Rev.LowBuck

98 4.0/auto trans with 160,000 miles. Seemed down on power and a week or so later the check engine light came on and a slight miss was detected. Parts store OBD said #6 misfire.

I replaced the Cap, Rotor, Wires and Plugs a month prior to this issue. All plugs carefully gapped. When the OBD code was detected I went through the ignition system again to make sure everything was good.

Throttle body and IAC have been thoroughly cleaned and a good dose of SeaFoam has been run through the manifold.

Resetting the computer seems to make it run a bit better though there is a definite lack of power but the CEL comes back on after a few minutes.

At idle a miss can be detected. Removing the plug from #6 injector causes NO change. Removing plug from any other injector makes it run worse.

My thought is a bad or plugged injector. Is there a way to test an injector to be sure its doing its thing? Should I do a test on the plug to determine that its delivering proper voltage? Do I need to be looking at something else? If I can determine that this is just a bad injector I'll do the JY crawl for a set of 703s. BUT I don't want to get a set of new injectors and not fix the problem

thanks in advance

MtnHermit

Not likely to be the problem with your's, but I chased a misfire for 2-years before finding it was the wiring harness.
See this thread: https://www.cherokeeforum.com/f2/new...re-help-32066/

Zero cost to fix.

belvedere

You can swap the injector with another cyl. I bought my 98 Cherokee with a cyl 1 misfire. After eliminating all other possibilities, including making sure compression was in spec, I stumbled upon a TSB for misfires in (I think) 96-99 4.0s. If no other cause was found, the fix was to run a can of Mopar Combustion Chamber Cleaner according to the instructions in the TSB, and replace all the valve springs. I ran the cleaner and replaced just the springs on cyl 1, and the problem was cured.

Rev.LowBuck

Thanks Belvedere
I'll swap injectors around and see where that takes me. Will also check wires on #6 injector plug.
A link or source on the TSB would be helpful. Anyone?
I've read that a gasket failure can produce the same results. I can hear an exhaust leak on cold start, not sure if it is at the top or just the donut.
I bought this thing for my daughter to drive because I was told they run forever...it's acting like it will, though poorly.

tjwalker

Absolutely start with swapping the #6 injector with another.

That "swap and follow" technique is the perfect first step here.....

Rev.LowBuck

I've determined that I have an injector issue. Swapped 4 & 6 and now it changes (runs worse) when I take the plug off #6 and there's no change when I take the plug off#4.
So...please help me plot a course of action.
Here are the options as I see them in order of cost/hassle.
Get a single injector at the junk yard & hope it works.
Get an injector rehab kit & hope it works
Get a set of 703s either junk yard or forum vendor...and hope they work.
Buy a set of brand spankin new ones...
What would TJWalker do?

cruiser54

Contact Programbo here on CF and get a set of refurbished injectors from him.

tjwalker

Depends on the checkbook. Just like all decisions!!

Swapping isolated the problem as the injector itself. So if money is tight, you could pick up a few salvage yard injectors and hope you get a good one to install.

But if you plan on keeping the vehicle, I'd recommend a new set of 6 as if one injector is failing.....Murphy's law says that others are not far behind. And I always listen to Murphy. He has educated me well over the years.....

In which case you could get a set of rebuilt flow tested injectors from a company like Precision Injectors for a couple of hundred bucks.

I've heard of, but I'm not familiar with the 703 swap, so can't help you with that.

Brand new injectors (or reman) from a reputable company like rockauto.com is yet another option and a pretty good one I think (they have about 7 offerings for your 98 XJ). Stay away from the bottom end pricing stuff.

I just saw Cruiser's recommendation. I don't know Programbo, but trust Cruiser's recommendations so check that out too.....

Good luck! At least you have isolated the problem and you should be thankful for that!

Rev.LowBuck

Thanks cruiser54 and TJWalker,
I've been a bit frustrated by responses to other questins/posts on CF that were either off topic or posted by advisors who obviously knew less about the issue than me.
Your direct and seemingly accurate input is refreshing.
I pledge to return to this thread with my solutions so that future searchers (always search first!) will have some useful data.
Thanks again

belvedere

I've seen reman injectors on ebay for around $100/set. I haven't personally used them, but if I was in your shoes, I think I'd give them a try.

Rev.LowBuck

Here's the end of the story...
I took a chance on an ebay offering and bought 12 703s. 6 for my daughter's '98, 6 for my '93. soaked them overnight in injector cleaner and sprayed the heck out of them with carb cleaner. I didn't do the whole hook it to a battery and backflush thing...call me lazy.
Installed them in my daughter's '98 and BINGO! the thing runs like a champ. I may have had similar results with a complete cleaning of the injectors I took out of her Jeep (everything was scary dirty including the fuel rail) but I wanted to try the 703 swap after reading nothing but success stories.
I also swapped 703s into my 70,000 mile '93. I had a hard time getting it started, still not sure why but after many, many tries and letting it sit for a couple hours it finally fired up. The improvement is not as dramatic (again, the '98 was really dirty) but part throttle response is improved.
Ready for the improved MPG!