Timmaay Posted June 4, 2008 Share Posted June 4, 2008 New here and have a question about my new (to me) Comanche. When I go to start it, it takes 3-4 seconds to start. I've tried putting it to the run position a couple times to build up fuel pressure and it doesn't make a difference. It runs and drives perfect otherwise. I'll do a full intro to my jeep when I get some pics. Link to comment Share on other sites More sharing options...
Pete M Posted June 4, 2008 Share Posted June 4, 2008 A long start period is common for older Jeeps. The problem is usually an aging CPS (crankshaft position sensor). The CPS is situated above the flywheel and has a little magnet inside that jumps when certain teeth in the flywheel spin by. This tells the computer exactly where the engine is in its rotation. As the CPS ages (or the wires associated with it corrode), the signal gets weaker and it takes a few more rotation for the computer to be sure what's going on. Perfectly normal, but eventually the thing might stop altogether. Could be years from now. Could be next week. My 88 has been like that since I bought it 10 years ago. Link to comment Share on other sites More sharing options...
Timmaay Posted June 4, 2008 Author Share Posted June 4, 2008 thanks for the quick reply, now I just need to shop around for a cps. Link to comment Share on other sites More sharing options...
james750 Posted June 4, 2008 Share Posted June 4, 2008 Pete, u said corroding wires, does that mean that the wiring needs to be replaced along with it? I though 5 secs was a fast start time (thats about how long mine takes). my dads xj (admittedly we know that the cps is going out) takes a good ten seconds cold crank time to start. my moms xj on the other hand maby takes 3 cranks. e Link to comment Share on other sites More sharing options...
Pete M Posted June 4, 2008 Share Posted June 4, 2008 It's possible. Some guys have luck with simply unplugging the connector and cleaning up the contacts. Eagle knows it better, but there was an official "fix" for the weak CPS signal involving hard wiring the CPS directly to the computer, rather than letting it wind its way through the factory wire harness. Link to comment Share on other sites More sharing options...
BLHTAZ Posted June 4, 2008 Share Posted June 4, 2008 The long start is a trait of the Renix system engines. Mine does it too and when I thought it was a problem and tried to fix it, I found that there is no fix for it. The only thing that seemed to make a little difference is when I put the new injectors in it. Link to comment Share on other sites More sharing options...
chicofuentes0224 Posted June 4, 2008 Share Posted June 4, 2008 The long start is a trait of the Renix system engines. Mine does it too and when I thought it was a problem and tried to fix it, I found that there is no fix for it. The only thing that seemed to make a little difference is when I put the new injectors in it. I thought the long start time was normal too. I changed every sensor, including the injectors and did a full tune up and no change. Then I put a new cable from the negative terminal on the battery to the engine with a second wire going from that same terminal to the fender and a "new" braided gound strap and voila.... Not only does the truck start as fast as a brand new car but it also fixed all my driveability problems, except maybe the fact that it sucks up gas like an alchoholic sucks up vodka. Link to comment Share on other sites More sharing options...
metrictonner Posted June 4, 2008 Share Posted June 4, 2008 Mine has done that since day one and I always took it as a blessing. The oil pump gets primed and the oil pooled in the bottom of the bearings gets a chance to coat the journals before a firing load is applied. I crank for a second or two. Stop. Then crank until it fires (another second or two). Sometimes a third second or two crank is necessary. Total time: 3 or 4 seconds. Link to comment Share on other sites More sharing options...
BLHTAZ Posted June 4, 2008 Share Posted June 4, 2008 Yeah...I forgot about that...replacing the battery harness did make a little difference on mine too., but it still cranks over 4-5 times before firing. Link to comment Share on other sites More sharing options...
Timmaay Posted June 7, 2008 Author Share Posted June 7, 2008 Ok switched out the cps and no dice, it didn't make a difference. any other things to try. Link to comment Share on other sites More sharing options...
comancheman Posted June 7, 2008 Share Posted June 7, 2008 no matter what you do i don't think u are really going to notice a difference. mine always took a long time to start until i put in new injectors which now sometimes it fires right up but 95% of the time its still a long crank. i suppose if your fuel pump isnt priming it would cause an abnormally long crank time. when u turn it to run do u hear it priming? Link to comment Share on other sites More sharing options...
89eliminator Posted June 7, 2008 Share Posted June 7, 2008 do be honest, don't waste your time trying to fix it. 3-4 seconds like you stated is normal. My 89 takes about 3 seconds, and my old 88 took about 5 seconds and they both run perfectly. Link to comment Share on other sites More sharing options...
Timmaay Posted June 8, 2008 Author Share Posted June 8, 2008 no matter what you do i don't think u are really going to notice a difference. mine always took a long time to start until i put in new injectors which now sometimes it fires right up but 95% of the time its still a long crank. i suppose if your fuel pump isnt priming it would cause an abnormally long crank time. when u turn it to run do u hear it priming? yea I can hear it priming. You guys are probably right I should just leave it alone, as long as it starts everytime. Link to comment Share on other sites More sharing options...
Eagle Posted June 8, 2008 Share Posted June 8, 2008 You have a choice here, between two competing philosophies: (1) If it ain't broke, don't fix it. (2) If it ain't broke, fix it 'til it is. Take your pick. In my experience, #1 is less expensive and less painful. Link to comment Share on other sites More sharing options...
chicofuentes0224 Posted June 8, 2008 Share Posted June 8, 2008 You have a choice here, between two competing philosophies: (1) If it ain't broke, don't fix it. (2) If it ain't broke, fix it 'til it is. Take your pick. In my experience, #1 is less expensive and less painful. Everyone is going to agree with Eagle. Don't start spending money till the truck won't start or gives you drivability problems. Link to comment Share on other sites More sharing options...
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