's wires has the same color codes as the old one..they are matched to the pick up coil wires..if you use one that doesn't match,it still runs,but with reduced spark voltage,and could make it run crappy..

I'm going to have to fiddle with my C10 some more as far as the icing goes...today we had perfect weather for carb ice..cool,about 38 degrees,with a light drizzle,and snow melting with lots of fog...I could hardly keep the dam thing running..every time I tried to idle it,it was like I shut the ignition off!..made me nearly crash it,when the power steering and brakes quit when the motor stalls!.

I'm going to put in a 195 degree thermostat (had a 180 in it when I swapped the 305 in it,and I stupidly left it there)..that will help slightly..but I need to get the EFE heat riser hooked up properly,and get one of those foil pipes that send the hot air to the air cleaner..then i MIGHT be able to keep it running without carb icing on days like today..
..either that,or take it off the road for the winter..might have too..I'm broke,and can no longer keep 3 vehicles on the road anymore..I was trying to sell it,(reluctantly)..but nobody will buy it running the way it was today!

I did notice an increase in gas mileage when I got rid of that edelbrock "foam triangle" POS air cleaner..I thought an "open" air cleaner gave better power and mileage,but not on this motor..I used twice the gas today as I usually do..whenever it starts icing up,I can literally SEE th gas gauge dropping..

 

[73k5blazer]

Here's a pic of my makeshift shroud. Air cleaner is K&N 11" dia. 3.5" tall, shroud is 3.5" tall and 13" diameter (so 1" clearance all around) and is open on the bottom. I just took some thin gauge sheet metal, cut out a 13" top plate and a 3.5"x41" long strip and welded them together and put a hole in the side. Doesn't look so great, but no more frost on the base of the carb.

 

[diesel4me]

nice job!...

Nothing too shabby about your modifications!..I'm suprised it works with the bottom open still ,but if there is no frost,it must be getting enough heat to be effective!..

Today I put a 195 degree t-stat in my 79 C10..MUCH better heat now!. --but the EFE valve was a PITA..the rod going to the heat riser from it lost a clip that holds it onto the little "ball stud" thing,and I wasted an hour trying to make a suitable replacement..probably have to get one at a junkyard..

I'm getting the stock air cleaner working right--hooking up the "door" in the snout so it closes and opens properly..still need to buy that aluminum foil hose like yours in the picture..

I tried using a ported vacuum switch that used to run the EGR valve-
(had to remove it to fit the Edelbrock carb on)-- on the EFE valve,but it is not the right setup..I dont have the ported vacuum swicth for the EFE in the thermostat outlet anymore,because the motor was from a G10 van,and it had a goofy angle to it--wouldn't work on my truck!..but I still have the switch,so I'll have to see if it will screw into the intake in place of the EGR one,or get another water outlet that has one in it from the boneyard.. ..more antifreeze spilled!

Just hooking the EFE up direct to manifold vacuum made a big difference..my idle speed increased 200 rpms without touching the carb,after it ran awhile!..and it runs better,but it wasn't foggy or wet today,so I'll have to wait and see how it goes on a crappy day (sunday sounds like carb icing day)..I bet I get a few more MPG with everything hooked up stock and working right..--if it were summer,none of this would be nessasary!

Some of you guys must think I'm nuts,going to such extremes to keep the carb warm..but here its nessasary!..

I know more than one plow truck driver that has a hole sawed in his heater box, the same size as that aluminum foil pipe that comes off the exhaust manifold, and added another one of those foil hoses with a "Y" to the air cleaner ,so the blower motor forces hot air in, and they never have ANY issues with icing,while their friends are buying dry-gas,and having a hard time keeping their trucks running in slushy snowstorms...

All this makes me love my 6.2 Diesel all the more..once you GET it to start,it runs like its warm right away! ..fuel injection is the berries in cold weather!.

 

[73k5blazer]

Yep, alot of people always wonder why so complicated is the factory with the vaccuum goodies, thermostatic valves etc. Some of it is emissions, but drivability under all conditions is a large part of it too. I know lots of people, including myself, who've ripped off all that stuff thinking it will make thier motor run better, and end up wondering why they just can't get it to run right.

 

[diesel4me]

guilty!!

I've done the same.."De-smog" something,only to have it run like crap after,instaed of better..the entire engine was designed to run WITH everything installed and operating!..SOME things can be ditched,but some rob no power or mileage,and should be retained..

I've eleminated the EGR valve on many of my vehicles..mostly because an aftermarket carb wont clear it using the stock manifold..never missed them either,though its loss does make some engines more prone to spark knock,and could damage pistons..

The "EFE" valve,or "heat riser" as the old rigs call it,should always be retained,and the OEM air cleaner,even(or especially!) on an aftermarket carb,since they seem to be more prone to icing,even more so if an adapter or "carb spacer" was added..you can use the open air cleaner all summer,but
not when the weather turns ugly here!

90% of vehicles here with an Edelbrock Performer or Holley carb with an "open" air cleaner will run poorly,stall,load up,and waste gas like crazy during fall,winter,and spring days around here that are cool to cold,and foggy or high humidity...they must have been intended for hot rods and racing applications in arizona or california..they don't run good here when the weather is lousy,unless you keep all the "heat" to the carb like GM intended..they don't call them "cold blodded Chevies" for nothing!~.