Hi everyone. I've been reading this forum for awhile trying to figure out my problem. I recently inherited my my grandfathers 79 xj6. I love it however it has sat for awhile. So here's what we've done. New fuel tank in passenger side. Fuel pump cleaned the lines. Fuel filter cleaned the injectors. The car will start(not great) you can rev it all the way. Sounds good. However once you are in gear and start to go it bogs down. Back fires will barely move. I would love to get this going for the summer. Any ideas I really appreciate

 

is it carbed or fuel injection?

my car did the same thing recently when I ran out of gas, backfiring and all, after I put fresh gas in the driver's side tank, something which it never does or has done before. Yes, new filter and fuel pump too.

I gave up trying to start it and left it alone charging the battery.

Next day I tried again and it started and ran as if nothing had ever happened. Really weird.

did you check the transmission fluid level too? The dipstick has a cold and hot mark. Read the Cold mark with cold engine.

try this:

1) put the shifter in First gear;

2) turn the ignition switch as if to start the engine but hold it in the START position for 3 or 4 seconds, then back to OFF. You should hear the fuel pump(s) whirring / humming as you hold the ignition key in the START position.

3) do it 3 or 4 more times while changing tanks each time, (shifter in First gear).
The fuel system should now be "charged" or "pressurized" after doing the above.
That's how I start mine after the car sits for a while, it never fails.

4) then place the shifter in PARK and try to start it normally.

 

Thanks Jose for the response. It's fuel injection. I will double check the transmission fluid. I will try to start it that way and see how it works. Thanks again. Appreciate the help

 

if no go after trying the above, then there is a No Start Checklist that Doug posted in the XJ HOW TO QUICK LINKS at the top of the forum thread list in this page.

 

The 'could be' list is long but I suspect you still have some bad/contaminated/rusty fuel. The long storage/contaminated fuel/bogs down/backfires scenario is one we've seen many, many times. One round of cleaning doesn't always do the trick.

You mentioned on new tank on the passenger side, but what about the other tank?

IMO.....Before you get 'bogged down' (sorry!) with other possibilities remove the fuel filter and empty the contents into a clean jar. What you see will dictate your next move. It'll only take a few minutes. If it looks clean and fresh you can move on to other problems. If it's cruddy, well, you still have some fuel system work ahead of you.

Cheers
DD

 

Well you gotta check all the basics. Sounds like you went trough the fuel system but as previously stated remove the filter again and make sure it's not plugged up.

Here is how I would approach it. Fuel... spark... compression....

Fuel...Seems like you got the fuel supply system managed. Try unplugging the air meter. When they sit the resistance contacts corrode. Unplugging it will put in a failure mode and the car should idle. Check your fuel pressure. Should be about 38PSI. Get a 9v battery and some leads. Disconnect each fuel injector and connect the 2 terminals of the battery to the 2 terminals on the injector. You should hear an audible click and see a residual pressure drop on your fuel pressure gauge if you have one.

Spray some brake cleaner down the intake while it's running...if it runs better you've got an under fueling condition, if it runs worse you've got an over fueling condition. If it run about the same you've got an ignition or mechanical problem. Depending on the results check the Coolant temp sensor resistance. The values should change as the engine heats up.

Spark... Check your ignition timing. Get a spark tester like the one linked below and make sure the spark is blue and strong enough to jump. A red or orange spark is no good.
Inline Ignition Spark Checker

The I6 is super easy to do a compression test on as the plugs sit right at the top. Not unusual for these engine to have a dead cylinder.

Just run it for a while. Make sure you've got oil pressure and run it. An engine that sits for a long time can develop varnish that can hang up the valves and stick the rings. As it runs you may notice it gets better. You have to check all the basics first though becasue a misfiring cylinder will just wash out the oil with fuel.