Timing issue?

Well I am at wits end. 95 YJ, 4.0, manual. Will start and idle. After a short time, idle gets ruff. Try and drive it, forget it. Stalls. Has intake backfire. While running, accelerating does nothing. Replaced the fuel filter and map sensor. At the begining of June, went wheeling and hit some deep water. Water probably was sprayed all over the engine via the fan. It feels like a timing problem. Any guesses? Any info would be appreciated.

Greg Ginn

95 YJ, 4" BDS, locked, 4.10s, 33's

Pop the distributor cap and see if there is water/oil/crud in the bottom of the distributor, and if you have any carbon traces, replace the cap and rotor. Check the plugs too, you might have cracked one.

A weak coil can do this. If yours is original I'd replace it. They had a few changes to the design so take the old coil with you. I used NAPA part# IC409 (it's a kit with coil and a new resistor harness/adapter)

It could also be the CPS sensor (camshaft position sensor). But wait on that till you check the other things. Usually the CPS will simply cause the jeep to stall on deceleration or just not start at all.

evbeergoggles.com

Thank you, will look at that stuff tomorrow.

Greg

Thank you, will look at that stuff tomorrow.

Greg

** Posted from **

The other thing to check after a water crossing is the CAT. Thermal shock can shatter the core. Hit it with a mallet and listen for any loose rattling stuff.

Good point. If the cat is plugging the exhaust it sure will take the guts out of the engine.

To check for this, get a vac gauge and attach it to the intake rail. T off one of the feeds. Start the engine and you should see about

12-15 inches of mercury. Watch the needle if it drops down low or to zero once the engine is started and broght to a high idle, then you know the exhaust is plugged up.

Nice little site.

I had the cat replaced last summer. It rattled quite a bit when it was bad, and I knew that it needed to be replaced. Today I put in new coil, plugs, and cap. It had a new fuel filter and map sensor this week also. Running much better, but when I put my foot in it at cruising speed, I still get some minor surging, and intake backfiring. While at speed, I can depress the clutch, and it revs up fine. It seems that under load is the problem.

Greg

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Greg, since you went swimming with it you should also unplug the CPS and clean/dry that plug as well. A little dielectric grease around the seal gasket when you plug it back together helps as well. Same operation for the TPS connector while you're there wouldn't hurt. Mine is like a cat - gets a little persnickity when she gets wet.

Hmm.. load related problems are timing/fuel/ and spark. Intake backfire can be several things including sticky lifters and valve seats. Next suggestion is to do a compression test.

Did you pick up a tank of crapoline? or water?

Sometimes a tank of utter crap can plug more than one fuel filter.

Well since I have given it a tune up, ran the gas down and refilled, the problem has gotten ALOT better. So I may lean towards maybe getting yet another fuel filter. If I had some crappy gas, would it idle ok, and stumble under load? When I rev it up in the drive way, it revs no problem, and holds whatever rpm I give it. If it were timing wouldn't it stumble during that proccess as well. Baffled. Thanks all who have given me info. I really appreciate it.

Greg T

There are a couple of things that can plug up the filter. One tank of bad gas, or a lot of buildup in the tank that is freed by a fuel system cleaner or high detergent gas. Usually it's the diesels that get mold buildup in the tank. At any rate, a clogging filter can act as a choke point in the system. Low flow and it's fine, high flow and it acts like a kink in a hose. That lowers the fuel available and causes the engine to run lean. A lean run causes backfire, poor power, stumbling.

The other thing that can cause problems at higher RPM is a dying coil.

Simple check for the filter is to take it off, shake it, and drain the input side into a glass. You will be able to tell fairly quick if it's full of crud.

Thanks Doug.

Greg

my bet is that you have a bad front 02 sensor.

cold start it runs an enriched F/A ratio but as the water temp starts to increase the ECM will check the O2 sensor and start the transition to closed loop f/a control. a bad sensor will make it run lean with stalling, poor power etc.

my daughter's '99 TJ acted like this and baffled a local mechanic. didn't throw a code.

in addition to the symptoms you describe, when it was running rough and almost stalling ... going to WOT it would pull fine. but back at part throttle the same rough running.

i replace the front O2 sensor et voila

reboot

The sensor on the exhaust pipe? How did you get it out? My 93 YJ's is corroded solid.....

Extra lucky in that there were threads left in the hole - my luck runs such that I would have finally gotten it to turn and wound up with a smooth bore. Such SOBs usually come out best with an impact wrench.