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Slow starts

There is a several second delay while the fuel pressure comes up. Try turning the switch to on and wait 5 seconds before cranking. You will see the difference in how fast it fires. Actually the slow fire helps let the oil pump build up a little pressure before it fires.
 
Is it a Renix system? If so they tend to take two revlolutions of the engine for the computer to sync on the CPS (crank position sensor). Most all older non ho xj's seem to be that way but. I don't know how they started when they were younger.

JoBo
 
My 90 is the same way. I've replaced the cap, rotor, wires, battery cables, fuel filter and it's still just as slow. Especially during these winter months they just don't start too quick.
 
My '90 is the same way. I did have it wired that the NSS was bypassed and started a bit faster, than it does now that I've cleaned it and disconnected the direct connection to the starter relay. I know of an '89 that does basically the same thing as well.
 
Replace your battery cables. The renix computer requires several revolutions before it will start. New battery cables will make the starter turn faster, and thus, make the engine start faster.
 
the engine has to reach about 300rpm's before the ECU "wakes up"

this is to promote better oil circulation throught the engine before it fires, yeah mine takes a while to crank and that's with a yellow top

oh well...........
 
my 99 skipped a couple beats while cranking tonight on my way home. It sounded fine, and it wasn't a slow slounding crank, just like it missed a couple turns. I know my battery connections are in need of cleaning, and i'll probably replace my battery once my 30 warranty is up, anything else I should I be concerned about? Or am I just being paranoid?

BTW, what's the MAIN difference in a High Output 4.0 and a Non High Output 4.0, other than the obvious? I thought ALL the 4.0's were H.O.
 
Last edited:
99XJSPORT06 said:
BTW, what's the MAIN difference in a High Output 4.0 and a Non High Output 4.0, other than the obvious? I thought ALL the 4.0's were H.O.
Click to expand...

HOs have a different intake/exhaust manifold, throttle body, computer, head, and possibly the cam.
 
ah, ok. Didn't know there was a difference. Were all of them H.O. after a certain year? Or was it still an extra?
 
After you've checked and done everything else replace the starter. My was acting the same way. I eventually had to start jumping the starter until it just up and died. Now it starts nice and quick.
 
Oddly enough, I had longer starts until I unplugged (both) my O2 sensors. Not sure why. I know yours has only one O2 sensor, but I don't know if it makes a difference. Anyway, it's easy to just unplug it (then disconnect the battery to reset the computer), then see if it starts faster.
 
On my 88 XJ I solved the problem my installing a new fuel pump. The check valve internal to the fuel pump after some period of time fails to hold pressure. You should get a fuel pressure gauge and check the pressure once you turn off the engine, the manual tells you after 30 or 60 minutes the fuel pressure should bleed down so may psi. If you pressure bleeds down then the check valve is suspect.

The test procedure also tells you how to check to make sure it the check valve or the fuel pressure regulator. Either one can be the cause. There been posts of installing a BMW fuel line check valve to avoid replacement of the fuel pump, do a search.

Time to buy or barrow a fuel pressure gauge and figure out what going on.
 
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