I have hit a road block with my 5.3 swap
 

I have done a dozen of these swaps and never had this problem or many problems to speak of. This one is in a 70 C10 short bed. The motor has been in and running for over a month. I have driven it around the parking lot at my shop and moved it around the shop a dozen or more times while continuing the build. Last week got the truck out drove around a little and did a few donuts then pulled it back in the shop. Everything was fine an this point. Few days later, start the truck up to move it and its running rough, like a misfire. Checked fuel pressure at this point and everything was at 58 like normal. This week, go to fire it up and nothing, i mean nothing. It will prime the fuel pump, hold pressure and just spin over. Today I hooked it up to the lap top and no DTC's are recorded. Pulled spark plugs and they are firing, pulled the fuel rails, and they are pulsing and have a good fan of spray. It is wired using the stock fuse block like I have done all my others. I have had one die on me before that ended up being the fuse block but it wouldn't do anything, not even prime the fuel pump. Any thoughts would be appreciated.

Re: I have hit a road block with my 5.3 swap
 

Did you pull the plugs? They are surely fouled by now. Sounds like what I call "Lot Rot". Starting it & not driving it over & over will foul the plugs & most likely has a good amount of fuel the oil.

Re: I have hit a road block with my 5.3 swap
 

I have not pulled the plugs, I assumed a running motor was good to go. Have you encountered this before where it was running then just did nothing? Will a simple plug change fix it? Thanks again for the reply

Re: I have hit a road block with my 5.3 swap
 

All The Time when I worked a car lots, They will run, Then run like crap, Then Not run.....You can do a "Clear Flood" procedure on it, Depress the accelerator all the way while cranking. This is hard on the engine tough.

Re: I have hit a road block with my 5.3 swap
 

I have held the pedal to the floor a few times, I'll just change the plugs and go from there. Anyone else have any thoughts?

Re: I have hit a road block with my 5.3 swap
 

Of course as you know, three things required to run- spark at the right time, fuel, and compression. It cant be compression, so Id pull the plugs and see if they are wet. If they are, its either not firing or at the wrong time. If the plugs are dry, its a fuel issue. HTH

Re: I have hit a road block with my 5.3 swap
 

did you check the air intake? is it tight? no holes or loose sensors? what your describing sure sounds like this

Re: I have hit a road block with my 5.3 swap
 

the air intake was on and tight at the time of the decline. Nothing on the motor side of things had been changed between running great and not running. It ran to good to start with to be a problem with a loose sensor or something of that effect. Ill double check of course but it seems unlikely. Thanks again everyone for the ideas. They are all things to double check.

One of our thoughts was that it may have jumped a tooth on the timing chain, but thinking about how that would act, it ran fine after the donuts and when i pulled back into the shop. If it had jumped time the affects would have been immediate i would think.

Re: I have hit a road block with my 5.3 swap
 

ya i know it sounds kinda stupid, but just a couple weeks ago my step daughters lexus started running like crap....the air intake tube was bad...and a few years ago i had a similar issue with my danger ranger..the intake tube was just off the throttle body (you couldn't hardly see it) and was driving me crazy...so when my fuel injected vehicles start acting like crap that the first thing i check

and if it did jump a tooth you'd think it would be immediate

Re: I have hit a road block with my 5.3 swap
 

^^^^^ This is probably your problem. I had this happen back when I was building my street rod. Started fine at first but one day it started running worse and worse. , plugs were wet. I took a propane torch to the ends of them to get them to work again as a test. Finally put new plugs in it and all was well. 70k miles later its still running like a top.

Re: I have hit a road block with my 5.3 swap
 

Thanks. That's my next plan of attack on Monday. I'll report back. Thanks for the responses

Re: I have hit a road block with my 5.3 swap
 

It could be ethenol related as well. Modern fuel sucks. Literally. It pulls water out of the air and without some kind if stabilizer become bad within a couple months.

Again. Related to lot rot.

Re: I have hit a road block with my 5.3 swap
 

Thanks for the advice guys, I couldn't wait till monday so I got a set of plugs from my brother tonight and headed to the shop. We did a compression test on all 8 cylinders, they all passed, and replaced the plugs. Fired right up. I was pleasantly surprised that it was something that simple.

Re: I have hit a road block with my 5.3 swap
 

thats awesome...like the love hate relationship...ya love that its such a easy fix but hate it at the same time

Re: I have hit a road block with my 5.3 swap
 

Do you have a scanner like hptuners or efilive that will show you sensor info in real time?

I once had a similar issue and saw on the scanner my TPS went haywire.had fuel, had spark but did not fire.

Double check cam sensor as well.. they will run with out it, but it can make it real hard to start with out it.

Also, pull a valve cover and confirm you did not loose a timing chain.

Re: I have hit a road block with my 5.3 swap
 

as stated above, 8 spark plugs did the trick.

Re: I have hit a road block with my 5.3 swap
 

I say it was because you fed the truck doughnuts. I run lousy after doughnuts too. :lol::lol:

Re: I have hit a road block with my 5.3 swap
 

Touché ! I like it