4x4Wire TrailTalk

4.0 long crank

Posted By: fresnodb

4.0 long crank - 10/13/14 06:44 PM

Just wanted to get some ideas. Maybe this was in a previous post but I've been away for quite some time. Picked up an '87 XJ 4.0. Runs great but cranks for an extended time both hot and stone cold. First test was the fuel pressure, it was exactly as All Data said with no significant leak down. Replaced plugs and wires. Any ideas. Thanks, db <img src="/forums/images/graemlins/confused.gif" alt="" />
Posted By: 4x4Wire

Re: 4.0 long crank - 10/13/14 10:56 PM

You may have pressure, but to you have flow rate???

Some notorious issues with the 4.0l....

Fuel filter - The in-line filter needs to be changed on a regular basis.

Injectors - They also need periodic cleaning.

There is also a "throttle position sensor" that drove me nuts with my 89 Cherokee w/4.0l

It has been my experience the fuel pump can give good reading at idle and yet begin failing with the engine under load.

Last resort is the engine control module. But, with that dead, you will have no spark.
Posted By: fresnodb

Re: 4.0 long crank - 10/13/14 11:54 PM

Thanks John. Fuel filter is next, obviously should have been one of the first things. Good time to change fuel lines at the tank.
Posted By: BigJim

Re: 4.0 long crank - 10/14/14 08:20 PM

I'd be swapping the tps first. I'm betting on retarded timing being the culprit. Doubtful it is fuel as you haven't complained about high speed and that is usually the first sign of a filter.
Big JIm
Posted By: fresnodb

Re: 4.0 long crank - 10/17/14 09:33 PM

Jim, that makes sense that I don't have a fuel flow problem thinking back to the old carb and plastic inline fuel filters. As for the TPS, it doesn't matter if the throttle is open or closed when attempting to start. Could it be sending a 'open throttle' signal to the computer when cranking?
Posted By: BigJim

Re: 4.0 long crank - 10/18/14 12:48 AM

Yes it matters a lot. Rarely can a fuel injected engine be started from an open throttle. It's a cheap fix try it.
Or look closely to see if the tps has moved or become loose.
Used to be the coil could cause similar hard starting problems, but it would also cause high rpm problems.
I'm still betting on the tps.
Big JIm
Posted By: 4x4Wire

Re: 4.0 long crank - 10/18/14 06:02 AM

Personally, I tend to be on the anal retentive side with fuel injectors especially when the vehicle has sat for several months.

Filter and injector cleaning should net periodic maintenance. Fuel pump issue tend to reveal problems under load and high speed.

Like Big Jim (and I said), the TPS is notorious for starting issues. You should be able to start a fuel injected engine without stepping on the accelerator.

The TPS is the control/fail point then, provided you are receiving fuel.

In the six years I had my 89 Cherokee, I replaced the fuel pump once and the TPS twice. In the 12 years I have had my 94 Wrangler, I have replaced the Engine Control Module (about $600) and the fuel pump, each once.

Replace the TPS. And, as a general maintenance, replace the fuel filter and do some injector cleaning. I dump a bottle of the injector cleaner in my tank about once a year when I know I will be burning through the majority of that tank.

It does not clean the TPS. As a "trail fix" you might be able to clean the TPS as it can build up a layer of oil and crud. However, changing it and keeping a spare is cheap fix.
Posted By: fresnodb

Re: 4.0 long crank - 08/14/15 07:17 PM

Dumped this one and got a stock '94 YJ 2.5 just like my original many years ago! <img src="/forums/images/graemlins/patriot.gif" alt="" />
Posted By: 4x4Wire

Re: 4.0 long crank - 08/15/15 04:58 PM

The 2.5l is a solid engine. It is a little under power for sand dunes but has reasonable low end torque for most situations.
Posted By: Jim_Paget

Re: 4.0 long crank - 08/24/15 03:10 PM

Had a vehicle in the past where the long crank issue was caused by leak down in the fuel system, i.e., there was leak that caused the injector system not to hold pressure particularly overnight. Once the engine starts can you shut it down and then restart it immediately? If so, then look for a pressure leak somewhere in the system. It probably isn't something that you can find visually. You may need to put a pressure gauge in the line and then check the pressure in various situations. It may be an injector seal.
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