Hard Start/No start and high idle...Help please!

[MaxxTraxx]

History: 1989 XJ 4L, AW4 175xxx. I recently bought it from a friends family, it sat for a year before I bought it. I jumped it off with my buddies XJ and it fired right up, the more I drove it the better it ran, drove, stopped, etc. This was about 2 months ago today.

I have replaced the battery, and have done a full tune up and a new fuel filter in the time I have owned it.

It seems hard to start, requiring almost double the time to fire than my 93 XJ. The starter spins the engine over easily, it just seems to not be getting any spark. Sometimes it will start and sometimes it wont start. So, last Thursday I replaced the cap, rotor, plugs, wires and did a 3-step kit from berrymans/chemtool. I used auto zone ignition parts, and oem spec champion plugs, nothing fancy. I thought that would cure my hard to start/no start issues and the 3-step would straighten out my high idle issue, but it has not.

The jeep would not start yesterday or today...just spins the engine over. It ran fine Saturday, Friday, Thursday, Wednesday of last week. Sat. afternoon was the last time it ran.

I put a fuel psi gauge on the rail a week ago and got 40psi with the key cycled to ON. I am thinking it is a CPS issue, but I do not want to just throw money at it in hopes of fixing it. I am waiting on a friend to come over with a multi-meter so we can test the TPS and the CPS but I am hoping someone on here can give me some advice. I'm kinda lost as to what would keep it from running at this point.

[pvt.tadpolxj]

Here is a good place to start. These Ign coil's are notorius for failing depending on where you buy them. I was buying them at Auto zone, and i kept having trouble with them. My mechanic recommended buying them from Napa. But you might try relocating it to the nearest fender. this will help keep all of that heat off that come's from the engine block.The heat causes them to fail......:thumbsup:

[MaxxTraxx]

I have not replaced the ign. coil....I'll have to look up how to test it. Thanks Pvt. Tadpol xj.

[pvt.tadpolxj]

If it's a few year's old, or very dirty from being mounted next to the engine block. You can bet it's the Ign coil. They run around 25.00ea. Keep in touch on this..:driving:

[JENSSEN]

What the fuel pressure at when its trying to start,..?

[4.3LXJ]

The reason there is a difference between the two rigs is that one is a Renix and the other is an OBDI. The OBDI will start to fire and squirt fuel as soon as the flywheel notifies the ECM #1 has passed the CPS. Your Renix needs to verify 300 rpms for three revolutions at proper fuel pressure before it will fire.

[MaxxTraxx]

I put a fuel psi gauge on it a week ago and it read 40psi when I cycled the key on. I didn't test it further than that. I work at a auto repair shop, but the techs there don't really want to work on my jeep b/c it is so old....they don't want to do a lot of freebie work.

So, b/c the computer needs to read 300rpm 3 times to fire, does that point to a CPS issue or a fuel supply issue? I am going to check the ignition coil out tomorrow when I get off work at 4 and either replace it or rule it out as working properly.

[bigjim350]

Sounds like maybe a cps. When it is idleing high does the intake make a loud air sucking sound.. If it does it could be a IAC sticking open, or sometimes they get out of sync when jump started.

[steph74]

The reason there is a difference between the two rigs is that one is a Renix and the other is an OBDI. The OBDI will start to fire and squirt fuel as soon as the flywheel notifies the ECM #1 has passed the CPS. Your Renix needs to verify 300 rpms for three revolutions at proper fuel pressure before it will fire.


What he just said Rennix engine have a long long long crank.... and 89 should still have at he rennix unless it has been replaced by a new system

You may want to check the IAC for the high idling..... it is the Idle air controller... sometimes it get stuck when dirty and provoke high idle..... easy to check and clean just to make sure.... they are pricey little pieces to replace but last time I hit the junk yard I collected all I could find and got 5 for $8.... I tried all of them until I found one that was working fine.... (what wouldn't I do to save money ;))

For the no start issue, just make sure also all your connectors are grounded properly, especially the pesky little ground cable from Block engine to firewall....

[steph74]

Sounds like maybe a cps. When it is idleing high does the intake make a loud air sucking sound.. If it does it could be a IAC sticking open, or sometimes they get out of sync when jump started.


And if CPS or TPS turn out OK then check your vacuum lines you might have a leak somewhere that could explain the high idle

[MaxxTraxx]

I put a new IAC and it made it idle higher....1100ish in D 2100 in P vs. normal idle in D and 1500ish in P or N. All the vacume lines look new and in good shape. no whistle sounds at idle, intake is tight.

[steph74]

I put a new IAC and it made it idle higher....1100ish in D 2100 in P vs. normal idle in D and 1500ish in P or N. All the vacume lines look new and in good shape. no whistle sounds at idle, intake is tight.

dang....
(did you reset the computer by any chance ? just checking but sometimes it can help lol)

next step is definitely checking TPS then

I know there are some Rennix Guru on this forum I am sure they will come to the rescue ;)

[BlueXJ]

Your Renix needs to verify 300 rpms for three revolutions at proper fuel pressure before it will fire. As stated by 4.3:XJ is correct and it is the ECU that is looking for that signal before allowing the ignition to be turned on, so it can not be altered.

[pvt.tadpolxj]

Take some good advice my friend get a new Ign. Coil... you are going to need it anyway......:driving::driving::driving:

[MaxxTraxx]

ok, new CPS in and it runs again.... :)

I have installed a new ign. coil, cap/rotor, plugs, wires and a CPS.

Now the jeep is running, but it still has a high idle. I tried adjusting the TPS both up and down, no noticeable change.

[pvt.tadpolxj]

Glad you got the Ign. coil.. most of the starting or running issue's on my Jeep are related to my Ign. coil, and my Nuetral safety switch..:driving::driving::driving::driving:

[MaxxTraxx]

I'll disconnect the battery tomorrow and hope that resets the computer and makes it idle normal again...I sprayed all the vacuum lines, TB area down with carb cleaner and no noticeable change n how the engine was running...leads me to believe I have no vacuum leaks.

As soon as I shift from P or N into a forward or reverse gear the idle instantly drops down to 900-100 rpm...1800ish rpm in P or N. TPS or IAC cause an excessive high idle?

What about the throttle stop on the TB itself?

[steph74]

I have a manual so the issues may be different... did you check that the butterfly of the throttle closes properly ?

[MaxxTraxx]

I haven't yet, Ill check the butterfly tomorrow.

[pvt.tadpolxj]

Hey MaxxTraxx. Man I wish I could tell you the answer on the high Idle at start-up. Mine act's the exactly like that, and I have been trying to figure it out for abou a year. And I have replaced all of the same sensor's. I believe it is a wiring issue somewhere on mine. But here is what I do that help's a lot. everytime I start mine I begin in Park, I allow the engine to crank about 4 or 5 time's. Then I move the shifter down to Nuetral, and wiggle it forward and backward in the nuetral spot several time's. I"m not sure what this is helping but when it start's it is at a good lower RPM.. I hope this can help...:confused::confused::confused:

[steph74]

Oh I need to figure out where is that thread/forum I had bookmarked...... 30 pages of discussion with a guy that was trying to track down his high idle problem. lots of valuable advices in it
I'll check on other computers...

[MaxxTraxx]

Steph74, did you ever find that other thread? I still have a high idle issue and am tottaly out of ideas other than a new TB.

[Mud junkie]

How does it shift? And have you checked for vacum leaks around the egr unit. As far as a rough idle , I have seen the TPS cuase a hard start , rough idle and shifting issues on the renix system.

[MaxxTraxx]

I forgot to update the post...jeep is fixed, runs great.

[Mudderoy]

I forgot to update the post...jeep is fixed, runs great.

Come on what was the solution! :cry:

[4x4Dalton]

X2 :poke:

[88AMCOMANCHE]

My MJ Renix has once or twice Idled up around 2k rpm & stays there upon startup. so I wonder why also.