lurk520

Hello,
Don't really know where to begin here. Well I bought a 93 XJ 4.0 Auto trans a couple years ago. It has always started on the first crank, but on a cold start it starts funny, either fires up really quick (instantaneously), or too slow, or sounds weak, and sometimes sounds just fine, but never seems to be consistent except that it starts on the first crank every time. I put it in a shop before and they couldn't find any obvious reasons, they claimed it was the fuel injectors and cleaned them, but it didn't fix the problem and I really don't believe this is the root cause. I never got into throwing parts at it since it always starts anyway. Now here's the kicker....I just bought an 02 Grand Cherokee with the 4.0 and it has a really similar way of starting, almost seems to be exactly the same thing ....Is this just the way these 4.0's are? I don't really want to dump a bunch of money into parts and get no where... I've posted this problem several times before but really haven't got much info.

lurk520

additional info: Starts fine when warm, I have changed spark plugs, battery, CTS, CKP, I have checked fuel pump pressures and MAT sensor and both checked out fine as well. (On the 93 XJ)

tjwalker

No, it's not inherent to the 4.0 These engines should start cleanly and quickly. The 87-90 take a little bit longer cranking time due to the design.

1. For your 2002 Grand Cherokee, it's not at all uncommon to have a check valve problem. Read my information on this issue below.

2. For your 93, a clean start rides on many things. If it "sounds weak", be sure starter is up to snuff and the battery and charging system behind it. Be sure all tuneup parts are fresh including plugs, wires, cap, rotor, fuel filter. Secondary ignition is critical for quick starts. Also freshen your engine grounds. More on that below. You also could have a bit of a checkvalve leak as well that is reducing your fuel pressure, so some of the information below applies to your 93 too, except your fuel delivery setup is different than the newer ones as your fuel pressure regulator is under the hood and your 93 operates on 31 psi, not 49.

For BOTH of your vehicles, try the poor mans prime that I outline below. If this helps, it is telling you that you are losing fuel pressure as the vehicle sits.
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The check valves (there are two of them; one on the fuel pressure regulator and another on the fuel pump) are part of the fuel pump assembly on 95.5-2001 vintage 4.0 XJs. When a check valve starts to fail, it can reduce fuel pressure to a point where an extended cranking time is needed to start the engine. It is a very common failure. I experienced it on my 99 at around 75K.

A good (and simple) first step in helping you troubleshoot this problem is called “the poor mans prime”

1. Turn key to ON position (do not crank the engine!)
2. The fuel pump will energize and run for a couple of seconds
3. Turn key to OFF position
4. Repeat above steps 1-3 two more times
5. NOW crank the engine over

If the engine starts quickly and cleanly after performing this procedure, you may have a check valve issue. If it starts and runs poorly for a few seconds, it could also be a leaky fuel injector resulting in the fuel pressure leaking down and the subsequent stumble upon startup is the engine clearing the excess fuel that has leaked into the cylinder because of the faulty injector.

Also be aware that a bad battery can give you starting symptoms as well. Have your battery load tested (any parts store will do this for free) if you have any doubt; your XJ does NOT like low available battery voltage. Be sure battery connections and posts are CLEAN.

Some troubleshooting tips for extended crank times. You will need a fuel pressure gauge. Many parts stores will rent you this tool inexpensively.

*Hook up fuel pressure gauge on the schrader valve on the fuel rail under the hood

*Start engine and bring to normal operating temperature.

*Observe fuel pressure gauge. Normal operating pressure should be 49.2 psi (plus or minus 5 psi)

*Shut engine off.

*Observe pressure on gauge. Pressure should not fall below 30 psi for five minutes.

If pressure falls below 30 psi, it must be determined if a fuel injector, a check valve within the
fuel pump assembly, or a fuel tube/line is leaking. An adaptor tool/hose included with the fuel pressure gauge can help you with this. Consult the manual that comes with the fuel pressure gauge and the Factory Service Manual for your year XJ for more information on this exact procedure, but here is basically how it works:

*Turn the engine off and immediately clamp the fuel line at the adaptor hose. Watch the pressure gauge and see how long it takes to lose pressure.

*If the pressure remains at 49 psi for an extended period of time then the problem is in the tank – most likely a check valve. If the pressure falls below 49 psi fairly rapidly then the problem is probably a leaky fuel injector.

**Note. Where check valve is suspect, a quick loss of fuel pressure is often the fuel pressure regulator check valve and a slow loss of pressure is often the fuel pump check valve. But keep in mind that either or both check valves can be to blame.

You can limp a check valve problem along indefinitely if you like, as it doesn't mean the fuel pump itself is going to fail. Perform the “poor mans prime” before cranking to speed up your starts. However, if you have a check valve issue and want to resolve it, it is recommended that you replace the entire fuel pump assembly for two reasons. First, you have to drop the gas tank to access the assembly. Secondly, with two check valves, replacing just the fuel pressure regulator where one of the check valve resides may or may not resolve your problem; remember there are two check valves; the other one is on the fuel pump.

The fuel pump assembly consists of fuel pump, fuel pressure regulator, fuel gauge sending unit, fuel gauge float, pickup filter and pigtail wiring harness. If you do replace the fuel pump assembly, purchase a high quality unit; you do get what you pay for here. Some cheap aftermarket assemblies have been known to fail prematurely. I personally prefer Bosch fuel pumps as they manufacture the best fuel pump assemblies for the XJ. Carter is my second choice. Airtex is my least favorite choice and I will not recommend or install them.
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Grounds can be the root cause of many electrical gremlins. Refreshing grounds is NEVER a bad idea, and the investment of your time in this procedure is always well worth it!

You can't tell much of anything by looking at ground connections!! You must remove, scrape, clean until shiny the cable/wire ends and whatever they bolt to. Be sure to remove all paint from any ground connections.

Start with the one on the back corner of the head, and where it attaches to the firewall, as it deteriorates over time and is an area that makes it susceptible to damage. Best to replace that woven cable with a #4 or #2 gauge cable. You can attach the one end to the intake manifold if you would like.

Next go over to the engine dipstick tube stud. Remove the nut and clean the wire ends and scrape the block until shiny at the stud. Reattach tightly.

If you are so inclined, add at least a #6 cable from the negative terminal of your battery to one of the bolts on your radiator support.

lurk520

Well I rented the fuel gauge set-up from Auto Zone before and the fuel pump checked out perfectly. As for the starter....it's had oil leaking on it for years, I'm surprised it hasn't died, but would that cause it to act weird on a cold start but be fine once warmed up?

tjwalker

The next time you start either of your Jeeps when COLD, try the poor mans prime that I outlined.

It is a very simple but important test to help you determine root cause. You can have a fuel pump that passes the pressure test, but because of a bad check valve, it leaks down fuel pressure over time as the vehicle sits. I've seen it countless times.

Report your results.

MossyXJ

i love my cold starts... bad IAC sensor.

lurk520

The 93 also has an exhaust that bangs the cross-member but that's a whole nother story, will also be sold in the next couple days. Replacing it with the 02. I thought it was peculiar though how they both have an inconsistent cold start.

lurk520

The WJ seems to be having an intermittent long crank on cold starts. Is it practical to just replace the check valve on a fuel pump if that is the problem? Or does the whole pump need to be replaced?

tjwalker

Did you try the poor mans prime? Did it help?? Really need the results of that test to help you isolate this.

There are two check valves on your WJ. The primary one on the regulator but there is also one on the pump. Because of that and because the gas tank has to come down, it's best to replace the entire fuel pump ASSEMBLY while you're in there, and not piece meal this repair.

lurk520

I'm going to start doing that. Being an intermittent problem it will take a couple days to tell if that helps. I've got a 60 day warranty from the dealership. Hopefully they'll put in a new one for me. Being intermittent it will probably act perfect if I take it in there.

lurk520

I did the poor mans prime, 2 key cycles, and it still long cranked. Like I said though it's intermittent. Haven't had a chance to check the fuel filter either.

lurk520

Actually I don't think the warranty will fix this because it says in the event of a mechanical break down. And being a Jeep it will run like this forever with out breaking down.

lurk520

I did the prime again, this time 3 cycles and it sounded like it was a little flooded, it stumbled on the start up, not too long of a crank either.

TheJerm

What is a long crank? Not instantly or takes 5+ seconds to start while cranking?

You could just be nit-picking on how older motors start. I too have a slow crank in the cold (less than 35 degrees) and cant shift into 2nd till the tranny warms up. Ive just come to expect it with 230K miles

lurk520

It either starts too quick , less than one second, or too long about 4 seconds. Nothing to do with ambient temp. You can tell the difference in a clean start and a funky one. I have never heard a vehicle start as quick as this one, it's almost like it doesn't crank, it just starts right away, it's that fast. Also I've owned a 77 Nova and an 86 Olds, both with old motors that start clean and consistently every time.