my 88 xj has been backfiring and over heating.
I can fire it up and it will idle good but as soon as I advance the throttle it backfires through the exhaust no matter what I do.I have replaced2 sensor,crank sensor,map sensor,injectors,fuel press regulator,knock sensor,checked timing not 180 out,re seated valves,gone all through vacuum,checked resistance at tps,cleaned idle control.
I am at a loss please help.



p.s.
just found very small nick in the pickup coil

 

Backfiring through the exhaust can mean a "rich" fuel to air condition.

For this symptom, the first test I perform is a fuel pressure test (even though you have replaced your regulator). Gotta have data.

For your 88, you should have 31 psi at idle. Then disconnect the vacuum line leading to the fuel pressure regulator (be sure that line is pulling good vacuum) and the pressure should jump to approximately 39 psi.

The overheating could be a separate issue. What is the condition/age of every one of your cooling system components? That stuff needs periodic replacement. No better money spent, than that spent on cooling system maintenance.

 

tested fuel pressure today.at idle it ran 29-30 psi and with the vacuum removed it just shook over 31 but no 39.replaced fuel filter with no effect.

 

Did you check to see if the vacuum line leading to the fuel pressure regulator HAS good vacuum? I'd say you have either a vacuum issue or a regulator issue. Fuel pressure should jump to 39 psi with that line disconnected.