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Old 09-30-2005, 04:18 PM
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5.7 vortec engine management drivin me insane

So i am trying to fix a 96 gmc yukon that a misfire slowly developed into a blown head gasket. Along the way the owner put in ALL new sensors besides a MAF. Now the issue was the truck would run, but barely and intake manifold vacuum was rapidly fluctuating by ~8 in/hg. Cylinders 4 and 6 developed the leak in the head gasket (that was 1500 miles old) and started about a year ago and has been just running worse and worse till it ate the head gasket. This stuff should be cake for me, i install and tune programmable efi - way more complicated than this stuff. I cant figure it out.
So with all new sensors minus the maf i put a new jasper engine in it. So nothing hard here, but the distributor is aftermarket and has no alignment 'arrow' to line up. So i put it to line up with #1 pin on dist. cap with the crank/cam on cylinder #1 compression TDC. I tried to start it, just a bunch of poping. I checked the temp of the exhaust manifolds with my hand and only #3 has any heat develop durring cranking/popping.

I'm about ready to light it on fire. I did have a scantool hooked up to it with the old engine runnin crappy with the blown head gasket and all the mil code was for a random/multiple misfire. Thanks obdII. I needed a scantool to tell me that.

So the new engine won't start. It just pops. It seems to me i'm a cylinder off on spark routing. Only #3 seems to want to fire. I have been over this so many times i lost track. For the hell of it i tried the distributor alignment on the (what i know is the) wrong crank TDC just to try it. It won't even pop or fart or anything this way. Also, with the old motor one bank of cylinders was adding 50% fuel to 'make up for lean condition' But this was the same time as the head gasket stuff.

Anyone have any ideas? Any help is greatly appreciated.

Marv
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Old 09-30-2005, 05:40 PM
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I cant remember off the top of my head where exactly the rotor points to except it should be aimed at the little point with number 8 on it.

One of the cap holddown screws will be pointing at one of the bolts that hold the upper plenum on, the distributor will only fit in place one way correctly. Its the one on right hand side.

I think the rotor should be pointing about 1/2 from other hold down screw cant remember which side of it though.

Maybe this advise wont be any help to you at at all.


96 Vortec V6 in fullsize truck going crazy

Last edited by Greg Latvala; 09-30-2005 at 05:45 PM.
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Old 09-30-2005, 11:04 PM
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Thanks for the link greg. It confirmed my assumption of timing the distributor.
I do have the distributor in right as far as fitting with the intake manifold. I also have the rotor pointing directly at the #1 pin on the distributor cap right after the #1 cylinder's compression stroke - TDC. Thats how any engine should be who's firing order starts with the #1 as far as i can think...
I also tried the cylinder flame thrower on the #1 cyl without any luck (plug out of threads sitting in front of the plug hole, grounded to light off a pop of fire) There is a good amount of raw fuel smell in the exhaust. Fuel pressure is 62 psi at key/pump on. While cranking, fuel pressure drops with intake vacuum 6~8 psi.

There is spark to all cylinders. I pulled plug wires completely off and put them on how they are marked with the firing order on the dist cap and the odd and even banks of cylinders at least 20 times, every time doing the same odd pop. I had another mechanic put the wires on to make sure i wasn't missing something.

The injectors were 'rebuilt' bosch units, strange thing is that with the old motor (w/ blown head gasket) it would skip like crazy and would run the exact same if i had the some of the ign wires unplugged. I get there wouldn't be much change with the leaky cylinders ign wires unplugged (obvious) but there were 2 others that had no effect on the engines running if unplugged on the other side of the motor. All cylinders on the old motor besides the 2 leaky cylinders were 3% leakdown and within 5% compression of eachother - 130 psi if i remember right. The 'new' injectors and sensors were all put in to try to stop the skip by a different mechanic.

Anyone know an easy way to test fire the injectors? I used a 6v lantern battery to see fuel leakdown times injector to injector, but some injectors sprayed a tiny bit, like 1/10 of a psi, most did a 2psi drop (from 60psi,) and some did a little more than 2psi. Anyone know the minimum opening pressure for these? I assume they are 12v injectors so it might explain odd pressure readings, but i didn't feel like cooking injectors.
Basicly I think my problem is one of these: Bad ECM, distributor timing off by at least one position, pinched/grounded/powered wire for a cam or crank sensor, bad injectors, or fuel pressure possibly not up to spec. Is there anything else?

I'll be checking injector pulse with an oscilloscope tomorrow (which i did when the head gasket was toast and all were at least firing.) i will also check crank trigger and cam/dist signals.

I appreciate any ideas, i am out. I love a challenge but this is grey hair growin stuff.
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Old 10-01-2005, 05:50 AM
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Forget what normal is. If you have the rotor pointing to cyl #1 it is definitely not right it will never run like that. If you put a timing light on it and crank it over youll see that the timing is way off.

Reorient rotor to about 1/2" from other holddown screw. I cant remember which side so you have a 50/50 chance of getting it right on first try.



Also if you look at the routing of the wires inside the plastic on cap theres 2 that pass very close together Ive seen some defective ones that would make it spark the wrong cylinder. I doubt thats your problem but its something to keep in mind for future.
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Old 10-01-2005, 12:31 PM
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5.7 vortec

If you smell gas,I'm not sure about the injectors being a problem.When I used that motor in a streetrod I found that the all of the injectors clogged up after not being run for many months. They are a booger to clean out, so I ended up keeping a spare set cleaned and ready to go. Once I started driving it regularly, I never had another problem. Good luck! Bill
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Old 10-02-2005, 08:33 AM
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[QUOTE=Greg Latvala]
"Reorient rotor to about 1/2" from other holddown screw. I cant remember which side so you have a 50/50 chance of getting it right on first try."

Are you talking the hold down screw near the electrical connection or the one more near the intake manifold? I had the rotor pointed at the #1 pin inside the distributor, not the one outside the dist cap.

Today i am drawing 3 chalk lines on the crank pulley (for each cylinders tdc) with the cyls that should fire on the line written next to it. W/ a timing light i should be able to be sure its right, as long as i draw the lines right.

Bill, how did you clean these injectors?

Last edited by marvinmartian; 10-02-2005 at 04:39 PM.
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Old 10-02-2005, 09:17 PM
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So i did the chalk lines w/ cyl #s for each pair of cylinders tdc's on the crank pulley. Each cylinder was firing (flashing the timing light) on their correct lines/#s while cranking.
The new plug wires i put on saturday were jumping sparks out of the plug boots and cross firing from the dumb wire holders and from touching. They haven't even seen heat yet! I pulled the wires out of the holders and the cross firing is about 90% better than it was (it was crossing about 1 in 3 firing events...) I still need to get this better. I have yet to find a good set of plug wires for this engine. Every set have had leaks somewhere. Has anyone found a company that makes good ones for this engine? Magnecor is the only company i use in my stuff, but they have no listing for vortec 5.7's
I did find a wierd ground issue right before i gave up tonight. with the key off from the - on batt to alternator housing my fluke was reading 0.2 ohms. With the key on it was measuring 20 ohms ?!? I cant imagine what it reads while cranking. The ground cable ends were clean and tight. I'll be getting a new ground cable tomorrow.
I drained the gas tank (with the pump) and put fresh gas in just for the hell of it. The gas didn't have a potent smell at all. It was a light vinegar/laquer smell so the injectors are probably mucked up too.

Last edited by marvinmartian; 10-02-2005 at 09:26 PM.
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Old 10-02-2005, 09:26 PM
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injector cleaning

How's the project going? Looking forward to hearing what was causing the problem. I had the injectors cleaned at a local garage- he has a setup that he described as a cleaning solution under high pressure, with a trigger device that cycles the injectors under pressure. He said clogging is a real common problem with that style of injector. Bill
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Old 10-03-2005, 08:05 AM
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Let me know if you would like me to fax you the correct procedure to install the distributor. I think this is where your problem is at.

Steve
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Old 10-03-2005, 08:53 AM
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Put it at TDC compression then time it like the photo in my album.

I should never rely on my memory.
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Old 10-03-2005, 07:09 PM
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I'd like to say this is one of the most helpful forums i've ever been on.
That said, its not runnin yet but i found at least one of the problems.

Thanks for the pic greg. It is exactly where had it. I don't understand why an aftermarket company goes through the trouble to make a distributor but cant put 2 little alignment notches and #s in. fumb duckers.

Also thanks to steve for the offer to fax me the dist. install directons, and thanks to Bill for makin me think to test the injectors.

Well today i fixed the ground problem and tried to start it. It sounded like 1 and very occasionally 2 cylinders were firing but not well. So i decided to do an injector spray down test.
( take the little top wire cap off the ginormous injector plug. Check that one of the pink wires has ~12 volts (with the key on) and poke a test lead into a wire that isn't pink. pinks are the powers and the other colors are the computer pulsed grounds. Put the end of the test wire somewhere where it won't fall and contact ground. Connect a fuel pressure gauge to the schrader valve on the fuel line that feeds the spider head (injector cluster.) turn the key on so the fuel pump pressurizes the lines, and let the pump turn off - Leave the key on. Then tap the test lead to a ground. Dont hold it, tap it quickly. And dont do this if theres gas fumes near you... you should be able to see the fuel pressure drop with each tap. You will see a little spark on the end of the test whire when you tap. If you want to test another just pick another non pink wire to poke and tap. You will have to turn the key off and then back on to get some fuel pressure again. The fuel it sprays out (about a teaspoon) is not enough to fill a cylinder if you do it once but dont repeat the test on the same injector without turning the engine over to clear it out.)
If the fuel pressure doesn't drop while you tap you have a clogged injector.

Well of the 4 i tested only 1 sprayed. I knew i didn't have to test the rest. They are soaking in some new clean gas overnight. Tomorrow they will get some gas mixed with techron fed through the spider head to hopefully clean 'em. I'm doin all of this out of the truck with a fuel pump and a mini fuel tank. Of course i still have to pulse the injectors, I'm workin on a circuit tonight for that.
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Old 10-04-2005, 10:37 PM
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It runs

I soaked the injectors in a glass jar full of gas overnight. I test fired them today, one injector sprayed a bad mist, another sprayed like a squirt gun and the other 6 were plugged SOLID. These injectors were "rebuilt" and had a few thousand miles on them but the truck sat for a couple months.
I got ahold of the old injectors, washed the business ends off in gas and test fired them. The first one shot a cone of gas about 12 feet, didn't expect that, lucky i guess i didn't light anything on fire. The rest i shot into a gas container. They all sprayed decently so i plopped them in.
It took a little to start, it was flooded at first, blew some grey smoke then started purring.

Thanks to everyone who helped me out.
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