Can't figure out why truck won't start up properly???

[naystcb]

Ok, so I have an earlier post that touched on this subject but I felt it necessary to start a new thread because I have done everything that everyone had suggested to try and remedy the problem but still cannot get my truck to start up and run like it should.

I have a 1971 Cheyenne Longhorn with a 396 that I have installed an HEI on it because I originally thought that I had a distributor problem that was causing loss of power. After installing the HEI I was having problems with the truck not starting right up and idling rough as well as backfiring.

I have since restabbed the distributor and made sure it was on TDC, it is now timed between 10-12 degrees BTDC, I have installed new pre-made 8mm wires, new spark plugs gapped at .045, have already replaced the rotor and cap on the HEI as well as the coil because I thought maybe the ones that were on the HEI I installed were bad. I have also considered the possibility of an intake leak so I pulled intake off and replaced gaskets and inspected for leaks after. I have replaced all vacuum lines. Yesterday I installed a new Edelbrock 1411 750cfm carb with a new fuel filter and fuel lines and gaskets which I have double checked to make sure are sealed properly. I have checked the fuel pump for proper psi and functionality. Shoot, I even changed the belts and a few coolant hoses while I was at it. I have checked the brake booster vacuum hose that goes into the intake. I had the exhaust completely redone from the exhaust manifold to the rear with dual flowmasters....I have changed the oil and filter...I have done just about everything that I can possibly think of that could be a culprit in this problem except for replace the darn PCV valve, I did change the hose though, and I still cannot get the darn truck to fire right up and run as it should.

When I fire up the truck it doesn't start with the high idle that the electric choke should induce to warm up the truck and then kick down, instead when I fire up the truck it will crank over until I give it some gas and then it will run for a second and then sputter out and stall. The only way I can get the truck to run is to fire it up by pumping the gas, and then hold the accelerator down until it warms up but even then I have to have the idle screw set so that the truck will idle at approximately 1200 rpms all the time or it will simply die..even when the truck is warm. On very rare occasions I can turn the idle down to about 1000 rpms but the next time I start the truck up after it has sat for a day or two it will have to be turned back up or it won't stay running. I don't know what the hell is wrong but this is causing me to lose sleep and hair!!!!

If anyone has any suggestions as to what the hell could be wrong....PLEASE HELP!!!!


IT WOULD BE GREATLY APPRECIATED!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[BAGNDRAGIT]

is your motor original? if so have you tested compression? leakdown? also if you havent checked vacuum at idle (when you can get it there) then i would do that. i actually do timing with a light and a vacuum gauge. also when you do the timing make sure you plug (i pinch the line with rubber line locks) the vacuum advance on the distributor. your looking to be around 15-17Hg. also did you check the vac booster hose, or the booster itself? and im sure you checked the pcv right. sorry had to ask. what type of plugs did you put in?

sorry for the barrage of questions, just trying to better understand the symptoms. hope some of this helps.

[naystcb]

I pretty sure it's the original motor, don't really know if it has ever been rebuilt. It seems very healthy. I think it might have an RV cam in it but I'm not really sure and I don't know how to tell if it does or not. It originally came from Colorado and is now with me in California. When I got it it had a solenoid set up that was connected to a switch inside the truck that was used to kick the idle up on the carb for whatever reason. I removed that when I installed the new carb. I don't really have the tools to check the compression, or a vacuum gauge. When you say check the vacuum at idle do you mean testing the vacuum ports on the carb with my finger for suction? If that is what you meant I have plenty of vacuum coming from the full manifold vacuum port on the carb at idle. When I did the timing the first time I did it with the vacuum advance hose plugged but I think I may have forgot to do it the last time I made an adjustment, would it make that much of a difference when I did a minor timing adjustment? I checked the booster hose and replaced it with new hose and new hose clamps but I did not check the booster itself. I used the recommended plugs as called for in the manual and they were the same as the ones that I removed...I forget the number but I know it had 44 in it and they were AC Delco. Oh, and the PCV valve is rattling like crazy! I don't know what to do but it looks like I still have a lot left to check. :-( Also, is it normal for the carb to make a winding sound when revved...it almost sounds like a miniture gear drive is in the carb by the sound it makes...I don't know if that is normal for new carbs with clean jets or what but it just sounds way different.

[VetteVet]

When you installed the HEI distributor did you run the bat wire on it to the same wire as the old coil had. The HEI requires a full 12 volts and should be fed by a new non resistance wire. Most guys run it from the Ign unfused terminal on the fuse panel. The original ignition coil wire was a resistance wire that cut down the volts to the coil to prevent burning it up. Low voltage at the HEI bat terminal will cause some of the symptoms you are having.

[naystcb]

Originally Posted by VetteVet

When you installed the HEI distributor did you run the bat wire on it to the same wire as the old coil had. The HEI requires a full 12 volts and should be fed by a new non resistance wire. Most guys run it from the Ign unfused terminal on the fuse panel. The original ignition coil wire was a resistance wire that cut down the volts to the coil to prevent burning it up. Low voltage at the HEI bat terminal will cause some of the symptoms you are having.

You know someone had asked me this in my old post but I thought they were just asking if I had replaced the wire with a new one...I had no idea that they meant that the wire had to be completely re-routed. What you are suggesting makes a lot of sense and the answer to your question is yes I did run off the same wire as the old coil had. I will try running off of the IGN UNFUSED as you specified tomorrow morning and see if this helps, actually I am praying it helps! Is it possible that I have damaged the HEI by running off the old wire? Thanks for your suggestion...I'm keeping my fingers crossed!

[BAGNDRAGIT]

thanks VetteVet, i meant to ask that question. and if you say your idle is around 1000 im sure theres plenty of vac, im talking at around 700-850 thats where you would hook the gauge up and read your vacuum. and in this situation a simple timing adjustment isint going to break you. its just recommended. if you think the motor is original, you might want to consider a compression test just for peace of mind, they are easy and you can rent the tool from any autoparts store. and heres the way i test the booster. i grab a clean piece of hose and attach it to the plastic connector that goes in to the boooster, put it on and suck on the hose. if holds a vac, your good. best way is a vac gun so you can detect really slow leaks. the pcv rattling probably has something to do with the current problem. i heard it alot and it doesnt seem to affect anything. and the sound im lost on, i would have to hear it, and know exactly where its coming from.. let me know what you find out, and if you can so those little test to eliminate all those items.

[VetteVet]

I don't think you have damaged the distributor since it still fires. The lower input voltage just gives lower output voltage. The danger is high voltage spikes because the module does not like those and they burn out easily.

[MagmaJct]

Are the advances working properly in the distributor? The weights aren't sticking are they?

Low engine vacuum will prevent low idle speed. Pull the PCV valve and plug it with your thumb. What happens engine idle then? I've seen valves that become fully open and stuck fill vacuum even if they pass the "shake test".

[naystcb]

Ok, so I figured out where the winding sound was coming from...apparently it is the power steering pump. I guess after installing the new belt I may have tightened the belt to much and now it whines upon revving. It doesn't screech like a loose belt but makes a whining or winding sound like a gear drive would. Is this bad or good, I have plently of power steering fluid? Also, the PCV valve is still rattling like crazy but seems to be functioning.

NOW FOR THE GOOD NEWS!

I tried relocating the power wire to the HEI by routing it from the IGN UNFUSED slot on the fuse panel and BAM! It seems to have remedied the problem for now! I will retest in a few minutes and see what happens. I really think this may have fixed the problem though. I will update if it starts to act up again.

For now I would like to thank all of you for your great help and awesome suggestions! You have all made my life a lot less frustrating!

[hatred]

Is there a link or write-up about this wire replacement..?

[naystcb]

Originally Posted by VetteVet

When you installed the HEI distributor did you run the bat wire on it to the same wire as the old coil had. The HEI requires a full 12 volts and should be fed by a new non resistance wire. Most guys run it from the Ign unfused terminal on the fuse panel. The original ignition coil wire was a resistance wire that cut down the volts to the coil to prevent burning it up. Low voltage at the HEI bat terminal will cause some of the symptoms you are having.

@Hatred here is the post that I received from VetteVet about the wiring issue.

[PanelDeland]

Check the truck FAQ's for a write up.The one by member "shifty" is for 6 cyl but the procedure is the same.He gives part #'s and all for a really clean install of the new power wire..
There are others there also.

[CC69Rat]

I need to read better. Thought you hadn't fix it yet. Excuse the edit.

Glad you got it working man!

[VetteVet]

I'll make it easy for you.

http://67-72chevytrucks.com/vboard/s...d.php?t=148346

[hatred]

BUMP.... My truck hasn't been wanting to start and I eventually changed the plugs as they got fouled out by the constant starting. Got it running and it would run for a few minutes then stop. The last time it died I wasn't beside it and my dad said he smelled something burning, come to find out it was the wiring that runs along the channel was smoldering. Went to the parts store and bought some more wire, looks like I'll be making me a new harness. Anyone else had this happen? Also on the firewall seems to be a relay that only had one wire going to it and it has 2 prongs on it. What is this for?

Thanks,


Tony

[domeier]

I'm not a big fan of the wire channel over the firewall. I had rotten wiring in mine from water collecting in it. I got rid of it and ran the new wires in sheathing. The two prong connecter on your firewall sounds like it was maybe the hookup for electric trailer brakes?