[Danny_54]

So I just changed my spark plugs with Autolite Iridium Tip XP985 plugs. I followed this guide when I did the change http://www.4x4xplor.com/sparkplug.html but I didn't use as much anti seize or dielectric boot protector as he did.

The plugs were all gapped to between .030-.035. But for some reason, my Jeep is having a rough time starting.

It will crank for 2-5 seconds longer before finally starting. It has mainly been doing it from cold start. When the engine is warm it usually fires right up. However, it never did this before with the old plugs (even though their gaps were .060-.075 when I pulled them).

I'm not the most knowledgeable when it comes to vehicles but I enjoy learning and reading anything I can about it. Any experience or help would be greatly appreciated.

Thank you, Danny

 

[slomaro]

How does it run after starting? I just changed my plugs - at night, with poor lighting, and probably too many beers - and when replacing the spark plug bar one of the boots went to the side of the plug instead of on it, so I was only hitting on 5 cylinders. having worked on quite a few motors I noticed the miss as soon as I fired it up, and then realized my mistake. just a thought

 

[Jerry Bransford]

It's not the spark plugs causing the issue, those plugs run well in TJs and I'm running them myself in my '04.

I suspect something to do with the ignition wiring or ignition rail you had to reinstall. Double-check all the plug boots are seated over the spark plugs and in the correct order if your TJ has a distributor, and the boots may not all seat properly over each spark plug if you have the coil rail.

 

[Danny_54]

Yeah I suspected it wasn't the plugs. It runs fine after it starts, it just takes more time to crank to start. Thanks for the responses! I'll go check the ignition rail.

 

[Jerry Bransford]

Try this... humor me... when the engine is cold or maybe tomorrow morning, without turning the ignition to Start, cycle the key on-off-on 3-4 times so you hear the fuel pump cycle on-off-on a few times. Then try starting the engine. If the engine starts right up, the problem is with the fuel pump assembly's check valve leaking gas back down to the gas tank... not anything to do with the spark plugs.

 

[Danny_54]

Jerry, I just tried what you said and it was better, not quite perfect but better. I'll definitely try that tomorrow morning when it's nice and cold before I head to work.

I'm just curious, even though it started fine before the spark plug change, what made you think of the fuel pump? Just would like to gain some insight into your thought processing and learn something new.

The help is greatly appreciated!

 

[Jerry Bransford]

It just didn't seem right that simply installing new plugs would make the engine take longer to start yet run fine once it did start. That is a classic bad fuel pump assembly check valve symptom so that's why I suggested you try that on-off-on procedure for the ignition switch. It was pretty much coincidental that you noticed the slow start with the new plugs.

 

[Danny_54]

Jerry, thanks for the reply. I'm pretty sure that's what it is because the on-off-on procedure seems to help it start a lot better.

It starts a lot quicker with that procedure so I'll take a look into the check valve.

Thanks again!

 

[tangofox007]

It starts a lot quicker with that procedure so I'll take a look into the check valve.

You will not find a check valve. The problem is with the pressure relief valve in the fuel pressure regulator. The valve is not a servicable component, so the only solution is a new fuel pressure regulator.

It is worth noting that folks have tried installing a check valve in the fuel line with very poor results. Unlike the pressure relief valve, a check valve will allow pressure (from heat following engine shut-down) to build to the point of rupturing the fuel line.

 

[DP40]

Where is the fuel pressure regulator located?

 

[Jerry Bransford]

The FPR is located on top of the gas tank, it plugs into the top of the fuel pump housing. I personally have changed the fuel pressure several times to try to fix this particular problem and only once did it seem that a new FPR fixed the problem. Replacing the entire fuel pump/FPR assembly is the only way it has fixed this issue 100% of the time for me.

This shows one of the times I replaced my FPR, I stopped replacing them as a fix for my two TJs and a couple friend's TJs once new new FPRs didn't fix the issue 100% of the time. I believe the issue of the FPR not fixing it 100% of the time due to the Factory Service Manual confirming there are actually two check valves... one in the FPR, the other in the output of the fuel pump itself.

This is per the Mopar Factory Service Manual... "The regulator acts as a check valve to maintain
some fuel pressure when the engine is not operating.
This will help to start the engine. A second check
valve is located at the outlet end of the electric fuel
pump."

Due to all the work required to drop the fuel tank, I'm no longer willing to throw the dice on whether replacing the FPR by itself will fix the problem, I now replace both the FPR and the fuel pump with a Bosch assembly as shown in the last photo. That has been the only 100% fix I now trust having replaced them all more than the average bear has.

 

[Danny_54]

Would you go with the Bosch fuel pump assembly or a Mopar fuel pump assembly? And how long has your Bosch pump lasted?

 

[Danny_54]

Bump. Should I go with a Mopar pump? Or will the Bosch last as long as the Mopar one?

 

[Jerry Bransford]

Either is good, I'm currently running Bosch. Just avoid Spectra or Airtex.