I am working on my first ever engine transplant. It has been quite the learning experience. I put a 5.7 Chevy 350 Vortec V8 from a 99 Suburban in my Jeep YJ Wrangler. The block/headers were professionally machined/rebuilt and the suburban was running fine when I pulled it. All parts were cleaned and inspected before re-installed.

The problem I'm having is that it starts fine and idles at about 700 RPM. There is a slight shudder which might be a misfire but I'm not 100% sure. When I try to apply throttle it starts to rev up and then cuts out. If I hold the throttle steady it will keep going up and down with an occasional small backfire. Through all of this the computer is not throwing any codes, besides the p1345 code which I cleared with setting the cam retard. No matter what I hold the throttle at, full open or 1/4 it has the same reaction. Except if I barely give it any I can rev to about 1500 rpm before it starts cutting out.

Here is what I've tried to diagnose this (based on suggestions from this site and other sites), in no particular order:

Reset the timing (i.e., started from TDC and made sure distibutor was in proper starting location) twice. Used scan tool to make sure cam retard was within 2%

Tested fuel pressure. (Getting 62 on key on engine off, drops to 54 when started and up to 58-60 when applying throttle). This is true through all the following:

Inspected fuel lines, pump filters (have pre filter, e2000 pump and after filter) and have found no leaks. Tried different combinations of removing/exchanging filters and no change in pressure. Replaced pump, no change in pressure. Replaced fuel regulator (before changing to MPFI) with no change. Closed return line (before changing fuel regulator) and PSI jumps to 100 PSI (which fuel pump is rated for). Fuel pressure holds at 50 for at least a minute after shutting off engine and still is between 40-50 several minutes later.

Removed intake cover, reconnected fuel lines and check for fuel spider leaks (none). Cleaned all poppets and tested injection. All injectors shooting cleanly and at the same rate. I also replaced the fuel spider with the newer MPFI one.

Cleaned MAF. Unhooked MAF, idles horribly but still has same problem with cutting out.

Replaced Throttle position sensor

Cleaned EGR. Tested voltage of slider to make sure it wasn't stuck and sliding properly.

Tested all spark plugs and wires. Visually inspected all plugs with rechecking of gaps.

Tried with O2 sensors unhooked. No change

There may have been some things missed that I've done. My brain hurts at this point.

I have not run a power balance test yet. That is on my list, but at least I'm getting spark and fuel at each cylinder.


I'm really at my wits end trying to figure this out. Any suggestions will be welcome.