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Very Odd Hard Start

X

XJHummerRescue

NAXJA Forum User
Location
Denver, CO
'89 Jeep Cherokee Sport, 2 dr, 4.0, AW4

Starting very recently, say 3 or 4 days ago, I have been having an odd hard start problem, and it is very intermittent. Once in a while, no matter the temp. of the engine or the outside temp. I will have to crank it for 10 seconds or so, then stop, try again, then stop, then usually on the third cranking session it will start... But other times it starts up in 2 seconds or less. And either way, when it starts, the engine runs great! No problems with high or low idle, nor hesitation or stumble. Checked all vacuum lines (except for my disconnected EGR vacuum line, but thats a different story), and electrical connectors. I dont know where else to look. Does anyone have any input?

Thanks
 
Have you checked the fuel pressure? Try turning the key ON for a couple seconds before you turn it to START. If you have a gage, use it.

RENIX are known for taking a couple cranks to start - that's in the ECU. It waits until it reads 300rpm AND gets a valid SYNC pulse from the cam/distributor sensor. If that's good, it starts. If it doesn't get a SYNC pulse, it can start "guessing" when the #1 comes up - that should be fairly obvious when it happens. I've not heard of any SYNC sensors blowing anywhere - yet.

There's a thread here on the fuel pressure subject - try searching "fuel check valve," or something like that, for ideas.

5-90
 
It turns over pretty fast, that doesnt seem to be a problem. I will try checking the fuel pressure. It's getting worse too, as I just tried to start it up to leave, and after 5 cranking sessions, it still wouldnt start...
 
Okay, answered my own question, and it is no... But i depressed the button(not sure what to call it) and fuel didnt spray out... more like spilled out... Like I have nearly no fuel pressure. I can hear the fuel pump prime though. I may just go ahead and replace the fuel filter, but how do I check the fuel pump and pressure regulator?

Thanks
 
XJHummerRescue said:
Okay, answered my own question, and it is no... But i depressed the button(not sure what to call it) and fuel didnt spray out... more like spilled out... Like I have nearly no fuel pressure. I can hear the fuel pump prime though. I may just go ahead and replace the fuel filter, but how do I check the fuel pump and pressure regulator?

Thanks
Click to expand...
With a real gauge to start with.
 
Okay, just got a gauge, and I apologize for the time taken to do so, I had a couple of more urgent repairs to do.

Tested fuel pressure (it decided to not start again, so this is key on, engine off) Fuel Pressure Immediately jumped to 33-35 when I turned the key on and heard the fuel pump prime, but even by the time I got the gauge in hand, it had already started rapidly dropping, and in, say 20-30 seconds was down below 20 psi. That really doesnt sound right to me.

Any further testing for me to do? I just checked all fuel lines, and I have no leaks.

P.S.: I did the test 4 times just to be sure it wasn't a fluke, even though I doubted it could be.
 
XJHummerRescue said:
Okay, just got a gauge, and I apologize for the time taken to do so, I had a couple of more urgent repairs to do.

Tested fuel pressure (it decided to not start again, so this is key on, engine off) Fuel Pressure Immediately jumped to 33-35 when I turned the key on and heard the fuel pump prime, but even by the time I got the gauge in hand, it had already started rapidly dropping, and in, say 20-30 seconds was down below 20 psi. That really doesnt sound right to me.

Any further testing for me to do? I just checked all fuel lines, and I have no leaks.

P.S.: I did the test 4 times just to be sure it wasn't a fluke, even though I doubted it could be.
Click to expand...
Thats not to bad, the pressure will come back up when you crank.
Can you hear the IAC motor running after you turn the key off for 3 seconds?
 
Okay, went out and had someone else turn the key on and off, listening for the IAC motor to make a sound, heard a sound when it went to on, but not to off, then had him crank it a little then immediately turn to off. Still didnt hear any sound after he turned the key to off, but it did make a few really funky sounds while cranking, as well as a little cough from the TB... first time i've heard that.

I'm thinking that it needs a good cleaning, and possibly replaced? I doubt it, but due to the sensitive nature of most sensors and connectors i'll ask anyway, will carb cleaner hurt the IAC motor in any way?
 
I cleaned the IAC, and it was barely dirty at all. I thought maybe the IAC motor was seized in its bore, and tried to move it by hand, but I guess this is impossible, it would not move at all. I am going to take off the airtube and watch it move at idle (or cranking, if it wont start) to see if it is working properly. If it does, what should I check next? I am on lunch right now and only have about an hour of daylight to work on it after work, so any suggestions now would be a great help. Thanks :)
 
Check the gap on your crankshaft position sensor.....If you have access to ALLDATA, go to the technical service bulletin on long crank/hard start. This will tell you what gap your crankshaft position sensor should be at. If the small fiber gasket between the sensor and the mount surface has fallen apart, then this will cause a long crank time. This seems to be a more common issue than the fuel pressure.....Just thought that this may help you.
 
I will check, but the CPS was replaced about a year and a half ago when I had a lot of no start problems. No problems until now. I will try and look up there and check the gap. I do not have access to my Jeep on AllData.com, was thinking about it, but can't really afford to at this moment. Maybe I can find the specs somewhere. Maybe one of the bolts worked loose :). Would my TPS being out of adjustment cause any problems like this? I KNOW it's out of adjustment, and just havent gotten around to adjusting it yet. Maybe I'll try that too. Would hate to have to change the crank position sensor AGAIN. Hopefully we'll have this problem pinned down soon, it is my DD and it sucks sitting in the parking lot after work for 10 mins trying to get it to start.
 
CPS being out of adjustment would definetely cause the symptoms you are describing. It may be just loose enough that it has finally vibrated to far out of adjustment. If you have any buddies that work in a shop, or even if you have a regular mechanic that you use, beg a favor or slip them a few bucks to get you a copy of the TSB off AllDATA. If not, bite the bullet and pay someone to correct the issue for you. Just my opinion.
 
mtnxj said:
CPS being out of adjustment would definetely cause the symptoms you are describing. It may be just loose enough that it has finally vibrated to far out of adjustment. If you have any buddies that work in a shop, or even if you have a regular mechanic that you use, beg a favor or slip them a few bucks to get you a copy of the TSB off AllDATA. If not, bite the bullet and pay someone to correct the issue for you. Just my opinion.
Click to expand...
Nuff of this the CPS is not adjustable and there is no spacer just two bolts.
 
Okay, just adjusted TPS, ratio was .783, it is now .829 (close enough). Doesn't sound like TOO much off, but we'll see if the hard/no starts come back. Also, I did check the CPS, and the bolts are nice and tight. There was no fiber spacer or whatever (so langer1 was definately right) and I checked the wires all the way up to the harness and the insulation was intact in all places with no contact to the exhaust manifold, as it went around, up by the pass. back side of the valve cover then across the firewall to the harness above the intake manifold.

Hopefully I wont have to post in this thread again :).
 
langer1 said:
Nuff of this the CPS is not adjustable and there is no spacer just two bolts.
Click to expand...

So I guess thousands of Jeep/Chrysler techs don't know what they are talking about.....Maybe you should read the comment again. At no point did I say that the CPS was adjustable. There is a Technical Service Bulletin that specifies IMPROPER gap of the crankshaft position sensor. This bulletin lists an updated fiber spacer and gap setting for the CPS. The bulletin is available through both AllData and Chrysler. Due to posting limitations I will not put the TSB number or a link here, but I will be happy to pass along that info if you p.m. me.
 
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