Popping Narrowed Down Please God Help Me

Why do the truck gods mock me so? I've got a 93 chevy 1500 350 5.7 tbi. I got a used engine, not rebuilt but used. This is the third engine the truck has had. Wife has a lead foot, but more on that later.
Started the engine, sounded strong, oil pressure jumped up to 30 psi as soon as it started.
Check engine light came on. Then popping through throttle body. Read alot about timing. Adjusting the timing to TDC as specified in the Chilton's manual. Popping still heard in the throttle. New plugs, new wires. With the engine running, I removed then replaced the wires from the distributor. When I got to number five and removed the number five wire from the dizzy, the throttle backfire stopped completely. I have little to no power when I try to drive the truck and my oil pressure dropped back down to danger zone after I let it idle for about 10 minutes. Should I whip out my compression gauge or should I whip out my baseball bat and try to get the money back from the guy that sold me the crap engine?
Any advice would be great.
Brian 1993 Chevy 1500 "My Daddy gave me that there truck"
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
How long have you had that engine?? Has that engine always maintained 30psi of oil pressure or have you even had it long enough to know?
I would look at the compression all the cylinders. Take note of each and compare #5 to the rest. The fact that the backfiring stopped when you disconnected the spark plug wire leads me to believe the valve is burned. If so you could be igniting a mixture that's pushing its way back up into the manifold (not good) and hence it stops when you disconnect the plug wire.
For some reason I'd think the oil pressure isn't related. On my old Dodge Van, the oil pressure would drop significantly while idling after warmup. It'd be ok when driving. But that sounds like an oil pump that's worn with age.
Not sure what, if any recourse you'll have against the guy that sold you the engine. If it's old with a lot of miles on it, there's probably not a lot you can do. It comes with the territory when buying used parts.
~jp
brianwrites wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I agree with this. Also I have seen a worn exhaust cam lobe cause the same problem because it was not letting hot gas get out quick enough and causing it to pop through intake. Either way it does not sound good and a compression check is a good starting point. ----------------- TheSnoMan.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I've had the engine for about two weeks. Put it in last weekend, been working on it every since.
And just when I was starting to make lemonade, my damn lemons have spoiled on me.
Well, I took the valve covers off. Checked out the rocker for the cylinder number 7 exhaust valve. Low and behold the rocker was completly loose. I thought I'd adjusted them all properly. So I tried to do it again and no matter how tight I got the nut, the rocker never even touch the push rod. I even bottomed out the nut and the push rod still didn't touch the rocker.
Dead lifter, bad cam lobe, burned valve all of the above? What do you think? Best scaneario I pull the intake manifold, replace the lifters and camshaft. Hell, if I do that, might as well pull the heads and replace the vavles right?
Sounds like I'm gonna be putting engine number three in the truck right? Is it pathetic that I have three chevy 350 engines at my house and none of them are worth a crap?
I plan to do a compression test today, but I think it's a moot point now. I think I get to finally rebuild an engine. Dammit!
Brian 93 chevy 350 "Boy, what chu done to my truck?"
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Well, if the seller made any guarantees, I'd hit him up first...
Aside from that, yep...looks like you're going to be tearing that one down. Check the cam and lifters. Based on what you're saying now, I'd lean toward Snoman's advice that it could just be the cam, and not necessarily a burned valve.
Are either of the other two cams good? I'd install new lifters and make sure they're broken in with whichever cam you install. But a new cam and lifter set will run you under $150. Besides, you can take the opportunity to install a good "truck" cam that'll give you better gas mileage and more low-end torque.
I'd pull the heads just to inspect everything. If the valves are ok, then I wouldn't screw with them.
Did you ever check compression on the other cylinders? I'd compare them against some known numbers. That'll give you a good idea as to the condition of the rings. If the bottom end is ok, I'd invest in the new cam, slap it together, and run it till it dies.
Also... Use the fact that you have 2 extra engine at your house to your advantage. Inspect both and choose the better of the two blocks. Strip that one down, and have the block hot-tanked and inspected by a competent shop. Shouldn't cost all that much. Get a good rebuild kit and start putting it together. Do this for the heads as well...clean them up, install new valves, springs, or rockers as needed.
Sell the other engine in pieces (block, crank, heads...) to help offset the cost of this. The good thing is, this could be a good project that you can put money and time into when you have it. When the 3rd engine dies, you'll have a freshly rebuilt engine ready to go. Or, pull the 3rd engine, sell it too, using that money to further offset the cost of rebuilding one of the others.
~jp

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

You know this kinda sounds like the lifter is completely missing from bore. Even if lobe was worn he should have still been able to contact push rod. He might pull another rod and check the length of it and confirm that valve is not stuck open too. I would like to here what he finds on this one because it would take some very serious cam and lifter wear to do this otherwise. ----------------- TheSnoMan.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I had the same thought after posting. My thought was that the pushrod was the wrong length, although I can't imagine how it would've gotten in there.
Also, I think it's unlikely that one lobe would've worn down for just one cylinder. If it didn't happen evenly across all lobes, it would lead one to think that something catastrophic had happened and the lobe, or some other piece of the engine was sheared off. If that happened, lifter adjustment should be the least of his worries.
~jp

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I would not just replace the lifters and not the cam for you can't do one with out the other. Could have bent the pushrod? (just my two cent)
wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I have seen it happen where just one lobe was wiped clean off more than once and I had it happen to me with a old Slant Six many many years ago. It was a exhaust lobe too and all the others were fine. It happened during a 200 mile trip. ----------------- TheSnoMan.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
All very good thoughts. I compared the pushrod with another and they are the same length. Dammit. I did, as best I could, inspect the lifter with a flashlight through the headers. It looked very suspicious. Not at all like the other lifters. If fact...gulp...it like it was either stuck or (insert catastrophic music here) missing.
After working on this for two weeks straight, I've decided to walk away from it for a few days. Perhaps this weekend, I'll try pulling the heads, and swapping out the lifters and camshaft with one of my other engines.
I'll admit, I am a bit excited about the chance to rebuild an engine. Although it means a lot to me to get my daddy's truck up and running.
You guys have been great. I'll keep you posted. Did I mention I'm a writer and really have no expertise practical mechanics at all? Thanks again fellas.
Brian '93 Chevy 1500 www.brianwrites.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I would pull the intake and see what you find and then go from there. It is not a lost effort because it will make engine a bit lighter to pull and give you several options on which bolt hole to hook a chain to, to balance it on hoist ----------------- TheSnoMan.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I posted this yesterday, but it didn't take. Google has been upgrading their system.
Anyway... I visited your website, and saw that you're in Stone Mountain. I'm about 5 miles away in Grayson/Snellville. If you'd like, I'm willing to trade services for services. I'm no pro mechanic, but I'm real interested in rebuilding an engine. I also will need to chance my cam soon, as it's totally wrong for my truck, and therefore I'd like to run through the process, or at least be there when it's done, before I tackle my own.
If you're willing to help me swap axles in my truck sometime in the next month, I'd make myself available to help in any way I can. I'd just like the experience.
Let me know what you think.
~jp

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
In 86, I had a buddy with an 81? (the last of the 71?-81?) z28 with a 350. It had a very light, steady miss at idle. ALWAYS.
But under load, it ran smooth and still had a lot of power.
A good parts guy (our boss) suggested an intake cam lobe was gone. Sure enough, one intake lobe was as smooth as a bearing journal. There was a hunnerd dollar bet on it too.... but the boss didn't make him pay. I would have never believed it if I hadn't seen it with my own eyes.
skimmer
wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I've adjusted the timing several times and after each adjustment, the next time I start it, it jumps time. Is the ECM gone? Or perhaps a bad ignition moudule? I haven't torn it apart yet, hoping there's something small that I'm missing and it's gonna work itself out...I doubt it.
Did a compression test and everything checked out fine.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

If it is jumping time there is something loose somewhere because the ECM does not do much with base timing (you are disconnecting the electronic advance at jumper on firewall when you time it right?). YOu might check to see if timing chains is worn out. This is easy to check by laying on ground under a warm engine and grabing dampner with hand and seeing how far it will turn before you take up slack in chain. (turn it back and forth for total range of sloop and you will feel when you "pick up the cam") It should be 5 degrees or less if it is still fairly snug and if it is about 10 degrees or more you need to replace timing chain. ----------------- TheSnoMan.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Hmmm. Turning the damper by hand. I would think it wouldn't turn at all. But hell, I'll try anthing at this point.
Engine number two(that's in the shed)...I began taking it apart. I replaced that engine because it seized up. Many suspected that during the year's time it lay dormant in the garage, something fell into the lifter valley or dizzy hole and jammed it up. Well I loosened the rocker arms, first on the right side...still seized up. Then I took the rocker arms off the left side. Suddenly the engine was fine. I put a socket wrench on the crankshaft and it turned over just fine. Any ideas?
Could the lodged item have fallen loose? If so what are the chances it's down near the pistons rods?
On another note, what's your preference when pulling an engine. Up and out through the hood with the tranny atached , or do you prefer removing the front end and simply sliding it out.
Sounds like my recently acquired engine is junk. Because from what I'm hearing, I've gotta pull the intake manifold, remove the lifters, pull and inspect the camshaft(probably replace). Nail down my timing problem and them possibly replace the oil pump.
On another note: Jeez I've got mechanical porblems. Any advice on crankshaft removal. On the original engine(that's also in the shed) I started tearing it down and got as far as the crankshaft. Was I supposed to turn the engine to TDC before tearing it down? Because the current crankshaft posistion is such that some of the nuts at the bottom of the pistion rods(not sure what these are called) are not accesible. And of course the crankshaft on this orginal motor won't rotate becuase two of the pistions are rusted to the cylinder walls.
Did I mention that I can't pull the lifters out of the orginal motor either. I think I'm gonna take up bicyle repair as a hobby.
Thanks for any help.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

YOu should be able to do it to the point you pick up cam because it should turn easy in cam chain slack.

Maybe it hydro locked or sieve for lack of oil on piston and no it is free for moment (not the first time that has happened)

I would pull pan to figure out why it locked up and check bearings for damage.

I take them up and out and usually leave tranny behind in truck. It is not just the size, it is the extra weight and CG shift to deal with

Before you pull engine again, remove intake and get a better grip on things. I have had cams go bad and replaced them and rack up a lot of miles afterwards

Rotate block on stand so one set of cylinders is straght up and fill them with diet pepsi (yes the pop) It has phosphuric acid which will eat rust and the diet will not add any sugar goo to it. Let it set for a day or two and repeat for other side. That should free up pistons though you might stil have to still shck a few with a dead blow hammer.

When that happens it is because they are either varnished/gummed up badly or mushroomed from wear. Invert motor (vallve galley aimed down and fuel pump removed if it was a carbed motor) and with timing chain removed spin cam a few times and then remove cam, reinvert bolt right side up and tap lifters out through bottom.

TheSnoMan.com
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
You know, there's nothing like solving a good mystery and learning a great lesson from it. As you may recall, I had backfire or popping through the throttle. Adjusted the timing, still had the problem. Removed the plug wires to the dizzy one by one and narrowed it down to cylinder 7. We all sort of agreed that the exhaust valve was not opening and perhaps there was a flat cam lobe.
Well, for practice, I removed the camshaft from one of my old engines in the shed. That's a lot of freakin' work! At that moment, I hoped I would NOT have to do that repair to the engine currently in the truck. I removed the valve covers and saw that the pushrod for exhaust valve 7, was completely lose and no amount of tightening would take out the lash. With a flashlight I could see(without removing the intake manifold that the push rod was sitting rather funny in the lifter.
Back to the old engine in the shed, I started tearing it down, just to get away from the truck. I removed some of the lifters and when a few of them came out, the three-sided retaining clip popped out and so did the small bowl-like object in the top of the lifter. Hmmm. I wonder...
Sure enough, back to the truck I went, removed the intake manifold and sitting in the lifter valley was the bowl-shaped object from the top of the lifter for exhaust valve 7. The depth of the bowl was just enough that the pushrod would sit in the lifter, but now allow the cam movement to have any affect on rod and open the exhaust valve. I put another lifter in the older lifter's place, hand cranked the engine and sure enough the lifter goes up and down as does the pushrod and rocker arm. I guess I'm pretty lucky seeing how the object did fall down into the crankshaft.
Anyway, it's time for reassembly and repairing the fuel lines and throttle body(I cross threaded the inlets on the back of the throttle body and now it leaks fuel)
Thanks for everyone's help and perhaps this will help someone else in the future.
Brian 93' Chevy 1500 "The truck's almost ready, Daddy!"
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Good to know Brian. Sounds like you're on the road to recovery. Hopefully it'll work out well for you and you'll end up with some more time on that engine. In the meantime, I'd suggest that you do go ahead and rebuild one of the other engines. It'll be extra experience, and you'll have another engine ready to go when the time comes.
Again, if you need help, you've got my email address...I'd be glad to get in on that, as it'd be good experience for me as well.
~jp

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.