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

[Zoro]

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

[mg614]

Mine starts fast

[RichP]

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.

[K2XJ]

cause its usually out of gas ;-)

[Mabel3.4]

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!

[funvtec]

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

[aparke4]

since my optima red top i have had no problems real fast start up

[dizzymac]

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.

[MudslinginXJ]

After replacing the starter and turning the key to run and letting the fuel pump run for until it shuts off, i can start within 2-3 seconds.

[GAllgood]

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?

[old_man]

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.

[NCXJMAN]

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.

[mjma]

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.

That's because when you have the acc on for a few seconds, the fuel pump turns on and pressurizes the system.

[langer1]

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.
I would think that a marine check valve would not handle the high pressure of fuel injection.

[langer1]

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.
Save your money, better starting is not what a red top is for.

[injectedXJ]

How new are the plugs, wires, cap, and rotor? Time for a Tune up Maybe?

[BCParker]

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]

It depends upon the year. 1990 and older take longer. Letting the fuel pressure build makes a big difference.

[Zoro]

How new are the plugs, wires, cap, and rotor? Time for a Tune up Maybe?
New wires, cap, rotor & plugs.

[Greg Smith]

It depends upon the year. 1990 and older take longer. Letting the fuel pressure build makes a big difference.


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

[Pioneer89XJ]

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

True. My 89 took much more time than my 98 does.

[TheBlueSub]

i kno this is an old post but my 1990 takes a good while to start even when i turn the key to acc and let the pump prime...my '85 2.8 took a .5 of a second to start


does anyone else know any other solutions??

[90 Laredo]

I asked my local dealer and they said that some of the 4.0L had a delay built into the computer. This is done to let the oil pump to pump a bit to help eliminate dry start and prolong engine life.

[langer1]

I asked my local dealer and they said that some of the 4.0L had a delay built into the computer. This is done to let the oil pump to pump a bit to help eliminate dry start and prolong engine life.
Your Dealer was blowing smoke up your tail pipe. :laugh3:

[langer1]

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
The real reason is the Renix has no memory so it takes a couple of turns just to reset the timing and fuel mixture.
Thats also is why there's no check engine codes saved.

[grundan]

I know this is an old thread. I've been tinkering with my 87 4.0 and thought it was always gonna be this slow starting heep. Try this next time start yours up.
turn the key on till you hear the pump quit running, (as previously mentioned)
turn your ign. switch over and hold it for about 5 seconds in between the ON position and the start position. that little bit of dead space right between the two and then turn it over and see what happens.
When I do this to mine it fires up in about 1 second. I have no clue why it works but it does. If I go straight from on to start it will start in about 4 seconds or so.

[2001XJeep]

Interesting, I've owned four 4.0's over the years (currently have 3) and have never had the delayed-start problems I hear of so often. I routinely let the fuel pump build up pressure before cranking, which gives an instant light off. But even fully turning the key immediately still gives a 1 second crank time.

Now, our 2002 Mazda Millenia. It would take 3 or 4 seconds to fire, even when letting the pump build up pressure. Never did figure that one out. And that's partly why a 98 ZJ has replaced it :)

[5-90]

The real reason is the Renix has no memory so it takes a couple of turns just to reset the timing and fuel mixture.
Thats also is why there's no check engine codes saved.

Half marks. Not only does the RENIX system not "store" or "throw" codes (it's pre-OBD,) but there's also the fact that the ECU has to receive a valid crankshaft position sensor signal (always,) and it wants a valid SYNC sensor signal (which it can work without,) before it will send triggers to the ignition and fuel injection.

I'm wanting to recall that it wants to read 300RPM at the crank sensor as well, but that may be apocrypha - I'm not sure where I picked that up.

The system can work without a valid SYNC signal - it will "guess" until it hits #1TDC compression/fire, and go forward from there. However, it will take a noticeably much longer time starting (don't believe me - disconnect the 3-wire terminal coming from the distributor and try it!) and you will know something is wrong.

I've noted that keeping the battery charged up and staying on top of the starter helps somewhat. I've also got reports from the field that replacing battery cables (which are probably old anyhow, and not as well-sealed or as large as they really should be) also helps - this from people who have bought the cables I make. I don't think of that as apocrypha - I've noticed a slight decrease in start/crank times and somewhat faster cranking when I changed my own cables a few years ago - and I haven't lost either advantage yet (but I'm cranky, and tend to overbuild things.) Replacing/upgrading the cables will allow the start motor to draw full requested current, and that allows it to generate more torque, and therefore crank the engine faster (and get up to speed faster.)

I'm still inclined to try the check valve - I've just got to find one I can work with. Max FI pressure for the 4.0 is 39psi, so it's not that high (but higher than the 4-7psi used in carburettor systems, so it's still something to think about.) I haven't tried it yet - but I will give a report from the field when I finally do. Just don't hold your breath - most people do not look well with hypoxia...

5-90

[wilcharl]

Hypoxia can make you so happy though... I like to think of the renix start delay as a good thing.. Someone brought up the fact that it allows oil to start circulating before the heat gets turned on... I will buy that sounds good to me

[BillyBob]

One other thing to consider is that when you turn the key to the "start" position, not only does the fuel pump need to get a head of steam to push the fuel up to the fuel rail, but the starter is drawing quite a bit of current to get the engine to spin over, so the fuel pump will have a harder time at this point as opposed to when the engine is running. I haven't looked at the wiring schematic, but if the fuel pump resisitor was removed from the circuit during the "start" mode this could improve starting the engine slightly as it would see a little more voltage.

[5-90]

The fuel pump resistor was added for the 1988 model year, and was offered as a "voluntary recall" for 1987 due to fuel pump noise (I don't see why - a little noise is a good thing. Where are our priorities?)

You can baypass the ballast safely - my 1987 doesn't even have one, and I pulled out the resistor in my second 1989. It makes the fuel pump just a little louder (there's a discernable "hum" when you bypass the resistor,) but it doesn't cause any trouble, and eliminated a potential point of failure.

It's mainly there because people have some silly idea that a Jeep should make about the same amount of noise as a Lexus (I don't know where that idea came from... It's a truck, more than that, it's a Jeep! Dammit, it's supposed to be noisy!)

5-90

[Ron Hyslop]

The Renix xj's require two pulses from the CPS before ignition.

[grundan]

FWIW I did replace all my cables as well as the starter cable with welding cable w/copper ends soldered on. new battery as well.

[scca28]

The fuel pump resistor was added for the 1988 model year, and was offered as a "voluntary recall" for 1987 due to fuel pump noise (I don't see why - a little noise is a good thing. Where are our priorities?)

You can baypass the ballast safely - my 1987 doesn't even have one, and I pulled out the resistor in my second 1989. It makes the fuel pump just a little louder (there's a discernable "hum" when you bypass the resistor,) but it doesn't cause any trouble, and eliminated a potential point of failure.

5-90

I had thought about bypassing my ballast also. However, looking at the schematic in Haynes, it looks like the output from the ballast also goes to the ignition module. Many years ago, I had a '76 Audi Fox who's PO had bypassed the ballast to the coil, and it took me 3 coils before I figured out why they were burning out. Also, if you look at the schematic, it looks like the ballast is temporarally bypassed when the starter relay is in the start position. So, our fuel pumps are getting a full jolt at "start" anyway before the ballast takes over in "run". I haven't had a chance to check yet, but does anyone know what the difference in voltage is at the pump with and without the ballast?
'88 Laredo 4.0 Auto

[5-90]

Make sure your starter mounting pad is also clean - I've been kicking around experimenting with a "starter ground" cable, probably mounted to one of the mounting bolts. Haven't evaluated the utility of such a thing yet - but if you're got a dirty mounting pad (or an oil leak above or forward of the starter,) you'll contaminate the ground path for the start motor and that will also create cranking trouble (don't ask how I know, but it's fixed now!)

FWIW, I've long since installed a rocker to handle the START circuit from the keyswitch (partly for additional confusion, and partly because I had the parts handy when the ignition switch was going out...) I therefore turn the key ON, and then have to hit the rocker with my other hand. The second or so between the two seems to be enough time to let the fuel pressure build up, and it will kick right over in about two turns.

Granted, they're two fairly slow turns (compared to engines with shorter crankshafts...) but that's probably got more to do with inertia at the forward cylinders than anything else. The longer you make an engine, the longer it takes to get up to cranking speed - I had to work on a straight-eight years ago that took about half again as long to start as my RENIX...

5-90

[87manche]

you're correct on those points, but the ballast resistor was solely a NVH thing. My 87 doesn't have one and it does hum, and it's got the OEM coil after 250K miles.
The fuel pump does get 12V when in the start position.
The ballast resistor drops it to about 9V if I remember, but that may be wrong.