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Post by DamnJeep on Apr 22, 2013 20:59:02 GMT -4
Here is another example of what my engine is doing. Andy took this video Sunday. You can clearly hear how the engine is missing, stumbling, back firing and stalling under load. Would not let me rev very high to get any wheel speed. Its a Chevy 305 TBI from a 1989 Sierra Classic now mated to a TH350. Anyone have experience with this? Would a bad EGR valve be a possible culprit? Ignition problem? It has a new fuel pump which is delivering the right pressure (I have a pressure gauge in line). Very frustrating!
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Post by lilmonster on Apr 22, 2013 22:13:10 GMT -4
I know it sounds stupid but whens the last time the temp sensor was changed they are a common problem on the chev throttle body and will cause all kind of issues
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Post by lilmonster on Apr 22, 2013 22:15:18 GMT -4
bin my experience only use dealer sensor they are about $30 I have never had good luck with aftermarket
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Hawkes
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Post by Hawkes on Apr 22, 2013 22:23:41 GMT -4
Did it ever run right? The distributor being out 180 degrees will do that, but maybe you never had it out. Idles but won't open up. Quick way to tell is cold exhaust on one side and hot on the other.
It should run fine with no egr, you could pull it, cover the hole temporarily and plug the vacuum line.
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chevystroker
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Post by chevystroker on Apr 23, 2013 6:55:54 GMT -4
EGR will do that if it is open when it is not supposed to be. My diaphragm cage rusted out, let it stay open. The solenoid valve controlling it could be stuck open, or valve itself could be stuck open from carbon. Did you bump the EGR when you took the engine out? could be bent.
Like Paul said, could pull it and cover the hole to block it.
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KAC
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Post by KAC on Apr 23, 2013 8:39:35 GMT -4
Check pick up gear under rotor button ..they are known for comming loose
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Post by DamnJeep on Apr 23, 2013 8:40:36 GMT -4
Yes I have replaced the temp sensor. I remember someone had told me to do that when I first started having problems. Just can't remember where it came from though! The engine came from a truck that worked fine on the highway. No stumbling or missing problems. I took the engine out complete and have only changed plugs, wires, cap etc and a couple of sensors (when it first started having issues) and have also replaced the throttle body with no significant change. Have not taken out the distributer. If the timing was out 180* would it not start, run like a bag of crap backfiring then refuse to stay running? Last time I had timing off 180 (my old 5.0) it would not stay running at all. Funny thing is when in the shop you can rev the guts out of it and it runs fine. Just not then there is an actual load on the engine while driving hard. So I take it this engine doesn't need the EGR? So I can leave it blocked? Also should mention I put in a better fuel pump which flows properly.
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Post by DamnJeep on Apr 23, 2013 8:41:40 GMT -4
Check pick up gear under rotor button ..they are known for comming loose Will do.
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chevystroker
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NEVER CONFUSE HAVING A CAREER WITH HAVING A LIFE ! ! ! ! ! !
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Post by chevystroker on Apr 23, 2013 13:26:33 GMT -4
Funny thing is when in the shop you can rev the guts out of it and it runs fine. Just not then there is an actual load on the engine while driving hard. So I take it this engine doesn't need the EGR? So I can leave it blocked? Short answer would be no it doesn't really need EGR and yes you could block it off. Longer answer: When the computer activates the EGR, it will expect certain things to change in the engine, and when it doesn't see them, it could trip a trouble code, which probably wouldn't make much difference in your buggy. Other thing is the computer also uses EGR to help stop spark knock. If the engine isn't carboned up inside or prone to spark knock, again, not much difference on your buggy. When my EGR failed, and was leaking by constantly, it acted a bit like you describe; ran okay with no load, but like crap under load. The EGR gases were diluting the mixture and making it misfire.
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Hawkes
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Post by Hawkes on Apr 23, 2013 17:08:51 GMT -4
My 4.3 ran with the distributor 180 degrees out, just not well. I did drive it down the road.
My first 4.3 was vacuum, this engine is electric EGR, so I have no wires in the harness for it, so basically I have a block off plate. I also have no check engine light installed.
I may have a vacuum EGR here somewhere if you need one, I have to drop by sometime anyway.
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Post by gmtrucks on Apr 23, 2013 17:33:04 GMT -4
make sure you have good quality ac delco plugs i put some cheep ones in once and i had the problems you have some times it would run great some times it would miss had have no power
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Dave
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Post by Dave on Apr 23, 2013 18:09:23 GMT -4
Check pick up gear under rotor button ..they are known for comming loose x2 I had this problem with my old s-10 4.3L and after changing everything else it ended up being the pickup
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Post by Cherokee Chief on Apr 23, 2013 19:47:00 GMT -4
EGR would most likely never be opened by the pcm at the speeds he drives and how he is driving.
Is it backfiring through throttle body? if so it would be caused by a lean mixture or a advanced ignition timing, burnt intake valve, bad intake cam lobe, bad intake lifter, bad intake valve springs, bad ignition wires causing crossfire.
Backfiring through exhaust? rich mixture, late timing, bad cam, bad exhaust valve, bad exhaust lifter, bad exhaust valve spring, bad ignition wires.
Other sources would be ignition coil getting bad, bad pickup in dist. Possible tps readings.
These are all guesses of course. But I would start at the basics, check plugs, wires, compression, fuel pressure (not at idle but at time of backfire), check fuel flow (lots of psi but no flow = no go) Ignition timing, (static, centrifugal, Vacuum advanced if equipped, total timing)
Oh and check your grounds, clean and tight
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Post by DamnJeep on Apr 24, 2013 20:04:03 GMT -4
More pieces to the puzzle. Uploaded with ImageShack.usLots of green death here. Soaking the bolts on the EGR and will take it off soon.
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Post by C Monster on Apr 25, 2013 12:43:24 GMT -4
I'm a 305 carb guy, I love them so much I put one in my f150 and bore it too 335 but that's a long story the 305 do have bad cams and have bad lobes on high km motors and could do this with a bad cam whats it got for a exhaust on that rig ? it may be a exhaust restriction like a catalytic converter plugged or muffler or header/manifold plugged
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