Long crank start

[Phoenix of Fury]

I know, I have searched, and many say the CPS for the 4.0L. I've got an '86 with the 2.5, and it has an excessively long crank to start... So long, that it killed my battery before the truck actually started.

 

I know when the truck is about to start, because the RPM meter will just stay low when it's cranking... And once it starts flailing about wildly, the truck usually starts. But the RPM meter didn't move at all...The truck just cranked, and cranked, and cranked...

 

Is this a symptom of a CPS on this system, or something more? This has only started happening recently.

[smartazz19]

My long start was related to Fuel. I replaced the fuel filter and it started a little faster. Wires/Plgs good? Not fouled or anything?

[dragonrider477]

the rpm meter(tach) needs a primary ignition source to "wiggle the needle" while cranking the engine. back when honda cars had a lot of ignition module failures,i used the "watch the tach while cranking" method to determine this.if the tach did'nt wiggle,i replaced the module(primary ign.).if the tach wiggled when i cranked and i had no spark,i replaced the coil-cap-rotor(secondary ign.)the manche needs a cps signal to wake up the primary ign.look at that first.the module will just lay there dead without it.check all wiring connections and grounds.jeep wiring was'nt great when new and is'nt any better after 20+ years.

[Phoenix of Fury]

Thanks, I'll check the fuel filter and wires and plugs. Its only got 80k on it, but since it's 22 years old, I should probably replace the wires and plugs I guess.

 

I should have stated in my first post - The truck only behaves this way when it's been sitting for more than say, 12 hours. Once its been started and driven, it usually starts without problems for the next couple of hours.

[brigarpeon]

I had 2 problems with my 2.5 CPS; Long Cranking time and a No Start. The long crank was fixed by removing and cleaning the CPS. Grease,dirt oil had turned into sludge that was so thick I had to clean the bolts to find them. Sludge was also coating the sensor side of the CPS so I spun the flywheel little by little til it was clean too. The no start was due to an issue in the wire connection plug from the CPS to the main harness. My 2.5 usually turns over 6- 10 times before it fires up but from what I read this is normal by design.

[brigarpeon]

I had 2 problems with my 2.5 CPS; Long Cranking time and a No Start. The long crank was fixed by removing and cleaning the CPS. Grease,dirt oil had turned into sludge that was so thick I had to clean the bolts to find them. Sludge was also coating the sensor side of the CPS so I spun the flywheel little by little til it was clean too. The no start was due to an issue in the wire connection plug from the CPS to the main harness. My 2.5 usually turns over 6- 10 times before it fires up but from what I read this is normal by design.

But as others have said the fuel filter will make it crank to start and the pressure must be 14 - 15 psi at the TBI port. A new fuel filter won't hurt and it's ez enuff 2 do. If pressure is still low at the TBI port you can adjust it higher at the regulator. If you can't the fuel pump may be going.

[Phoenix of Fury]

Took off the CPS yesterday (Not too bad on a 2.5L), and took it to a few stores. Of course, no one had one in stock...

 

I replaced the fuel filter and put the old CPS back. Seems like she wants to fire now, but my battery is too drained.

 

I ordered a new CPS as a precaution...The guy calls me today and tells me there is only one left in the county, in VA?

 

I'll post an update when I either fire it up, or replace the CPS.

[Randy in Maine]

Ever test the residual fuel pressure?

[zukidave]

At the jeep shop I work at we see this all the time on the XJ's.

The problem is the rubber elbow in the tank.

The rubber get's hard with age and does not hold residual pressure

so the pump has to build line pressure in the fuel line.

 

Cycle the key a few time's and if it start's better then that's your problem.

You can see what I'am talking about if you use a fuel pressure gauge

and watch the gauge as you cycle the key

[Phoenix of Fury]

Well I finally got a jump today, and it started with no problems...Only cranked like twice before it fired up.

 

I will probably replace the CPS as a precaution, and remove the connector, splicing the wires directly together. At least that way, I'll have a good trail spare.

 

I noticed one other weird thing about the fuel pump. I drove it a short distance to get gas, and when I removed the gas cap, the tank was pressurized. I'm guessing this is normal. But is it normal for the tank to actually *pop*? It also seems to do it anytime I turn the engine off, the tank will *pop* back out after 3-5 minutes.

[Eagle]

I would strongly recommend that you do NOT remove the connector and splice the wires. You'll just be making things more difficult for the next time you replace the CPS. It is intended to be replaceable -- it's a "consumable" part, although the interval is *normally* between 100,000 and 150,000 miles.

 

The problem is that in the models before mid-1990 the main wiring harness that the CPS connects to is too long and too small, so there's a voltage drop between the CPS and the ECU. When the CPS gets old and doesn't generate a strong impulse, the ECU doesn't read it. There is a wiring harness patch to run a pair of wires directly from the CPS weatherpack connector directly to the ECU. I would suggest you get that, install it, and keep the plug-in connector on the CPS.