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View Full Version : long crank time?


saweddoffjeep
October 5th, 2006, 09:46
so my xj has a long crank time whenever i try and start it up, it takes about 3 seconds or so till it starts. now i know my starter is good its brand new and my CPS is needing replacement, would the CPS be the cause of this or is it something else?

jeepdude10000
October 5th, 2006, 10:04
ok first of all we need more info on ur jeep, year, motor, ect.

but it sounds like its about 88 - 90 year, if it is then the staring time is normal.

saweddoffjeep
October 5th, 2006, 10:06
89 cherokee inline 6 cyl

so that is normal starting time?
one of my friends has an 88 and his starts right up

jeepdude10000
October 5th, 2006, 10:13
u will find that most jeeps of those years will take longer to start, its just the Renix fuel injection. Some say its waiting for some sensor, to read.

theres quite a few threads on this but i could not find on e off hand, i will still look.

saweddoffjeep
October 5th, 2006, 10:16
alrite thanks alot

jeepdude10000
October 5th, 2006, 10:16
here is a lot of info on this


RENIX wants valid signals from BOTH the CPS (Cranskhaft Position Sensor) and SYNC (camshaft position sensor) before it will fire the fuel injectors and the ignition - and it wants to see an estimated crankshaft speed of 300rpm. There are various reasons posited as to why - many apocryphal - but we learn to live with it.
RENIX will start without a valid SYNC signal (it will "guess" until it hits a runner, I've tried this,) but the condition is quite obvious. RENIX will NOT start without a valid CPS signal - and if your CPS is on the way out - or has a shonky connection - that could delay starts.
The engine will start right up with Tbody cleaner for much the same reason it will with ether - it's easier to light than gasoline vapour, and probably ignites upon compression. Once that gets started, and the ECU starts firing fuel injectors, it becomes self-sustaining.
Also, failing/corroded/dirty mains can cause slow crank (delaying starts,) and a dirty/corroded/failing ground strap from the cylinder head to the firewall WILL cause trouble (it's called a "RENIX Killer" for a reason!)
Also, a failing/dirty TPS (yours is probably getting old...) will cause trouble with starting. It usually won't prevent starting, but make starting more difficult and cause idling trouble.
Check, in no particular order:
CPS connection (3-pole Delphi Weatherpack with two wires in - you'll see this at the back of the fuel rail. And, a good sensor should show something like 125-275 ohms at ambient temperature.)
TPS action/adjustment (better to check with analogue ohmmeter, than digital. You're looking for a clean, smooth sweep of the needle when you move the throttle)
SYNC sensor (Use analogue voltmeter set to 15VAC. Backprobe with wiring still connected - + lead to BLU wire, - lead to GRY/tracer. Crank engine, you should see about 5VAC.)
Check for vacuum leaks (just for giggles - these can cause all kinds of Hell!) at the manifold mounting surface, throttle body base, and all Nylon engine management vacuum lines. Vacuum lines can be had from NAPA for RENIX - about $50/set, and all three part numbers you'll need are posted on here somewhere...)
Report back after testing, and if you need more detailed test instructions, we can help you.
5-90



The CPS is at 1100 on the rear of the engine, screwed to the bellhousing. You should be able to see it from up top, but it's easier to access from below... (damn. AMC got something wrong there!)
The SYNC sensor is in the distributor - if you pull the cap off, you'll see the rotor. There's a sort of plate under the rotor, and the SYNC sensor is under that. Replacing it requires removing and disassembling the distributor. Access it electrically by the three-wire connector coming out of the distributor.
You already know where the TPS is, since you changed it. Bear in mind that it's set referring to a percentage of the reference voltage supplied by the ECU - so it's not an absolute. Work with the voltage signal as supplied, and divide it according to procedure (which I'm not looking at at the moment...)
You can get a set of "Weatherpack" tools from your local, which would allow you to remove the pins in a Weatherpack and clean them individually - thus doing a better job. I usually use a plan "brass toothbrush" for basic cleaning, or an old toothbrush and cheap toothpaste (NOT gel!) for deeper cleaning - remove the part and rinse with the hottest water you can stand, then reassemble...
5-90

More like two or three - but the engine cranks faster than you might think, when the starter, battery, and mains cables are all in good condition.
Also, try turning the key to ON and leaving it there for a couple seconds (don't turn it off!) and crank it.
Throttle body cleaner/carburettor cleaner is flammable. Not quite so much as ether (starting fluid,) but it will still burn and provide a fuel when cranking.
Apparently, as fuel pumps get older, they may take a little longer to develop spec head pressures - there may also be a check valve in there to maintain pressure for a little while, and that might be getting old as well. To support that argument, I do note that my 88 starts quicker during the day (while running errands,) than after sitting overnight...
5-90

jeepdude10000
October 5th, 2006, 10:19
BTW nice to see more Cadadian on this site.
Welcome.