Renix starting problems.

So lately my jeep is struggling with life. I have a 89 4.0L and lately sometimes when i go out and start it, it will start and rev up to a little under 1,000 rpm, then drop back down to 200 fast, and then work its way up to 750-800ish.... usually it will start and then rev up to 1800 and drop down to 1,000 and then gradually down to 800. Sometimes it will work normal... and sometimes it has issues. My jeep doesn't idle very well... at all.. its very jumpy and it misses. And its been that way for a while. The jeep idles much better when its warm, but its still pretty jumpy with the occasional miss. My TPS is adjusted to .085ish volts. I have new injectors. I have a brand new CPS, IAC, and Knock sensor. My gas milage sucks too... My O2 sensor was replaced just before i bought it in 2009. Please help.

Get a new relay Bosch relay. Look in engine bay on the passenger side you will see 4 relays in a row. I can not remember exactly which one but in the book it is listed as a "+B Latch relay". This relay actually works with your IAC motor. I was having the same issue you where and when it idled to about 1800 I would tap the relay HARD and it work idle right after that till the relay got stuck again....I eventually got a new relay and have never had the issue again in either of my 2 89's

With the engine running,spray around where the intake manifold meets the head, using throttle body cleaner. You could have a vacuum leak there. Also make sure all those plastic CCV tubes and their grommets/rubber connections are not cracked, split, melted, or clogged, etc.

Thanks for the replies. I have checked for vac leaks several times, and i know it doesn't have a vac leak. I have switched around my relays and it doesn't seem to make a difference either.

check out this site if you don't know of it yet. Some good info about the sensors on the Renix era
http://www.lunghd.com/Tech_Articles/Engine/Basic_Sensors_Diagnostics.htm

TEST your way to the answer--visit lunghd.com as suggested earlier.

What INJECTORS are you running? OEM single-pintle fire starters or late model 4-hole disc injectors? Read about fireproofing the 4.0: http://www.jpmagazine.com/techarticles/engine/154_0811_preventing_jeep_engine_fires/index.html

With o2 sensors its not the AGE but the MILEAGE--60k on a Renix sensor.

A**uming the plugs, cap (brass contacts, not alloy), rotor, and plug wires are recent, what are the plug gaps set at and are you torquing the plugs to spec?

What condition are your grounds? Head to firewall POS braided strap should be replaced with a 4 or 2 gauge cable. DIPSTICK--no, not an insult--there are CRITICAL grounds at the dipstick tube--ECU, ICM/coil, o2 sensor, others. ALL GROUNDS must be cleaned to bare metal, the metal treated with an anti-corrosion agent, and made TIGHT. (What is it Tupperware and walruses have in common--they both want a tight seal.)

When was the last time you removed the IAC and cleaned the throttle body and the IAC port with a TB safe aerosol cleaner, cotton swaps, and a toothbrush?

Remove the ICM from the coil, clean the clips/contacts, and treat them with dielectric grease.

What was your REFERENCE voltage at the TPS? The OUTPUT voltage--the number you adjust the TPS too, needs to be 17 percent of REFERENCE voltage for a manual trans and 83 percent of reference voltage (on the transmission side of the TPS) for an auto trans.

That should keep you busy for a little while.

There Joe goes again-muddying up the waters with logic, first-hand experience, and details............Been busy with the new shop lately, Joe? Haven't seen as many posts lately.

cruiser54 said:

There Joe goes again-muddying up the waters with logic, first-hand experience, and details............Been busy with the new shop lately, Joe? Haven't seen as many posts lately.

Click to expand...

Yeah, moving stuff out of storage, buying new-to-me shop stuff and working like a dog. Son hasn't given up his day job yet, he needs to finish his dental repairs before giving up his insurance. Days are running about 16 hours on average--at my age I should be sleeping a lot more.

Were busting the nut and putting away some, so cash flow is covered for the next 3 months or so. I hated starting a business on a shoestring years ago, and here I am doing it again.

The truth is its fun working with my Son--haven't spent this much time together in YEARS!!

PS--I'm a wrench slut and will work on about anything for money. Just got back from a roadside no start on a KW cab-over.

You work on big rigs, too? I did roadside service and heavy duty towing/recovery for years. I'm sending you a PM.

Thanks for the reply!

Well i guess i should give a little background on my cherokee. It only has 10,000 miles on the rebuilt motor... but i had the problem even before i rebuilt it. The injectors are neon 703's that have new filters, and have been properly cleaned in a ultrasonic cleaner. I put new wires, plugs (properly gapped), rotor, and cap on when i rebuilt the motor. Also the throttle body and intake manifold were cleaned in a solvent tank when i rebuilt the motor. So they are thoroughly cleaned inside and out. The grounds (both on engine and firewall) were cleaned with a wire brush, and the neg cable is new. Also when i rebuilt the jeep i took the entire wiring harness out and cleaned it, and applied dielectric grease on all connections. Today i checked my reference voltage and its around 4.8 volts on the tps, so i adjusted the tps to .82, and it fixed the startup issue, but the jumpy idle especially when cold is still very much there. Also for the past couple of weeks my tach has been glitchy. What could be causing that?

I have tested the MAT and CTS, and they appear to be good. I swapped out the MAP sensor from another jeep to see if it would make a difference, and it didn't, so i am thinking the MAP sensor isn't causing the issue. I checked the resistance for the heater in the O2 sensor, and it was around 8.8 ohms if i remember right. There should only be 25,000 miles or so on that O2 sensor, but thats not to say it isn't bad.

I haven't even messed with the coil or ICM, thats one of the few things i didn't replace when i rebuilt the jeep. so maybe ill try that next. Is there a way to test the coil/ICM?

As Joe stated, remove the coil from the ICM and clean the contacts.

Just to be clear- have you scraped the paint from your new block at the dipstick tube stud and polished the terminals on the wires? Those are super-important grounds.

I actually put in a bolt in before i painted it, because i knew the grounds hooked up there, so its bare shiny metal on the block where the grounds go. I cleaned the connections, but i'm going to go and re clean them with a wire brush, just so i can completely rule out the grounds. Ill also remove the coil from the icm and clean those contacts as well. Ill post my results when i get them. Thanks

You've done an excellent job so far. Keep up the good work.

So i went out and cleaned the ICM/coil clips, and i polished up all grounds and connections. After i rechecked the TPS voltage and its still the same. I also did a power balance, and it didn't show any irregularities. My jeep starting acting up again where when it starts it will now rev up to 500 rpm, and fall flat on its face, then gradually return to idle. Its intermittent, it only happens half of the time. The idle is still pretty jumpy, and my tach is still glitchy for some reason. Help.

I would pull the iac and clean out the housing with carb cleaner and qtips, then take a tooth brush and carb cleaner to the iac pintle.

My XJ has done this since I got it
I'm going to try all the pre-mentioned tests.
I wonder if the OP ever fixed this issue