parkia86 Posted July 19, 2013 Share Posted July 19, 2013 To get started I have an 87 Jeep Comanche Laredo with the 4.0L engine and 4x4. The transmission is the 3 speed auto. This morning the Comanche started up fine but about 2 minutes into the drive she just stalled out. This has happened before and I just put it in park and she fired right up. About 6 hours later I was going to lunch and she would not start. The engine was cranking and she would sputter a bit as if she wanted to start but she wouldn't. After about 10 min I sprayed some starter fluid into the intake, she didn't start the first time but after several tries and putting starter fluid in the intake she fired up and I got her home. This is the second time she has done this and now I fear it's permanent, a few hours after getting home I tried again and she still failed. Work to date: I replaced the fuel injectors and the air throttle valve about 1.5 years ago. I do not remember the last time I did plugs and wires and distro cap. Replaced all of the engine bay vacuum lines. The battery is less than 2 weeks old. Fuel filter was replaced 3 yrs ago. Odd symptoms: I hear a strange buzzing/hissing coming from the vicinity of the fuel pump(assuming its the circular thing on the fuel tank). I put my hands on the vacuum lines in the area and could not detect a leak. I had the car in a garage this winter and prior to taking it out I have never heard that sound from the fuel tank. Spraying carb cleaner will eventually get her started but takes multiple attempts. If the engine is warm she will start. I plan on checking the fuel pressure at the rail this afternoon... Any other tests i should do to narrow down the problem? Also, if it is a fuel pump issue how do i tell the size of my fuel tank? All of the pumps are for either 16 or 20 gallon tanks... i want to make sure i order the right part. Link to comment Share on other sites More sharing options...
ComancheKid45 Posted July 19, 2013 Share Posted July 19, 2013 Failing Crank Posistion sensor.....your issue is a loss of spark not fuel, I'm almost certian by how uve described it ;) Link to comment Share on other sites More sharing options...
parkia86 Posted July 19, 2013 Author Share Posted July 19, 2013 I just did an AC voltage test while trying to crank and the cps was giving off .223 VAC it looks like that might be the problem. How hard are they to replace? Link to comment Share on other sites More sharing options...
Geonovast Posted July 19, 2013 Share Posted July 19, 2013 I don't think it's the CPS, since he seems to be getting spark, but just sounds like an incredibly weak spark. I recommend doing the plugs, wires, and cap, as well as checking the condition of the main grounding strap from the back of the head to the firewall. Also never hurts to add the aux ground from the battery to the fender like the HOs got. Just an FYI, but your truck has a 4 speed auto, the AW-4. 4.0 never got a 3 speed auto. Am I the only one seeing his post riddled with links to eBay ads? Link to comment Share on other sites More sharing options...
Oddmodman Posted July 19, 2013 Share Posted July 19, 2013 If that's a serious question Geo, the answer is yes lol. I see no ads. Link to comment Share on other sites More sharing options...
dinghyboy Posted July 19, 2013 Share Posted July 19, 2013 Geo: there are 4 ebay links in his message. Never seen that before on this site. Gavin Link to comment Share on other sites More sharing options...
Geonovast Posted July 19, 2013 Share Posted July 19, 2013 Must be something on his end then that's infecting his posts. Link to comment Share on other sites More sharing options...
parkia86 Posted July 20, 2013 Author Share Posted July 20, 2013 I don't know why ads are showing up in my post I think it just associates the names of stuff with parts. It is not intentional. Anyway I am going to replace the cps tomorrow and if that doesn't work ill do a full tune up. But with the voltages being abnormal I think I might have found the culprit. The jeep still starts most of the time. Link to comment Share on other sites More sharing options...
Alexia Posted July 20, 2013 Share Posted July 20, 2013 The eBay links are showing up since parkia86 copied his post direct from the HTML output on his topic on JeepForum instead of the source of the post. JeepForum runs advertisements that link words to advertisements. I went ahead and removed them. Link to comment Share on other sites More sharing options...
Eagle Posted July 20, 2013 Share Posted July 20, 2013 My first guess is CPS. And, FWIW, a 4.0L does not have a 3-speed automatic transmission. It has a 4-speed AW4. Link to comment Share on other sites More sharing options...
parkia86 Posted July 20, 2013 Author Share Posted July 20, 2013 Also thanks for the correction on the transmission heh! Link to comment Share on other sites More sharing options...
1989 Eliminator Posted July 22, 2013 Share Posted July 22, 2013 I agree. Test and if so, replace the CPS with a Mopar part, not an auto parts store special. By small chance that weird hissing noise could be caused by the ballast resistor located right next to your air box. It is a ceramic looking piece That is what controls how much current goes to the fuel pump. Less resistance, more current, more fuel pressure since the pump is working harder. These used to go all the time on older Chryslers. Could need a replace... I still believe it is the CPS. Go to Cruiser54's renix tips in the DIY section. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 22, 2013 Share Posted July 22, 2013 I agree. Test and if so, replace the CPS with a Mopar part, not an auto parts store special. By small chance that weird hissing noise could be caused by the ballast resistor located right next to your air box. It is a ceramic looking piece That is what controls how much current goes to the fuel pump. Less resistance, more current, more fuel pressure since the pump is working harder. These used to go all the time on older Chryslers. Could need a replace... I still believe it is the CPS. Go to Cruiser54's renix tips in the DIY section. actually just more noise from the pump as it spins faster without the resistor. Fuel pressure is regulated by the fuel pressure regulator. The ballast resistors used on old chryslers and other old stuff was to allow 12 volts to the points on canking and reduce it to 8 volts on running so the points would last longer. Link to comment Share on other sites More sharing options...
1989 Eliminator Posted July 22, 2013 Share Posted July 22, 2013 I agree. Test and if so, replace the CPS with a Mopar part, not an auto parts store special. By small chance that weird hissing noise could be caused by the ballast resistor located right next to your air box. It is a ceramic looking piece That is what controls how much current goes to the fuel pump. Less resistance, more current, more fuel pressure since the pump is working harder. These used to go all the time on older Chryslers. Could need a replace... I still believe it is the CPS. Go to Cruiser54's renix tips in the DIY section. actually just more noise from the pump as it spins faster without the resistor. Fuel pressure is regulated by the fuel pressure regulator. The ballast resistors used on old chryslers and other old stuff was to allow 12 volts to the points on canking and reduce it to 8 volts on running so the points would last longer. Right, the pump works harder. I thought that was my issue too but it was my CPS Link to comment Share on other sites More sharing options...
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