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Got the engine break-in blues

B

BayouBlazer88

1/2 ton status
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Jul 31, 2002
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Lafayette, LA
Just fired up the rebuilt 350 (now 355) last thursday. She started right up but didn't idle very well but improved when we adjusted the timing with a timing light. So we went ahead and started the break-in procedure (2000-2500rpm for 20 minutes). She ran great at that rpm but would sputter and almost die when you let off the gas and didn't idle very smooth. I took her for a drive around the neighborhood and she lacked power and would again sputter when I let off the gas. We noticed that the injectors looked like they weren't spraying correctly (the mist looked a little drippy) but other than that, everything was fine. The only other thing we could think of is that we might have a vacuum leak somewhere. The gas in the tank is at least 2 months old, could that be the culprit? The only things that aren't brand new on this engine are the throttle body, plug wires, and distributor cap and rotor. Everything else is brand new. I'll try running some B-12 through the gas tank and check over the vac lines again for now. Any suggestions as to what might be wrong?
 
Sounds like a vaccum leak and the injectors shouldn't drip at all.

85K5 3/4ton,14boltFF,10bolt,9"lift, 35"boggers,16.5x14 welds, big horse 406SBC/700R4 /forums/images/graemlins/k5.gif /forums/images/graemlins/angryfire.gif
 
Mine did the same thing for a while when I put my re-built engine in. For one, the injectors shouldnt drip at all. You need to take them off and get them cleaned. Second, you need to replace the cap and rotor. This is just a must replace item when installing a new engine, even if they both look alright, replace them. Third, the gas would have nothing to do with this. Grnated, the gas may decrease preformance a little, but nothing like you described. When you set your timing, did you unhook the tan and black wire under the brake booster? If you didnt, it would cause the timing to read wrong. Also, check for vacuum leaks. Replace any hoses that look cracked or in bad shape. It would also be a good idea to replace the egr valve. Oh, and finally, check if it is throwing any codes. That would be a good place to start. Let us know....
-Harrison
 
The gas shouldnt be a problem. Before you start doing swaptronics, pull all the plugs and make sure they are all firing. And take notice if they are lean or rich. This will tell you if it is a vacuum leak or not. I wouldnt be suprised if your not firing on all cylinders. With some rubber handle pliers, pull off a spark plug wire make sure there is an rpm drop, and reinstall it. do this with every wire.
 
Yes I unplugged the tan/black wire when I set the timing and also checked for trouble codes and there are none. All the vacuum hoses are new but I'll go ahead and clamp them just to be sure. The plugs are brand new (AC Delco) and I've got some MSD wires coming in on friday. The EGR valve is only 6 months old and the diaghram works fine. I'll run to Autozone tomorrow and get a new cap and rotor and let you know how that goes. Now is there something I can do to clean the injectors other that running injector cleaner through the tank? Or can I pull them out and clean them? Second, how do I tell if the plugs are firing or not? And what does an rpm drop look like? By the way Harrison, how's yours running now? Thanks for the help guys.
 
I let a friend of mine (a service manager at the local chevy place, who actually got the truck for me) work on it. I got fed up of trying everything imagineable, and he though it might be a computer problem that I couldnt test. Anyways I found out that my timing was 20 degrees off because my timing light is broken, it also had a bad egr. Now it runs like a brand new truck, and feels like it has more power than my dad's 99 suburban. As for the injector cleaning, do a search on here. I know about a month or two ago there was a post on here asking about cleaning injectors, and somebody posted up a link to a site that you can send yours to and they charge like $12 an injector to completley clean them. Alsom, you might want to check the fuel filter, it may be clogged. Let us know.
-Harrison
 
Fuel filter is only about 6 months old but I'll pull it off tomorrow and check it anyway. My timing light could be broken too (it doesn't flash at every spark). Saturday is the earliest I can work on it again and if I can't figure out what's wrong I'll have to break my golden rule (Do It Yourself) and bring it in next week. I may have time to mess with it thursday, I'll keep you posted. Thanks.
 
when you pull a plug wire off you will hear the motor drop about 300 rpms. you can also tell if it is totally dead the header tube for that cylinder wont be burning hot.
 
Sounds like my friends camaro we had a hard time getting it to run right...
Changed the spark plugs, then when we fired it up it didn't run right at all... So we pulled all the plugs back out and found we had 1 bad sparkplug out of the package. WTF!?
So we got some new plugs and put them all in... worked fine for about 15 minutes, then started running all crappy at idle kinda like you are describing...
We checked the cap and rotor, and coil, replaced all the plug wires... Then pulled all the spark plugs back out again, and replaced them a 3rd time... Finally that fixed it... i think he may have overtightened one of the spark plugs just a little bit in the aluminum head and cracked the spark plug so it wouldn't work after it got warmed up...

Also, when he switched spark plugs the first 2 times it was running shi#%y, he went from the crush washer type to a tapered seat spark plug... I told him i didn't think that was right, and should stick to whatever type spark plug he had originally which was the crush washer type plugs...
So we got another pack of new plugs and that fixed it. /forums/images/graemlins/rolleyes.gif /forums/images/graemlins/deal.gif /forums/images/graemlins/1zhelp.gif

Never seen that much trouble from spark plugs in my life!
 
I just finished taking apart my throttle body and replacing all the gaskets, seal, and injector filters. Hopefully this will fix my drippy injector problem. Now all I have to do is put the distributor back in, set the timing, and pray that it works. I'll let you know how it goes.
 
Ok I have an update. Took her for another spin today around the neighborhood and then to a freind's house tonight about 2 miles away. For some reason, when the transmission shifts into the next gear, the engine wants to die and I have to give it gas to keep her from stopping. It improves as the engine warms up but still doesn't run like a new engine should. The injectors are spraying a little better than before but still not up to par. All I can think of is a vacuum leak. Also, something weird happened as I was driving home: About a half mile away from my house, I noticed the temp getting to almost 225 before the thermostat finally opened up. That's a brand new 180 thermo in there and the first few times I drove it, it got to about 200 when the thermo opened up like it always has. Strange. Anyway, tomorrow I'll check and double check all the vac hoses and tighten them with some zip ties. Other than that, I just don't know. If I can't fix it by tomorrow afternoon, then into the shop she goes.
 
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