Switched Over to Complete Synthetic, Noticed Weird Noise

Yesterday I decided to make the switch over to complete synthetic oil. I have been running a synthetic blend of Valvoline High Mileage 10w-30 the last 30-40k. I changed the oil yesterday and put in Valvoline Synpower 10w-30. My 99 is currently sitting at 162k. After letting it run for a little bit after changing I noticed a ticking, or clunking sound coming from the engine bay. Is this because of the synthetic oil? If so, is that bad or good?

Also, I have been having trouble the last few weeks getting it started. It turns over, but wants to continuously crank. When it finally starts, it sputters, almost dies, but recovers after pumping the gas pedal. After starting it several times last night after changing the oil, this happened every single time, not sparingly like it has over the last few weeks. Any correlation between the two? Btw, the CPS was replaced over a year ago, so hopefully it isn't that again. Fuel pump maybe?

Try replacing your Fuel filter. Ive noticed that when it gets clogged it takes longer to start. Just a thought.

KryptoniteXJ said:

Try replacing your Fuel filter. Ive noticed that when it gets clogged it takes longer to start. Just a thought.

Click to expand...

No external fuel filter on the 99's.

there is a filter inside the tank w/ the fuel pump, it will cause the prolonged cranking. mine is doing it. pita to get to though and change.

As far as the oil goes, I switched over to full synthetic 40K miles ago with excellent results. No ill effects or sounds. Just longer change intervals, and a sqeaky clean valve train, no sludge, gunk or other crap. If I had it to do over, I'd do just the same.

jeepster_259 said:

there is a filter inside the tank w/ the fuel pump, it will cause the prolonged cranking. mine is doing it. pita to get to though and change.

Click to expand...

I'm curious how many miles on your Jeep? I'm wondering how long those in tank filters last.

The long start is not your crank sensor. Try the "poor mans prime" to help diagnose your long crank to start issue:

1. Turn key to ON position (don't crank engine)
2. You will hear the fuel pump energize and run for about 2 seconds, then turn off
3. Turn key to OFF position
4. Repeat above 2 more times
5. NOW crank the engine.

Does it start quicker? If so, you are probably experiencing a failure of the check valve located on the fuel pump assembly, located inside the tank. It is a very common failure on your vintage, mine gave it up around 85k or so. It does NOT mean that your fuel pump will leave you stranded; you can live with it like this indefinitely and do the poor mans prime if you like.

Eventually though when it ticks you off enough and you have a few extra shillings, drop the tank and replace the entire fuel pump assembly (consists of fuel pump/filter/regulator) and that should take care of it.

One last thing to mention and it's a long shot. Be sure that your battery is up to snuff. Marginal batteries have been traced to long crank times. Sounds weird but it has happened.

BTW: I really don't see a correlation to switching from dino oil to synthetic. I'd just keep an ear to it and maybe use a mechanics stethoscope to help diagnose exactly what you're hearing. Don't want to assume anything; could be a noisy fuel injector, etc. etc.

The synthetic oil will clean the inside of the engine. Maybe some sludge got loosened and clogged something. One thing to be mindful of is an old starter motor taking too much amperage to work properly. My '92 began to have trouble starting, so I replaced it with a rebuild. It failed in a few years, so I got a new one. Wow!- it couldn't start fast enough. I got it at Advance, back then about $100. Also, make sure the throttle body, and especially the idle passage, is clean. Hitting the pedal while starting is just cheating air past the throttle plate, and goosing the injectors, helping the engine to start. Honestly, at 160K+, any of the above suggestions could need attention. Do the later XJs have a plastic tank? I ran into similar problems with my '98 ZJ, turned out it was the plastic tank deteriorating, and it clogged the sock, which overheated and burned out the pump.