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another hard to start Renix..

mtbxj87

NAXJA Forum User
Location
Bend, OR
1989 4.0 aw4
Every sensor has been replaced and function ok. All grounds are upgraded. New alt and battery. Tune-up components ok. Fuel pressure ok. She runs and drives great. The only thing it takes too long to start. Ive done all the tips and tricks that can be done, I think..
My next thing is coil and ignition..?
Could a weak coil cause this?
 
Try turning the key to run, off, run off maybe three times then try a start. Sometimes the fuel check valve leaks and you need multiple primes to fill the fuel rail back up to pressure.

Coils in my experience don't get weak, but you can get a weak spark condition for various reasons. I usually grab and old plug open the gap to 0.060 hold the plug on a good ground and have somebody turn the motor over. You should hear the spark crack and it should blue/white. Make sure the ground on the plug is good and don't push your crotch against the fender while holding the plug and making this test.:)

Starts aren't usually the issue with weak spark, though it can happen in extreme cases. Usually the idle gets pretty bad way before you have starting issues.

Less of an issue with the 89, but the wiring between the CPS and the ECU can degrade the signal. The CPS only puts out around 0.5 volts (if you are lucky) and it doesn't take much resistance in the connectors or the wiring to degrade the voltage pulse to the ECU.

If you get weak spark, it is usually the spark plug wires or the coil to cap wires. Sometimes high resistance int he high voltage cables, sometimes moisture and you loose some spark before it gets to the plugs. *Sometimes a bad connection between the coil and the ignition module*. Sometimes low voltage to the ignition module from the ignition switch and/or a bad connector or splice somewhere between the ignition switch and the ignition module. A wet motor can lower the voltage to the ignition module also, tiny voltage leaks to ground though moisture somewhere along the way between the ignition switch and the ignition module can lower the voltage to the ignition module. The voltage to the ignition module is typically a volt or so lower than battery voltage anyway. due to resistance and line loss. But like I said, really poor idle is usually the first sign of ignition trouble, then the spark breaking down again at higher RPM's ()above 3500 or so). The ignition in the Renix is actually pretty good and hard to improve upon, bad wiring, poor connections or moisture where it shouldn't be is usually most of the trouble.
 
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I recently replaced the coil/ignition module because it had become sensitive to low voltage. The battery wasn't real good and when you cranked, it dropped to around 6 volts and the module would not reliably generate a spark. It worked fine with a new battery, but I replace both. The battery was still under warranty.
 
Thanks for the responses. Ill have to double check voltage at the coil at start up. I don't think it is supplied voltage though, I may be wrong. 8mud has me thinking though. ill have to keep a fuel pressure tester on it to see if pressure is bleeding down. Shop Key specs the fuel pressure to stay at least 19 psi in the rail with engine off.
Shes always done it but she'll start every time.
 
Thanks for the responses. Ill have to double check voltage at the coil at start up. I don't think it is supplied voltage though, I may be wrong. 8mud has me thinking though. ill have to keep a fuel pressure tester on it to see if pressure is bleeding down. Shop Key specs the fuel pressure to stay at least 19 psi in the rail with engine off.
Shes always done it but she'll start every time.

I've had low voltage to the ignition module for numerous reasons. Ignition switch meltdown from the brown wire circuit, line leak from splashing water all over the engine bay, battery with a bad cell and even from starter issues ( a starter that sucks way too much juice). Water is by far the most common for me. My hunting lease has some large puddles and I always think because I made it through the last time I'm going to make through this time. Sometimes the water in wiring issues don't show up until the next morning.

The check valve in my fuel system leaks, I've gotten used to turning the key from off to run a couple/few times before I start, Especially if the XJ has been sitting for a couple of days. I live with it as long as it doesn't get any worse.

The coil separates from the ignition module. The contacts under there get corroded, the old style were worse, the newer style can also cause issues. It is kind of a mud and trash trap where the coil contacts meet the module.
 
I just replaced the fuel pressure regulator on my '91 and now starts right up. I'm not sure about the renix, but on my HO the fuel pressure is 31 psi, but if you disconnect the regulator it should jump to 39 psi. It should also hold pressure after shut off. Mine was toast, would drop to 0 psi after shut down. Required a really long crank for the pump to rebuild pressure.
 
1989 4.0 aw4
Every sensor has been replaced and function ok. All grounds are upgraded. New alt and battery. Tune-up components ok. Fuel pressure ok. She runs and drives great. The only thing it takes too long to start. Ive done all the tips and tricks that can be done, I think..
My next thing is coil and ignition..?
Could a weak coil cause this?

Describe "too long".

Are you aware that longer than normal cranking times are normal with the Renix system?

Did you refresh the grounds at the dipstick tube stud?

Clean or bypass the c101 connector?

If it were me, I would click on the link below and do Tips 1 through 5 and possibly 27.

https://docs.google.com/file/d/0Bz4d205LaED2SUxMOGZnY3RjaEE/edit?pli=1
 
Yes Ive done all the Cruiser54 tips. My 89 does not have the c101 and sensor grounds are good. Turning the engine over for maybe 5 seconds at a time, usually starts on the second key over.
 
Yes Ive done all the Cruiser54 tips. My 89 does not have the c101 and sensor grounds are good. Turning the engine over for maybe 5 seconds at a time, usually starts on the second key over.

Why go 5 seconds and then again?

You may have a leaky injector that lets the fuel pressure drop in the rail while sitting.

Try the "poor man's prime".

Turn just to On for 10 seconds, then Start. If it's noticeably better, you're likely losing fuel pressure.

I tip on injectors for the Renix guys:
0 280 155 746 Volvo injectors are a wonderful replacement on our 4.0 Jeeps.
 
Similar issue with my RENIX, but less so. My procedure is to turn key to 'on', then listen for my fuel pump to kick in, and go silent before I turn key to 'start'. Even then, the engine turns over for a few beats, then there is a slight pause.., couple of more beats, then fires up just fine. I live with it. (lol).

Still.., I do wonder the cause, but I'll probably wait until next summer as it's frozen fingers time up here where I'm at, working outdoors, and all.

I really pay attention to the expertise given on this site, and for the first time I see a tip to use Volvo Injectors. FIrst time I've ever seen that tip. Cruiser54, is that a new first time post as per using them? I've seen Ford, Chrysler injectors mentioned before, besides OEM suggestions for the RENIX.

I am always amazed by Cruiser54, 8Mud, Old_Man, and a host of other's inputs, and you will too. I am glad that I became a paying member to help keep this site up.., just a thought.
 
Lots of info on the interwebs for XJ. so much from this site. But Ive search a lot to find my problem before I made another post about it. Obliviously haven't found my problem. My issue is more of an annoyance, im going to triple check the fuel. ive ran the pump multiple time before start. It isn't light and day difference but it helps a little. But like always I appreciate any positive advice
 
Lots of info on the interwebs for XJ. so much from this site. But Ive search a lot to find my problem before I made another post about it. Obliviously haven't found my problem. My issue is more of an annoyance, im going to triple check the fuel. ive ran the pump multiple time before start. It isn't light and day difference but it helps a little. But like always I appreciate any positive advice

Any difference between cold and hot starts?

You might want to check your CPS voltage. I usually get about the same results with an OHM test, the ohms get much over 150 and the ECU can miss a few pulses during cranking. 175 ohms or more an starts can get really iffy. The ohms can change depending on temperature.

A slow starter can also mess with your starts. I've heard the Renix has to be cranking a certain RPM to get a start, not sure of the RPM or maybe it just takes a certain number of pulses from the CPS? I've noticed when I've let my battery run down, starts can take a long time.

Does it ever miss shortly after a start and then stabilize? This can be a sign the CPS may be missing a few pulses. Best guess is the CPS-ECU program likely adapts to a few missed pulses, but has it's limits. A few too many missed pulses and you get a miss or an iffy start. Like I said, just a guess, but observation seems to support my guess.

Try a volt test at the larger yellow wire at the ignition coil, while it's cranking over. The starter can suck the voltage way down. It isn't set in stone, but voltage down to around 9 volts and the spark is good enough, if it gets down to around 6 volts starts can get iffy, especially in cold weather.

I ran an ohm test on my CPS wiring to the ECU connector and had substantial resistance. I fiddled with it for most of a day. The next day I gave up and chopped the CPS wires from the ECU about 2-3 inches inside the engine bay and ran the CPS pigtail straight to my shortened wires. Jeep used to have a kit, that did about the same thing. I just relocated the connector from the harness and bypassed a bunch of wiring. I soldered and heat shrank the splice.

Like Cruiser said the Renix typically needs a long crank to start compared to some other cars, even the later HO models start quicker. Mine typically takes a slow two count maybe a fast three count to start on a warm motor.

If turning the key back to off and then to run again to get some addition prime doesn't help, it is likely to be a CPS pulse issue (CPS or wiring) or as you suggested weak spark.

My 88 pops right over, unless I've let it sit to long and it's lost a little too much prime pressure/fuel volume in the fuel rail.

For bragging rights, I let my 88 sit for almost a year. I ran the pump for awhile to purge the old fuel out of the fuel rail and the fuel lines and it popped right over first try, 2-3 seconds of cranking. I tossed the carbon core plug wires a long time ago and replaced them with solid core coil wires, I kept the stock carbon core ignition coil to cap wire, it seemed to run better that way. The new wires really helped my idle and my starts. Mine idles a little low (500 RPM), but thumps like a champ and never misses a beat.
 
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When she fires up she is running great, no spudder or miss. And when fire she barks to life really well, it sounds great with custom exhaust on her. BRAAAPPP grrrrr idle.. It just takes a some cranking to get there. Cps is ok .55volts while cranking. Tried both sensors I have and did Cruisers mod to get it closer to the flex plate. Hot/ cold it about the same time. Are my expectations too high? As a technician, its a little frustrating.
 
Similar issue with my RENIX, but less so. My procedure is to turn key to 'on', then listen for my fuel pump to kick in, and go silent before I turn key to 'start'. Even then, the engine turns over for a few beats, then there is a slight pause.., couple of more beats, then fires up just fine. I live with it. (lol).

Still.., I do wonder the cause, but I'll probably wait until next summer as it's frozen fingers time up here where I'm at, working outdoors, and all.

I really pay attention to the expertise given on this site, and for the first time I see a tip to use Volvo Injectors. FIrst time I've ever seen that tip. Cruiser54, is that a new first time post as per using them? I've seen Ford, Chrysler injectors mentioned before, besides OEM suggestions for the RENIX.

I am always amazed by Cruiser54, 8Mud, Old_Man, and a host of other's inputs, and you will too. I am glad that I became a paying member to help keep this site up.., just a thought.

Guys on Cherokee forum have been using the Volvo injectors for over a yer.

I've used others on 3 rigs but was impressed with the 746s I installed on my neighbor's Jeep.

Here's a link to Renix Tips as hosted on NAXJA.

http://www.naxja.org/forum/showthread.php?t=1115935
 
When she fires up she is running great, no spudder or miss. And when fire she barks to life really well, it sounds great with custom exhaust on her. BRAAAPPP grrrrr idle.. It just takes a some cranking to get there. Cps is ok .55volts while cranking. Tried both sensors I have and did Cruisers mod to get it closer to the flex plate. Hot/ cold it about the same time. Are my expectations too high? As a technician, its a little frustrating.

Your expectations are high.

As Service Manager and Shop Foreman at a Jeep dealer from 1980 through 1992, how do you think I felt telling Renix 4.0 customers that the cranking time was normal? It sucked!!
 
Your expectations are high."


Sigh...
Anyway, about these injectors.. Ive never replaced mine so I am interested. Are they for performance gains? ive been getting 22-23 highway mpg (much worse in town). im happy with power so not really into trying to get more, I wouldn't sacrifice mileage.
 
LOL, but that might get it started on cold start :)

"Make sure the ground on the plug is good and don't push your crotch against the fender while holding the plug and making this test"

I am working on a somewaht new to me renix 87(IIRC? or 89, I forget LOL) no power or low voltage to the fuel pump right now. Looking for your old posts and jpgs on the wiring for renix Fuel pump. I have 12-13 volts at and across a good ballast resistor, and I hear the timer relay and feel the fuel pump relay cycling. Ground wire harness at the fuel pump is good, but one wire is dead, one has about 4 volts (level sensor?) and the third is ground at the harness to fuel pump weather pack connector (tested while disconnected). I need to check for varmit wire damage as the Jeep has been out of service while I was ill (it ran when I bought it 18 months ago).

I have a great hot spark and it cranks, battery is new....
 
sorry just saw this, did you get it fixed? the resister should have 12v one side then the pump side should be 8v or so.
 
Just a follow up. After I replaced the distributor it fires up pretty much right away. the pickup in the dizzy was a little corroded and I imagine getting a weak signal. Also, I indexed the new dizzy. It wasn't too far off anyway tho.
 
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