2014 XJL portfolio
Recent work
engine and coolant system replaced last summer. (engine blew after the coolant pipe under the supercharger busted while I was on the highway).
After the replacement the timing was bad. So tensioners with the timing adjustment around August.
Starter replaced around October.
Alternator just replaced along with battery.

Finally had a few good months with no problems. I stop to get gas and saw the low battery light. Drove a bit and the battery light came on the dash. Turns out to be the alternator. Got that fixed. Now for the past 3 days it sputters on first start of the day. No lights or codes. After I reverse and start in drive as the engine warms there is no problem. Called Motorcars in Houston. They thought it could be bad gas. Added some sea foam and will see what happens tomorrow. It could be an explanation in that after sitting overnight and all day ( I work from home) water could settle in the bottom of the tank. Motorcars said a light may not come on until the fuel tanks is to 3/4's. I am almost there. The sputter and RPM going up and down doesn't occur on a warm restart. It could be the fuel getting mixed again if it is bad gas. Hopefully the sea foam fixes it. It did sputter again right after putting the sea foam in but the sea foam was on top of a full tank. This only happens on the first start after the car has sat all night and day. It hasn't been as bad the last 2 times the first time felt like a engine mount was busted.

Any ideas? I am hoping it is bad gas but the sputter right after sea foam was added doesn't bode well for that.

 

First is the gas you use "Top Tier" rated ( https://toptiergas.com/licensed-brands/ )? second I use when my idle may be rough a can of BG K44 ( https://www.bgprod.com/catalog/gasol...ystem-cleaner/ ) to clean my injectors.
Top Tier gas has the right detergents and I've always used it and so far haven't had any injector problems, Just my opinion.

 

I sure hope that all that work was done under warranty.

If the sputtering is caused by bad gas, why doesn't it continue to sputter after it warms up? Bad gas doesn't get better after the car warms up.

I'm not a mechanic, but suspect a low fuel delivery problem at startup. I'd check the fuel pumps for proper pressure and maybe a clogged injector.

 

Thanks. Most of the work was with extended warranty or my credit rating would be shot. When they replaced the engine they replaced an injector and soaked the rest in BG. The pump does seem to be a likely suspect. The previous owner had it replaced at some point under warranty. I am not sure exactly when. Funny how the dealership is willing to tell you what has been done after you buy the car but can't say anything before you do.

 

... and quick to to blame it on "bad gas" instead of admitting that it might be a mechanical or electrical problem and running the diagnostics.

 

I'm not saying bad gas, but the detergents used in many gasses are not as strong as the Top Tier rating and over time allow buildup in the injectors. As for the sputter on a cold engine that is when the mixture is richer and may be calling for more gas through the injector and as it may be partly "clogged" it has a bad pattern that can cause a misfire. As for fuel pumps the engine has 3. One is"low" pressure sending gas from the tank to the front pumps that are high pressure and are driven by a short camshaft on the lower right side of the engine. To rule out pumps and filter, does the xj stutter under sustained hard acceleration?

 

The problem is there are no lights or codes. Not ruling out mechanical or electrical. The gas was just a hope. Thinking about it, when Motorcars said they might have to put something in it, The BG (I suspect is what they meant) might have been to clean the fuel system not to take water out like I first suspected. It did it again a little bit today but less severe and for a shorter period. The good news is it seems to be getting less severe and for shorter periods now. So maybe a professional fuel system cleaner like BG instead of the autozone/grocery store/ gas station stuff is needed.

 

Haven't been on the freeway much. I did get on for a couple of miles yesterday. Opened it up and went up to about 70 MPH normally. I only use Exxon or Shell super premium unless I really have to use something else like refueling on 71 on the way to Austin when choices are limited. So the detergents shouldn't be a problem.

 

Back in the day ... ... the "Italian Tune-Up" was a popular way to clean out carbon deposits in the engine and restore performance. That was in the dark ages of trial and error - carburetors with adjustment screws and different jets to try, and no electronically controlled anything. Fast forward to today, with direct injection, high-pressure fuel pumps, FI, MAFs, EGRs, ECUs, CANBUS (unrelated to School Bus), and computers that talk to each other and control everything. So, will the Italian Tune-Up work with today's 5.0L DI engine? Probably not, but if you try it hang on tight for one helluva ride!

 

Update when the gas gauge went past 3/4 the CEL came on like motorcars predicted. Not sure what the codes are but the shop has something to look at rather than just an explanation of the problem.

 

Smoked test showed a plastic pipe had come loose that was causing the misfires.

 

Thanks for the feed back but any more details?
Not sure as there are a number of plastic pipes but a lot of them are cooling parts.
Was this part of the intake system?
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