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Erratic idle


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Pmurphy
Novice

Feb 17, 2015, 3:57 PM

Post #1 of 22 (1237 views)
post icon Erratic idle Sign In

So I've got a '89 GMC 1500, with a 4.3l Vortec. I guess you can say that this truck is prone to having problemsTongue. Long story shorter, had to throw a new 4.3l in the truck. I got it from a local scrap yard because it was the right price. A little while later i noticed that the truck started having low oil pressure, so I layed it aside and started to drive my other car. I'm pretty handy when it comes to engines, so i took out the engine and started to dismantle. Getting to the main bearings they were definitely no good. I got some new ones, got a new crank because the old one had some burs on it from taking it out. plasti-guaged between the main bearings and crankshaft. got a new oil pump just because i was that far into it, might as well make sure that wont go too. After putting it back into the car, putting break in oil in, and starting, its got a wicked erratic idle. It surges very heavily to the point where it stalls. sounds like a vacuum leak... right? sprayed the vacuum hoses, with no change in idle. took off the EGR valve, to find that was on its way out. Replaced that, only to find the same results. checked the air throttle control valve, wasn't too bad, but i cleaned it anyways. Im at the end of my whits, and its grinding me down...

please tell me one of you know the answer?
Thanks for reading my essay of a problem
Pmurphy


(This post was edited by Pmurphy on Feb 17, 2015, 4:26 PM)


Discretesignals
Ultimate Carjunky / Moderator
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Feb 17, 2015, 4:41 PM

Post #2 of 22 (1226 views)
Re: Erratic idle Sign In

If you remove the vacuum line from the EGR, does the idle improve? Any trouble codes stored in the ECM? How does the engine run off idle?





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Pmurphy
Novice

Feb 17, 2015, 4:44 PM

Post #3 of 22 (1224 views)
Re: Erratic idle Sign In

i don't have a code scanner, so i couldnt tell you about that. im not too sure what you mean "How does the engine run off idle?". I'm currently away from the truck, so i'll have to try removing the line from the EGR later.


Tom Greenleaf
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Feb 17, 2015, 4:56 PM

Post #4 of 22 (1221 views)
Re: Erratic idle Sign In

Arrrg. Both old enough and a bum used engine really.


Anything to do with intake not just vacuum hoses.


Is this job just done and still on this break-in oil? I wouldn't use that for what you did to this if just crankshaft and bearing to get oil pressure up.


Probably just me and hope others chime in but by the time and engine is worn to need a crank and bearings I wouldn't mess with it at all anymore - done for better or whole crated engine or keep looking for even at the age an exact fit one that's perfect.


IDK, didn't save anything that this engine was a bargain and not so sure it's worthy of what it got already from you. How is it with compression and get that damn oil out, if done and checked right before first start up for bearings like that with new crank what are you breaking in? If all that's new what was that for? They didn't use break in oil in this when it was new so why now? You didn't mention cylinders at all,


T



Discretesignals
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Feb 17, 2015, 4:57 PM

Post #5 of 22 (1218 views)
Re: Erratic idle Sign In

You don't need a code reader for that one. You can jumper A to B in the ALDL and count the flashes of the check engine light.



Tom has it right. If the crank and rod bearings where torn up, it is a good beat the camshaft and cam bearings don't look too good either.





Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.

(This post was edited by Discretesignals on Feb 17, 2015, 4:59 PM)


Pmurphy
Novice

Feb 17, 2015, 5:44 PM

Post #6 of 22 (1208 views)
Re: Erratic idle Sign In

ya i didnt think to rip into that, looks like i might be in a little bit of trouble, but my oil pressure is no longer the issue anyways? im having problems with my idle


(This post was edited by Pmurphy on Feb 17, 2015, 5:49 PM)


Hammer Time
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Feb 17, 2015, 7:14 PM

Post #7 of 22 (1200 views)
Re: Erratic idle Sign In

They didn't make a 4.3 Vortec in '89. TBI only



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Pmurphy
Novice

Feb 17, 2015, 7:23 PM

Post #8 of 22 (1197 views)
Re: Erratic idle Sign In

engine was out of some other car, its from a junkyard.


Hammer Time
Ultimate Carjunky / Moderator
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Feb 17, 2015, 7:25 PM

Post #9 of 22 (1195 views)
Re: Erratic idle Sign In

It's still not a Vortec. You don't have an operating system to manage the system on a Vortec.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Feb 17, 2015, 7:26 PM)


Pmurphy
Novice

Feb 17, 2015, 7:43 PM

Post #10 of 22 (1191 views)
Re: Erratic idle Sign In

ok, its got the TBI on it, none the less, not solving my problem


Hammer Time
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Feb 17, 2015, 7:47 PM

Post #11 of 22 (1189 views)
Re: Erratic idle Sign In

Did you try pulling the EGR hose off as DS suggested?



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Feb 17, 2015, 10:55 PM

Post #12 of 22 (1177 views)
Re: Erratic idle Sign In

Quote">>engine was out of some other car, its from a junkyard.<<"


It belonged there from the get go. What do you really have cobbled together here at all? Missed that word "Vortec" and '89 wasn't so trouble from that alone and is engine really from a car not a truck? Not sure what you can use car to truck - the salvage yards match up whole engines.


I think if the rest of this truck is in nice shape start over with the right engine at least and one with full check out before you even begin or IDK what you'd find for a whole crate engine rebuilt and if you still have enough OE stuff from original engine now either.


Has this been driven at all yet? Sorry if I missed that but if you've managed to get a "car" engine in this you may be screwed and will look in a bit to see if the truck engine is counter rotating or what for a 4.3 if so you now have a huge paper weight,


T



nickwarner
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Feb 18, 2015, 2:52 AM

Post #13 of 22 (1171 views)
Re: Erratic idle Sign In

I don't suppose you have done a compression test on this have you? Your junkyard motor that was at such a good price was so wheezed out the mains were shot. Gotta wonder if your piston rings are a matched set to that.

If I had it torn down far enough to see junk mains, it would be getting a full rebuild in my garage. Getting your oil pressure numbers to go up doesn't mean you have a good engine, it just means you have oil pressure.


Hammer Time
Ultimate Carjunky / Moderator
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Feb 18, 2015, 3:07 AM

Post #14 of 22 (1169 views)
Re: Erratic idle Sign In

The 4.3 V6 was only used in trucks, not cars.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Feb 18, 2015, 3:19 AM

Post #15 of 22 (1165 views)
Re: Erratic idle Sign In

Chevy Caprice used a "Z" code engine in '89 same as this if look up was correct? Still doesn't mean ready to bolt in to me. Said earlier that if an engine needed anything close to this it would get tossed but not for another just as bad. It's getting old for good known used, fully checked out engines so that leaves a redone one to me or forget this truck, T



Hammer Time
Ultimate Carjunky / Moderator
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Feb 18, 2015, 3:23 AM

Post #16 of 22 (1162 views)
Re: Erratic idle Sign In

Yep, you're right, they did use that fr a short time in the Caprice. I forgot about that.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Feb 18, 2015, 3:42 AM

Post #17 of 22 (1158 views)
Re: Erratic idle Sign In

I think this thread is going to be done with. Engine is too old (I SAID THAT!!!!) for used unless remarkably lucky to find one you could run still in a vehicle and test out before swapping a thing.


Two places here for salvage yards pull engines after totally checking them out with known history as best as possible, compression results and know what will be an exact swap.


Been a long while but wouldn't do the swap just the diagnosis and go myself and check engine, pull a valve cover if already on a crate or whatever the situation for a good guess at sludge - pass on any of those AND go look at the vehicle it came out of for info. Find last inspection results, how long it had been out of service and why - like nice to find a side wreck or rear and of course some with rust beyond repair but engine can be fine.


Different world - Junkyards don't want to fail either and warranty 100% the engine for either 90days or longer depending not for labor just another engine.


Virtually all were going into fine vehicles that some horror happened to blow an engine like a drain plug, oil filter or oil pan damaged by something and a surprise seize up and vehicle was worth it, T



Pmurphy
Novice

Feb 18, 2015, 4:13 PM

Post #18 of 22 (1137 views)
Re: Erratic idle Sign In

once again, oil pressure is no longer my issue. The engine came out of some car that got in a car crash and was totaled. ive had this engine for about 4 - 6 months and im not exactly sure what it was out of, it was already removed when i got there. The bolt patterns were all the same, so i bought it and it worked for the time being. the engine is back in the GMC from when i was done with the bearings and crank. But my problem is ERRATIC IDLE, not low oil pressure anymore. Im baffled by how many times i have to say that


Hammer Time
Ultimate Carjunky / Moderator
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Feb 18, 2015, 4:32 PM

Post #19 of 22 (1134 views)
Re: Erratic idle Sign In

You still haven't tested the EGR valve as you were advised twice. Please don't post again if you haven't followed the instructions you were already given.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Pmurphy
Novice

Feb 18, 2015, 4:39 PM

Post #20 of 22 (1132 views)
Re: Erratic idle Sign In

i forgot to add that to my last post. there was no change in idle from taking off that hose


Hammer Time
Ultimate Carjunky / Moderator
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Feb 18, 2015, 4:58 PM

Post #21 of 22 (1128 views)
Re: Erratic idle Sign In

OK, and the codes?



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
Ultimate Carjunky / Moderator
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Feb 18, 2015, 6:11 PM

Post #22 of 22 (1122 views)
Re: Erratic idle Sign In

Quote from back a few">>But my problem is ERRATIC IDLE, not low oil pressure anymore. Im baffled by how many times i have to say that<<"


That's the problem - the damage done (highly likely) by having low oil pressure because of a worn crankshaft did harm to everything else in the engine! It was a core to rebuild not just one thing. I doubt the worn crank happened while you had it but was just a running engine and was saved and probably shouldn't have been?


T







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