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Old 07-11-2007, 11:53 AM
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4.3L Hesitation Problem...

Hi there everyone! Iím new to the board but Iíve got a problem with a 4.3 thatís driving me nutsÖ

First of all, I always thought of myself as being a verily good mechanic as a kid and as I grew, got tied up with work (as an engineer) and got away from doing any really fun stuff for over 30 years. Anyway, now retired, I thought I would have some fun with our disabled son (who doesnít drive) and have since built him a little show car (Herbie the Love Bug) and now a tow vehicle (a í73 VW bus) to tow the little car around.

Now before you get all upset over the VWís in our lives, there are reasons. However, in regard to this topic, I put a S-10 Chevy Blazer chassis under the bus and mid mounted a 4.3L V6 (í91ish vintage) in the middle to give it enough pulling power. To try to keep it simple and to hopefully make it where I could actually work on the darn thing, I stripped it of all its electronics and replaced them with a cast iron manifold with a small (I think 390 or so) new Holley and solid state HEI.

Weíve been running the bus for a number of months now and just about a week or so ago, it started to idle a little rough. At first I thought it was just the wifeís driving, but soon found it to be worse than she described. It started off as a slight roughness and then finally went into a full blown miss. I had started off with brand new AC Delco plugs when we first got the ďBeastĒ running and found that 2 out of 6 plugs were not fully firing but after replacing them, everything was running pretty smooth. So anyways, I figured that maybe another plug had gone south. So I replaced all of them only to find a spark plug wire had laid too close to the manifold and burned through causing it to of course arc. So I replaced the wire. But now, instead of just having a solid miss, I now have a hesitation while accelerating. So I took out all the new plugs and replace them with the AC which were working and still, the same thingÖ

Ok, now to get to the nitty gritty.

Iíve pretty much ruled out the wires. They are new and even the one that I replaced with an used one, I replace a second time just to make sure. I donít have any fancy test gear left from the Ď70ís and I refuse to stick a test light through the plug wires, but when I pull them one by one, you can tell all cylinders are firing.

The plugs arenít the problem because Iíve now used to sets with the same results.

Iíve rechecked the Holleyís (which was working fine before the burned through wire) float level, injectors, etc., again to no avail.

Iíve checked the few vacuum lines that are left on the engine and I did find the vacuum advance tube coming out of the carb to be loose but after tightening it, the same result.

Iíve checked the distributor cap and see no signís of arcing. It is new along with the distributor.

The vacuum advance hose seems to have plenty of vacuum but I have not used a vacuum gauge on the engine since I really donít own one and due to money issues havenít bought one yet. I guess Iím just old school and stubborn since I never owned one as a kid and turned up everything from my L88 í67 Camaro to just about anything else that was on the road back then without ever using one. Iím told that this is a necessity tool now a days and I guess I could always try to borrow one if neededÖ

Manifold leak? I guess anything is possible, but it is funny that I drove the vehicle the day the wire finally burned through and it ran pretty smooth, i.e., it did not have the hesitation. I also drove it home after the wire burned through for about 25 miles. I canít believe this would have damaged a cylinder, etc., but would appreciate your comments.

Bottom line, I thought I could fix anything that didnít have todayís computerized ignition systems, etc., but Iím really starting to wonder. I really could use some good advise from some of you who have lived with conventional carburetors, etc., on Chevy engines. Where would you turn next? Buying a vacuum gauge, checking the fuel pressure (yes, Iím running a new electric fuel pump with new filters), or what???

Desperate in FloridaÖ

drluv.
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Old 07-11-2007, 12:12 PM
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If you don't have a multi-meter, borrow one from next door and verify 12v on the feed wire that attaches to the HEI. Let the motor idle for a while before checking. I'm thinking you may be using the wire from the VW switch and it may be a ballast wire that reduces voltage to 6v when it heats up. Easy things first.
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Old 07-11-2007, 01:01 PM
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Good thought... I do use the switch from the VW but I run it to a 30amp relay before it goes to the HEI. I, like you thought about possibly having a voltage breakdown although it was running fine. I was thinking of hooking an external 12V source to the HEI and trying it (I might have to do this tomorrow). I haven't checked the voltage at the HEI yet but I will definitely do so right now.

Also, I don't want to sound cheap but after spending every dime we had to try and get the beast running and living on a very fixed income, I just didn't want to put out another 64-80 bucks for a vacuum gauge. However, I just remembered an old vacuum pump I had hidden away which did have a gauge on it. I hooked it directly to the tee going into the base of the manifold and it's reading between 15-16 in Hg at idle, falls off to around 5 or less when you first hit the accelerator and then goes right back up to around 20. Now this is an old engine, not rebuilt, and by what I can remember, that sounded pretty good. However, I'm not sure about it falling off when you first accelerate. Comments please...

I also pulled the vacuum advance line off and checked it. At idle it is practically zero and when you hold it at a steady 2000 or so rpm it goes right up to 15-20. I also put a vacuum on the line to the HEI to make sure the advance was working properly. Actually I just blew air through a tee fitting to generate a vacuum but the advance pulled all the way forward just like it should have.

Later and thanks,

Drluv
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Old 07-11-2007, 02:09 PM
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Update 4:00 EST...

Checked the voltage to the HEI and it seems to be holding between 13.5 - 14 bolts when running. Still want to try a seperate battery source...

Pulled the timing light out again and it's set right at 8 degrees before TDC. I don't know what this engine calls for since I can't find the timing info listed in any book (you have to have the electronic stickers that came on the vehicle), but I have tried advancing it more and less with no results...

For you guys who have been playing with Holleys, I use to remember having problems with them back in the late 60's but and use to rebuild them as well, but I can't remember exactly what types of problems I use to have. I know once on the big block I went through 3 or 4 new ones before I found one that worked well. I pulled the front float bowl off today and checked the float, for dirt, etc., before reassembling it and reseting the float level an checking the throutle jet response. Everything look just like new (good thing since it is). Again, it was working fine.

Symtoms once again, low end hesitation (almost like a miss) which is causing it to surge (like it's trying to run on everything but it isn't). At idle it's pretty smooth and if you just rev it up while sitting, it responds well. Could it be carburation???

drluv
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Old 07-11-2007, 02:43 PM
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It sounds to me like it`s running lean, either from a vaccum leak or not enough fuel from the accelerator pump, pull and plug check the color, if it`s white it`s lean. Here`s a simple test you can do, with the engine off, remove the breather, shine a light in the carbs primary side, move the throttle, you should see 2 streams of fuel come out of near the top of the carb, and they should spray the instant you move the throttle. If not then the carbs accerator pump is likely ruptured. If that checks out okay, check the intake botls for tightness, if you find them loose retorque them to proper specs, then test drive the vehicle, if the problem is still there, remove the carb and look in the plenum, if you see oil, you have a vaccum leak at the intake manifold gaskets. I dunno where you priced a vacuum gauge at, but I think I paid $20 for mine at the local parts store. Next thing you can check is use your vacuum pump to assure the vaccum advance is holding a vacuum, also check the mechanical advance under the rotor to make sure it`s advancing also. DO you have the vacuum advance connected to a direct vacuum source? if not it should be. You can also use carb cleaner to check for vacuum leaks around the carbs base gaskets. Here is a link that will help you to maybe find answers using a vacuum gauge:
http://www.therangerstation.com/Maga...acuumLeaks.htm
Just scroll down and look at the charts on this page, it will give you much info. While you have the cap off, check both the cap and rotor, make sure there both in good condition with no moisture.
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Old 07-11-2007, 06:42 PM
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Some great ideas above... The plugs seem to be running great. I even took several into the parts house just to ask their opinion and they agreed for an old tired workhorse they do look good. As for vacuum leaks, I will spend more time on that tomorrow. Like I've mentioned, I did check the manifold vacuum and vacuum advance and they both seem to be excellent. I really wonder about the Holley but there is no reason for me to believe it's just gone bad over night . One additional thing I wanted to throw out is that it has been idling rough for a couple of weeks and I assume that was because of the bad wire.

However, I have noticed that our local Walmart where we buy our gas has started using Ethanol and I was wondering on engines even like the stock 4.3 if this can cause problems???

drluv
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