kaylor23 Posted August 27, 2009 Share Posted August 27, 2009 i have an 87 jeep comanche with a 4.0L that i just put a new engine in , but it runs like it has a miss and is extremely hard to start. I checked spark and its great, and took a test light and started to test if all my injectors had power to them. Come to find out my number two cylinder has no power. Ive traced the wire but can't find anything wrong but still do not have any power. Any ideas? Link to comment Share on other sites More sharing options...
wallisek Posted August 27, 2009 Share Posted August 27, 2009 If there isn't anything wrong with your wiring, sounds like a bad injector. With a new engine and the fact your injectors are over 20 years old, I'd either have them professionally cleaned or replaced with new ones. There is a way to test yourself by measuring ohms but I don't have the specs. Since x6 injectors can be a costly purchase I'd look at having them tested & cleaned. I had mine cleaned last year when I started to get a lot of random misfires on #6. I had them cleaned by Witchhunter and haven't had a problem since. Spent a little over $100 for cleaning and testing of all six injectors. New ones would have cost me over $300. http://www.witchhunter.com/ Hope you track your problem down. :cheers: Link to comment Share on other sites More sharing options...
kaylor23 Posted August 27, 2009 Author Share Posted August 27, 2009 i bought new ones and put them in after i started having this problem still didnt fix it. is there a sensor or something that controls when the injectors fire that could have gone out? Link to comment Share on other sites More sharing options...
jpdocdave Posted August 27, 2009 Share Posted August 27, 2009 it has nothing to do with the injector itself if its not getting power to it. this is a really weird one since you say the wiring is good, if just one isn't firing i'd have said its a pinched wire for it somewhere. the sensors that can effect the injector pulse will effect them all, such as a bad crank sensor, you won't have pulse on any injectors. it may be the signal from the pcm for that injector. its possibly a bad computer. Link to comment Share on other sites More sharing options...
kaylor23 Posted August 27, 2009 Author Share Posted August 27, 2009 yea i have no idea ive traced the wire all the way up to the map sensor tested it on both sides of the sensor no power so i kept tracing it all the way over to the other side of the engine compartment tested and still nothing. would a messed up computer do this for certain? Link to comment Share on other sites More sharing options...
Oizarod115 Posted August 28, 2009 Share Posted August 28, 2009 yea i have no idea ive traced the wire all the way up to the map sensor tested it on both sides of the sensor no power so i kept tracing it all the way over to the other side of the engine compartment tested and still nothing. would a messed up computer do this for certain? ... i may be wrong here but your fuel injectors should NOT be wired to the map sensor... they should be wired to the computer. and the map sensor should also be wired to the computer... :redX: Link to comment Share on other sites More sharing options...
Wildman Posted August 29, 2009 Share Posted August 29, 2009 Yes, the injectors are "fired" directly from the ECU. If you have no power to one or more injectors, it could be a bug in the ECU. That could also be causing your "very hard starting" problem too. Before you swapped this engine, did the original engine run???? Best thing is to get a good used ECU and swap that out before you go any further. If you have a pick-n-pull near you, or a good junk yard, try to find one of like year and the really only difference in all the ECU's ('87-'90) is either an automatic tranny or the manual transmission. If your near me, I'll loan you one to see it that's your problem :D Link to comment Share on other sites More sharing options...
Mongo Posted August 29, 2009 Share Posted August 29, 2009 I have the fuel injection manual for the renix system. It suggests to check the ground circuit to the injector that does not flash when a test lamp is attached while cranking. Still looking for the schematic that illustrates where that ground is. Link to comment Share on other sites More sharing options...
Mongo Posted August 29, 2009 Share Posted August 29, 2009 scratch that, they share a common ground. Power to the #2 injector comes from Pin A3 from the ECU connetor. Stick a light to that, crank the engine, if no pulse than I agree to check the ECU. Link to comment Share on other sites More sharing options...
aemsee Posted August 29, 2009 Share Posted August 29, 2009 I don't have a manual for an 87 but have one for a 90. In the 90 book the #2 injector wire at the ecu is connector A pin cavity #3, a light green wire. Might be the same for 87. Check at the ECU for power while cranking. You could have a wire that is broken inside without the plastic being visibly damaged. Link to comment Share on other sites More sharing options...
HOrnbrod Posted August 29, 2009 Share Posted August 29, 2009 I don't have a manual for an 87 but have one for a 90. In the 90 book the #2 injector wire at the ecu is connector A pin cavity #3, a light green wire. Might be the same for 87. Check at the ECU for power while cranking. You could have a wire that is broken inside without the plastic being visibly damaged. And if you have pulses from the ECU pin A3, then do a continuity check from the connector to the #2 injector end, and twist the connector back and forth slightly while doing it. Not uncommon for the wires to break off the pin internally in the connector, especially if the connector has been removed/reinstalled several times. :eek: Link to comment Share on other sites More sharing options...
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