Long crank times only when hot.

[Renegade XJ]

Hey guys I got a '89 Renix 4.0 that's having a long crank time issue. I initially thought it would be the fuel pump so I picked up a complete pump and sending unit, fuel filter, and a fuel pressure regulator. None of this has been installed yet, but I have started noticing that my long crank time issue is only when hot. In the mornings or after sitting a long time, it starts right up.... But if I go into a store and come back out an hour later I get a really long crank time. It sputters a bit at first but no back fire. Any thoughts before I start wrenching on this thing?

 

[cruiser54]

How old is the tuneup hardware? This sounds opposite of a fuel delivery problem to me. Sure couldn't hurt to replace the fuel filter as it is a maintenance item every 30,000 miles just as the plugs, wires, cap and rotor. Ever clean your throttle body?

Stick or auto trans? CPS output could be hindered by clutch material stuck on it if it's a stick. CPSs are also temperature sensitive. Easy to check with a meter both cold and hot. Here's how:

Renix CPS Testing and Adjusting
　
　
Renix CPSs have to put out a strong enough signal to the ECU so that it will provide spark.
Most tests for the CPS suggest checking it for an ohms value. This is unreliable and can cause some wasted time and aggravation in your diagnosis of a no-start issue as the CPS will test good when in fact it is bad.
The problem with the ohms test is you can have the correct amount of resistance through the CPS but it isn’t generating enough voltage to trigger the ECU to provide spark.
Unplug the harness connector from the CPS. Using your voltmeter set on AC volts and probing both wires in the connector going to the CPS, crank the engine over. It won’t start with the CPS disconnected.
You should get a reading of .5 AC volts.
If you are down in the .35 AC volts range or lower on your meter reading, you can have intermittent crank/no-start conditions from your Renix Jeep. Some NEW CPSs (from the big box parts stores) have registered only .2 AC volts while reading the proper resistance!! That’s a definite no-start condition. Best to buy your CPS from Napa or the dealer.
Sometimes on a manual transmission equipped Renix Jeep there is an accumulation of debris on the tip of the CPS. It’s worn off clutch material and since the CPS is a magnet, the metal sticks to the tip of the CPS causing a reduced voltage signal. You MAY get by with cleaning the tip of the CPS off.
A little trick for increasing the output of your CPS is to drill out the upper mounting hole, or slot it so the CPS bracket rests on the bell housing when pushed down. Then, when mounting it, hold the CPS down as close to the flywheel as you can while tightening the bolts.

　
　
Revised 07-30-2012

 

[Renegade XJ]

It's an automatic, a full tune up was done less than 10k miles ago. I'll check the CPS this weekend. I still might have an issue with fuel dilivery though, I put a fuel pressure gauge on it and the second I shut off the engine I lose all pressure really fast. Looks like the check valve in the pump isn't working.

 

[cruiser54]

Check the fuel pressure at idle. Should be 31 psi. Unplug the vac hose from the pressure regulator and it should jump to 39 psi.

 

[Renegade XJ]

Yea, fuel pressure at idle is 31/32. I haven't played with the regulator yet. I'm gonna start tinkering with it tonight.

 

[cruiser54]

Check that CPS output, too. Could be weak or on the brink of failure.

 

[Ecomike]

Hey guys I got a '89 Renix 4.0 that's having a long crank time issue. I initially thought it would be the fuel pump so I picked up a complete pump and sending unit, fuel filter, and a fuel pressure regulator. None of this has been installed yet, but I have started noticing that my long crank time issue is only when hot. In the mornings or after sitting a long time, it starts right up.... But if I go into a store and come back out an hour later I get a really long crank time. It sputters a bit at first but no back fire. Any thoughts before I start wrenching on this thing?

Check the vacuum line on the FPR for a gasoline leak while running. It will flood the engine on shutdown. Next time it is hard to start, floor the gas peddle and crank, if it starts that way (give it several tries), then it was flooded, so that means a leaking injector or fuel pressure regulator vacuum port.

Follow the crusier54 CPS plan, but also try a hot air dryer on the CPS before starting it to see if it is affected by heat. I doubt your problem is the CPS due to the temperature issue, but it is possible!

I had the opposite problem once and it was one of the engine temperature sensors that was bad. It also gave me a high idle problem sometimes. Mine was the MAT manifold temp sensor. The other is the CTS.

 

[Ecomike]

It's an automatic, a full tune up was done less than 10k miles ago. I'll check the CPS this weekend. I still might have an issue with fuel dilivery though, I put a fuel pressure gauge on it and the second I shut off the engine I lose all pressure really fast. Looks like the check valve in the pump isn't working.

OK, just read this, so it sounds like a bad FPR leaking fuel in the vacuum line or one or more leaking fuel injectors, 99% sure!!!!! It is one of those!!!!

Try the fuel throttle start test as it shuts off fuel the the injectors to dry out a flooded engine!!!!

Sitting overnight may be drying it!!!!

 

[Renegade XJ]

Ok, as suspected it was the Fuel Pressure Regulator! Starts right up no issues now, also help smooth out the idle A LOT too. Doesn't seem to be running as rich either. The Vac line was full of gas. One other thing i notice is that with the old FPR the gas pressure guage was bounceing between 31-33psi, now with the new one on its solid at 31... Also i have no leak down on the pressure guage either! Thanks for the input guys, I hope this thread will help out some one in the future.