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Why's it take so long to start a 4.0?

Z

Zoro

NAXJA Forum User
Location
Colorado
For some reason every 4.0 in a Jeep that I've ever seen seems like it take forever to start, why is this? Is it a bad thing?

-Zoro-
90 XJ
 
Usually from a bad check valve in the fuel line, lets the pressure bleed off so when you try to start it the pump has to puressurize the system first. Good test is to turn the key to 'on' and count to 30 then go to 'start'. If it fires right up it's the check valve/fuel pump assy.
 
From what I've heard, the fuel pump relay will not energize the pump unless you have a minimum amount of oil pressure (which could save your engine if you run low). It takes some turning for the oil pressure to build up on startup, but that oil in the bearings on startup adds many miles to the engine's lifetime!
If your 4.0 is taking a while to start, your bearings are wearing, your pump is wearing, or your battery/starter are not turning the engine over as fast as they could.
This is just what I've heard though, I've got a MPFI 3.4 after the 2bbl carbed 2.8 wore out around 400,000kms. Looking forward to getting a 2000 or so Cherokee!
 
mine took an insane amount of time when i bought it. I changed the fuel pump and filter and it got better but still cranked slow, then i replaced both battery cables to 0 AWG and now that puppy spins fast. it starts real fast if i let the pump prime the system first. its ALMOST like a normal car not quite but almost, i think its just the nature of the beast
 
I bought 5 inline fuel check valves from a marine supply store (online), for an OMC outboard for $10 and change. Haven't put one in yet...will this spring when I replace floor pans. BMW makes a check valve that can be used but I had a hard time locating one.
 
My 87 Pioneer has a new fuel pump. I just turn the key and listen for the fuel pump to stop running and it start's within 2-3 seconds. On rare occasion it doesn't start so I do the same thing again and it fires right up.

Can't say nothing but good stuff about the SeaFoam that everyone here brags about. Wow, that really did the job maybe a bit of that may help you?
 
Maybel, you hear wrong. The fuel pump energizes as soon as you hit the key. What takes a while is that the sensors have to figure out the position of the crankshaft before firing the injectors and spark plugs. This takes something like 1.5 revolutions worst case. It sounds like a lot more, but have someone crank it while you watch the crankshaft dampener. It will surprise you.
 
I have a 2000 xj and mine hesitates a good bit when its cold in the morning. But for some reason when i turn the key to acc for a few seconds it cranks right up!
I am thinking about a red top batt. Maybe it will help.
 
NCXJMAN said:
I have a 2000 xj and mine hesitates a good bit when its cold in the morning. But for some reason when i turn the key to acc for a few seconds it cranks right up!
I am thinking about a red top batt. Maybe it will help.
Click to expand...

That's because when you have the acc on for a few seconds, the fuel pump turns on and pressurizes the system.
 
dizzymac said:
I bought 5 inline fuel check valves from a marine supply store (online), for an OMC outboard for $10 and change. Haven't put one in yet...will this spring when I replace floor pans. BMW makes a check valve that can be used but I had a hard time locating one.
Click to expand...
I would think that a marine check valve would not handle the high pressure of fuel injection.
 
NCXJMAN said:
I have a 2000 xj and mine hesitates a good bit when its cold in the morning. But for some reason when i turn the key to acc for a few seconds it cranks right up!
I am thinking about a red top batt. Maybe it will help.
Click to expand...
Save your money, better starting is not what a red top is for.
 
Mine starts fast everytime- plugs and wires are at least 3 years old, most likely much older, the starter has been soaking in oil from above for at least that long, and the battery is a cheapo wal-mart special (with corroded terminals/connectors.).

I don't know what all this long starting stuff is about-

good luck.

B
 
sjx40250 said:
It depends upon the year. 1990 and older take longer. Letting the fuel pressure build makes a big difference.
Click to expand...


Yes the renix ignition/fuel injection sys on pre 91s requires a slightly longer crank time to fire up. Usually a count of from 2 to 5. Apparantly this is programed into the ecu for reasons not always clear to us. However a side benefit - more oil is pumped during cranking before the start up. Greg
 
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