'92 YJ 4.0 slow starting - fuel issue

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AwesomeJ10
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'92 YJ 4.0 slow starting - fuel issue

Post by AwesomeJ10 »

I'm wondering if anyone on here has any insight to the early fuel injection on the YJ's?

My wifes '92 YJ with the stock 4.0 and stock fuel injection is SLOW to start, but runs fine once started. The reason it's slow to start is because it's not getting fuel pressure to the fuel rail until it cranks over for several seconds. Once fuel pressure develops, it starts right up.

How do I troubleshoot why it's taking so long to develop fuel pressure? The fuel pump comes on for a second when we turn on the ignition...
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Stuka
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Re: '92 YJ 4.0 slow starting - fuel issue

Post by Stuka »

'92 will have an HO, and not the older renix system. The renix systems actually had to hit a certain rpm (350 as I recall) before they would even try to fire.

What happens if you hold the key in the run (not start) position for 10 seconds or so before hitting start? You may need a fuel pressure gauge to troubleshoot this.

My first thought is either a weak pump, plugged filter, or plugged fuel sock in the tank.
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Re: '92 YJ 4.0 slow starting - fuel issue

Post by AwesomeJ10 »

Hey Stuka - I've re-wired the entire key switch/ignition because the key messed up while my wife was on the hwy. The problem that I'm talking about started before the key issue.

I have a master ignition switch that turns on everything and I can hear the fuel pump come on, but no fuel comes out when I tested the fuel pressure on the rail.

I've replaced the fuel filter, but the pump and the sock are stock.

I'm preparing this thing for Moab EJS and want to 100% fix it before hand and have plenty of spare parts to lug around.

How does the CPS come into play here? I'm thinking about replacing the entire tank, skid, pump, sock, CPS and maybe a few other things...
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Stuka
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Re: '92 YJ 4.0 slow starting - fuel issue

Post by Stuka »

Have you put a fuel pressure gauge on the rail while starting and after its running? It would also be worth doing a leak down test. I cannot recall the specs for the 4.0 pump, sure google can get them for you. But if you run a test to see how fast it gets to pressure, and how long it holds pressure, it will probably show the pump is weak. Slow starting is typically a sign of a failing pump or plugged sock.

Since it is most likely the OEM pump, its where I would look.

I know the CPS comes into play when starting a Renix 4.0. There will be no spark until the engine hits X RPM. But I did not think the HO was that way.
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AwesomeJ10
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Re: '92 YJ 4.0 slow starting - fuel issue

Post by AwesomeJ10 »

cool

well my wife is getting a new pump and sock and we will look into replacing that tonight. I think we need to cut an access hole to make future pump replacements easier...

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Re: '92 YJ 4.0 slow starting - fuel issue

Post by AMC_Don »

I had a 91 xj that did that. I replaced the fuel pump & sock & never had another issue with it.

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Re: '92 YJ 4.0 slow starting - fuel issue

Post by fedexmonster2004 »

I replaced the fuel pump and filters and injectors started great for about two months then it started doing the slow starts again mine was a 97 g c


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letank
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Re: '92 YJ 4.0 slow starting - fuel issue

Post by letank »

The CPS is sensitive to oil... if it gets too oily... it starts to act up (used to own a YJ with the 2.5l)
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Re: '92 YJ 4.0 slow starting - fuel issue

Post by AwesomeJ10 »

I ended up losing this jeep as she is now my Ex.

But - the problem with the slow starts on this jeep was a bad fuel hose in the tank. The host that connects the pickup to the pump was cracked, so it wasn't sucking fuel correctly.
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