misfire on renix 4.0 on hot startup

[Tito_73*]

Ok I'm back after a 5 day break. I guess this is some info for bcmaxx since you have the same issue. I cleaned my t-body, removed my idle stepper motor cleaned the pintle and cleaned the orifice that the pintle seats in. I got a much better idle now, but sadly I still have the hot-start miss. I purchased the non contact thermometer. I was checking my underhood temp with a hot engine my block seemed normal around 210. I started checking the fuel rail, then each injector. All were the same except for #2, don't remember the temp, but I could touch #1 with my finger and I was ok. But when I touched #2 ouch, hot. Then I started it up, misfire, disconnected #2's connecter, no change in rpm found suspect cylinder. I connected a spare injector and felt it clicking, circuit is ok. It finally dawned on me bad injector right, wrong. I had been here once before. I then realized one of these things is not like the other. #2 did not have the retaining clip holding the injector to the fuel rail. So when the rail was pressurized it bottomed out the injector causing the body to contact the intake, resulting in the injector getting to hot when I shut off the engine. I need to confirm this by going to the local junk yard and getting a clip. I will let you know if this fixes it, maybe then I will be worth the :worship: emoticon

 

[Ecomike]

I bought a new set of those clips for mine at Autozone for a couple of bucks.

Sounds like your homing in on the problem there, I found an extra extraneous o'ring in the fuel rail on mine causing sealing problems once! Just in case your problem persists, check that wiring harness, all the sensor the grounds through the harness, and the main grounds for a loose temperature sensitive ground connection in any of them!

Also did you replace the TPS, is it new? If not it could be displaying a temperature sensitive bad idle spot that is very hard to detect or prove except with a high impedence analog meter, or replacement.

These suggestions apply to all you guys fighting a similar problem.

Just keep the faith, I know that Renix engines can run smoothly all the time once you zap all the gremlins, even an old tired one with 249,000 miles on it, just ask me how I know!:sunshine:

 

[bcmaxx]

I bought a new set of those clips for mine at Autozone for a couple of bucks.

Sounds like your homing in on the problem there, I found an extra extraneous o'ring in the fuel rail on mine causing sealing problems once! Just in case your problem persists, check that wiring harness, all the sensor the grounds through the harness, and the main grounds for a loose temperature sensitive ground connection in any of them!

Also did you replace the TPS, is it new? If not it could be displaying a temperature sensitive bad idle spot that is very hard to detect or prove except with a high impedence analog meter, or replacement.

These suggestions apply to all you guys fighting a similar problem.

Just keep the faith, I know that Renix engines can run smoothly all the time once you zap all the gremlins, even an old tired one with 249,000 miles on it, just ask me how I know!:sunshine:

I've replaced all 6 injectors with clips in this evil battle among many other things.And also a tps. Mine runs completely tip top and awesome all the time except for the misfire b.s.
I'm at the point where there isn't anything elso to change but hard engine parts. I've kinda leard to ,live with the miss. Just don't shut it down when you make brief stops (dog on guard) and when I do it cools off enough to not miss when I start it back up.
Though it would be more than cool to know exactly what causes this.

 

[CheapXJ]

coolant temp sensor on the block.

the renix is receiving no input from that sensor. it's running as if it's cold because the ECU will default to cold startup program. there's a predetermined window, I forget if it's time or revolutions on the counter.

 

[bcmaxx]

coolant temp sensor on the block.

the renix is receiving no input from that sensor. it's running as if it's cold because the ECU will default to cold startup program. there's a predetermined window, I forget if it's time or revolutions on the counter.

wouldn't that be something!! I will install one tonight, I thought that was for the gaugel I replaced the one on the block thinking that was the ecm one. tito I'll post up on my findings,how'd you make out on the f/i clips?

 

[89xj]

wouldn't that be something!! I will install one tonight, I thought that was for the gaugel I replaced the one on the block thinking that was the ecm one. tito I'll post up on my findings,how'd you make out on the f/i clips?

temp sensors for the renix:

back of head is for gauges
side of block is for computer
side of radiator is for aux fan

 

[Ecomike]

The ECU CTS is near the oil pan, lower block, drivers side on the Renix. IIRC I ran mine for over a year with the CTS disconnected and never had this missfire issue when hot.

How about a valve that stops sealing completely only on the hot restart that seals on a hot running engine and a cold engine, thinking diferential temperatures on the head & valve? In other words a valve that is giving early warning signs of pending valve problems?

Have you tried checking compression 5 minutes after a hot engine shut down?

Personally I would still look at the wiring harness. Someone here had a broken wire in a sensor line that made contact in the wiring harness intermitently, that was temperature sensitive on the sensor contact. Also check the sensor connectors themselves for temperature sensitivity. I finally had to run a seperate, new ground wire for my TPS on mine and a new 5 volt wire to my TPS to solve annomalies in my wiring harness.

 

[CrawlingCritter]

Have you added any extraneous electric/electrical aftermarket add-ons? And like tied into one of the Renix relays on the passenger side near the large ignition relay? The Renix ECU can get flaky if one of its I/O lines is compromised. If the misfire happens with your foot on the pedal you may have a bad TPS. I know--a lot of help this is...

 

[Tito_73*]

Well I am back I guess this thread is still going strong. I went to the junkyard today and got a couple of spare clips man there are nothing but renix xj's (no h.o.'s) in the boneyard, mine won't be going there though. I put the clip on and drove home. I parked my xj in my back yard and did the usual test let it sit for a couple of minutes and then the restart. No miss, this time I think I got it. I will post again after about a week of continued hot starts. Well sorry to hear that you still have the miss even with the clips bcmaxx, I would say good luck but even I know this doesn't magically fix problems. As far as the sensors go all I can say is that e.f.i. has the capability to compensate for many conditions, like a disconneted cts sensor, a default to open loop which results in a rich mixture. Which in theory should be easier to ignite than a lean mixture. I checked all of my sensor parameters when the miss occured with my scanner (mt2500) and everything was normal, thats when I knew it was related to heat and after pinpointing the cylinder I noticed the difference in heat between the neighboring injectors. I know electrical components hate heat (just like auto-tranny's) case in point the injector. Well I hope I finally got it, I will post and let you all know soon.

 

[old_man]

A misfire after a hot soak sounds like an overheated injector. There was a TSB for this on the later models.

 

[Tito_73*]

okay a follow up on old man's post. There is a tsb for the 99-04 4.0 engines used in the grand cherokee's. I found the tsb#1803103 and the link to view it [URL="http://www.wjjeeps.com/tsb_list.htm#1803103"]www.wjjeeps.com/tsb_list.htm#1803103[/URL] hope this helps

 

[bcmaxx]

My problem is no more, I did two things that may have made a difference:

replaced complete longblock assembly, and covered the intake heat sheild with cool tape. which one fixed it I'll never know. :dunno: I'm leaning towards the lifter. hurrayparty1: problem solved.

 

[outlander]

Thats one way to fix a problem......

 

[bcmaxx]

My problem is no more, I did two things that may have made a difference:

replaced complete longblock assembly, and covered the intake heat sheild with cool tape. which one fixed it I'll never know. :dunno: I'm leaning towards the lifter. hurrayparty1: problem solved.

I am sad to report the problem still exists, (insert expletive here!!!!). I'm thinking fuel injector. Either boiling and vapor locking or an injector bleeding down, smells quite rich after I start it and the rough running. I had installed reman injectors about a year ago. They were to fit a 93 5.0 truck engine. I want to put new injectors in. Is there a better year /application that will work better?

 

[Ecomike]

I would not waste my time with anything other than new injectors, and the good ones at that. Used ones (unknowns) can ruin a good engine way too fast too be worth messing with, IMHO. Got mine for a fraction of the cost of dealer and most parts store prices at

www.fiveomotorsports.com

I think it was these:

http://www.fiveomotorsport.com/PartsJPEGs/Injectors/d5b_takeouts_6.jpg

Original Equipment Replacement Upgrade
Ford/Bosch
4-hole Disc Type
Brand NEW sets
Jeep 1987-95 4.0

http://www.fiveomotorsport.com/Injector_SetsJEEP.asp

I am sad to report the problem still exists, (insert expletive here!!!!). I'm thinking fuel injector. Either boiling and vapor locking or an injector bleeding down, smells quite rich after I start it and the rough running. I had installed reman injectors about a year ago. They were to fit a 93 5.0 truck engine. I want to put new injectors in. Is there a better year /application that will work better?

 

[MJmk]

EGR??

Seems like I remember that the Renix systems that have a transducer (that black disk thing) in the egr vacuum system can cause a misfire/rough running condition like you describe. The transducer starts going bad, and causes the valve to open too much, causing the miss. I know my '87 doesn't use it, but I believe the 88-90's do. And way back when, you had to buy a new egr valve to get the transducer since it wasn't sold separately.

Disclaimer: It's been a while, and I'm getting old so hopefully this is correct At least it's an easy check! IIRC just plug the vacuum line at the egr valve and see if the miss goes away.

 

[bcmaxx]

Fuel pump went last night, happened to have a new spare in my trail box, so far so good. It slowly lost power and would only run at full throttle.

 

[bcmaxx]

What might cause the rubber fuel line from the pump to bracket to swell up? The hose was soft too. Tank and pump were replaced not much more than a year ago? crap ethanol gas?

 

[Ecomike]

What might cause the rubber fuel line from the pump to bracket to swell up? The hose was soft too. Tank and pump were replaced not much more than a year ago? crap ethanol gas?

The wrong rubber type in the hose, i.e. the wrong hose type, needs to be fuel injector hose good to at least, or rated for at least 50 psi. Vacuum or vent, or windshield washer hose or coolant hose is not suitable.

 

[bcmaxx]

It was the formed hose that came with the pump, just swelled up