4x4 Related Groups > Tech Talk
5.2 popping through intake?
WagoneerXJ:
So I've recently completed (almost!) a 5.2 EFI Magnum swap in my 97 TJ. I'm having an issue however. It seems to not be running on all 8 cylinders.
Starts up perfectly fine, but it's not smooth like it should be. Give it some throttle and it pops and farts through the intake. Was gettin a CEL for an open injector circuit for a while. Swapped out that injector and code went away.
I'm not sure what's going on with it :'(. I changed out the timing chain, did head gaskets, new intake and plenum gasket etc. New plugs and wires, and I did not touch the distributor at all.
Anyone have any thoughts? Thanks!
Pookapotamus:
Sounds like a timing issue, you might have to check all the timing components, recheck everything to see if you are off by a bit, check the timing chain vs the old one, check the install procedure. Also check the firing order, it sometimes is very easy to mix up two wires. Now you say you did not touch the distributor, it is possible that the timing was messed up before you got it, and installing the new chain in the correct position now means the distributor is now out.
Also do you hear any vacuum leaks at the intake?
Start from scratch and double check everything!
Good luck!
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WagoneerXJ:
Thanks for the advice, I've got some investigating to do!
cLAY:
Did you pull the motor? If not are you sure that whoever did pull the motor didn't pull the dist and then drop it back in? Those Magnum motors are pretty tight to the firewall and I cann't see getting one out of a ZJ without atleast popping the cap off, it still might be tight. Maybe a truck has enough room...You also need a scan tool to set the timing.
Did you change the timing chain before putting motor in or after thinking the problem was the chain? If you did it before then I suspect you got it a tooth out. They can be a PITA to line up.
Mark the lower body of the distributor where the #1 post is. Remove cap so you can see rotor. Rotate engine so that crank mark lines up with the TDC mark. Rotor should be at or just before the #1 mark. If its pointed 180* away then roll the crankshaft over another 360* and see if it lines up. If it doesn't line up properly either your distributor is off or the timing chain is out. If it does line up then pull the valve cover and check #1 cylinder to make sure both valves are loose, this confirms the valves are both closed and are on overlap and you are on TDC compression.
I have had a bad coil cause poor running/backfiring as well.
WagoneerXJ:
--- Quote from: cLAY on September 11, 2017, 02:21:25 PM ---Did you pull the motor? If not are you sure that whoever did pull the motor didn't pull the dist and then drop it back in? Those Magnum motors are pretty tight to the firewall and I cann't see getting one out of a ZJ without atleast popping the cap off, it still might be tight. Maybe a truck has enough room...You also need a scan tool to set the timing.
Did you change the timing chain before putting motor in or after thinking the problem was the chain? If you did it before then I suspect you got it a tooth out. They can be a PITA to line up.
Mark the lower body of the distributor where the #1 post is. Remove cap so you can see rotor. Rotate engine so that crank mark lines up with the TDC mark. Rotor should be at or just before the #1 mark. If its pointed 180* away then roll the crankshaft over another 360* and see if it lines up. If it doesn't line up properly either your distributor is off or the timing chain is out. If it does line up then pull the valve cover and check #1 cylinder to make sure both valves are loose, this confirms the valves are both closed and are on overlap and you are on TDC compression.
I have had a bad coil cause poor running/backfiring as well.
--- End quote ---
Thanks for the insight, Clay. My donor for this swap was a 98 ZJ. I pull the engine myself, it did come out, but was a pain in the arse. Never did remove the cap. I did purchase a new cap and rotor today, just in case.
Distributor was never removed, I've never actually messed with it. I replaced the timing chain back when it was out on the stand. I made sure the marks lines up when I took off the old chain, and installed the new one
the same way. Hopefully I did this correctly!
I'll pull the cap and check to see if it's 180 out. I'm also going to check the firing order again. I'm used to Small Block Fords, new to the Mopar thing. I have a couple spare coils, I'll try one of those, just for fun
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