dunnc1991 Posted May 30, 2015 Share Posted May 30, 2015 Working on getting this 91 back up to running status. Dropped the tank to check for debris, and replaced the fuel filter. That helped the starting issue, but now it's got a low, stumbling idle. Is this a TPS issue, or a fuel issue? I can hear the pump turn on and prime so I don't think the issue is there. Link to comment Share on other sites More sharing options...
cruiser54 Posted May 30, 2015 Share Posted May 30, 2015 Just because the pump makes noise, does not indicate it's providing the proper fuel pressure to the injectors. Link to comment Share on other sites More sharing options...
HOrnbrod Posted May 30, 2015 Share Posted May 30, 2015 Check for fault codes. http://comancheclub.com/topic/28111-reading-obdi-91-and-92-mj-fault-codes/ Link to comment Share on other sites More sharing options...
dunnc1991 Posted May 30, 2015 Author Share Posted May 30, 2015 I'll check for codes here in a bit. What's the best way to check the fuel pump? Pressure, voltage? Link to comment Share on other sites More sharing options...
Megadan Posted May 30, 2015 Share Posted May 30, 2015 Check the pressure at the fuel rail with a gauge. That would be the best way. Link to comment Share on other sites More sharing options...
dunnc1991 Posted May 30, 2015 Author Share Posted May 30, 2015 Fair enough Link to comment Share on other sites More sharing options...
dunnc1991 Posted May 31, 2015 Author Share Posted May 31, 2015 I've searched and found proper renix fuel pressure to be 30 psi at idle. Is this also correct for a HO motor? Link to comment Share on other sites More sharing options...
Fernando87mj Posted May 31, 2015 Share Posted May 31, 2015 no , the HO requires a higher psi I think , somewhere between 45-49 psi , hopefully someone can chime in to confirm this Link to comment Share on other sites More sharing options...
dunnc1991 Posted May 31, 2015 Author Share Posted May 31, 2015 no , the HO requires a higher psi I think , somewhere between 45-49 psi , hopefully someone can chime in to confirm this I thought I had read that, but can't find any source for it. Link to comment Share on other sites More sharing options...
HOrnbrod Posted May 31, 2015 Share Posted May 31, 2015 For 91-92 MJs with the stock non-adjustable regulator, fuel pressure should be 39 psi w/o vacuum, 31 psi w. vacuum. Link to comment Share on other sites More sharing options...
cruiser54 Posted May 31, 2015 Share Posted May 31, 2015 no , the HO requires a higher psi I think , somewhere between 45-49 psi , hopefully someone can chime in to confirm this I thought I had read that, but can't find any source for it. When they went to the returnless fuel injection system, the pressures were higher spec. comanche was discontinued years before that. Link to comment Share on other sites More sharing options...
dunnc1991 Posted May 31, 2015 Author Share Posted May 31, 2015 Ok, so fuel pressure was in check, and the only two codes I pulled were 12 and 41. Link to comment Share on other sites More sharing options...
Fernando87mj Posted May 31, 2015 Share Posted May 31, 2015 Thanks cruiser and hornbrod , learned something new :) Link to comment Share on other sites More sharing options...
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