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Stock XJ Cherokee Tech. All XJ Non-modified/stock questions go hereXJ (84-01)
All OEM related XJ specific tech. Examples, no start, general maintenance or anything that's stock.
95 Cherokee 4.0L. I'm getting two check engine code 27s and have a rough running engine. I checked voltage at each injector plug with the key turned to on (not cranking the engine) and I get 7.1 volts at each injector. I also checked voltage on the positive wire (dark green and orange) right at the relay box and it also reads 7.1 V. Is this correct? I thought the voltage should be 12V? Tried swapping relays with the AC relay and I get the same thing 7.1V. Does the engine have to be running to read 12V?
I've checked each injector plug with a noid light and they all test good. I'm thinking all the injectors are just getting a low voltage causing the rough idle. Unplugging each injector individually with the engine running causes it to bog. So I can't single out any one injector.
If the engine isn't running, the PCM probably isn't engaging the the autoshutdown relay which provides the +12v to the injectors, ignition coil, and the alternator field coil. You checked the battery voltage directly to make sure you're meter is accurate (and set on DC instead of AC)?
so I checked the voltage at each injector. I have 7.1 volts at every injector. I traced the wire back to the ASD relay. Ignition switch on I have battery voltage on all pins except the one going to the injectors 7.1. Installed a new relay still no change. I stuck my voltmeter probe up in where the wire connects and moved it around with no change.How can I make this a better connection? – Bob DFeb 17 '16 at 2:28
I do not have battery voltage at the relay. I pulled the relay and checked the voltage at all four pins. I get battery voltage at the three I'm supposed to get it and I get 7.0 where there should be no voltage. If I am correct in assuming there should be no voltage at the pin going to the injectors There must be a short somewhere that the 7 volts is coming from. Am I correct? – Bob DFeb 18 '16 at 16:39
well live and learn. My engine has to be running for the relay to operate. With rpms I have battery voltage and am running smooth. I appreciate your info Ben. – Bob DFeb 18 '16 at 20:43
If you decide you need to replace injectors, pm JHC7399. He sells refurbished, tested, flow matched Bosch 4-hole injectors at a good price. The cheap chinese knockoffs from eBay are really poor quality and sometimes cause more problems then they solve.
Hey guys I really appreciate the responses. I checked the voltage at the relay box and each injector plug and got battery voltage with the engine running at each one (13.9V). Then I checked the resistance of each injector itself and got 15.7-16.1 ohms on each one. I'm not really sure how else to test the injectors. They seem to be working fine. I'm also now getting 3 code 27s from the check engine light.
I checked compression and it's all good. I have good spark on each cylinder also. Any ideas what I should check next? Again, I really appreciate the help.
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
Good voltage to the top, but what about the other side of the circuit? Check the main PCM ground. It's on the plate near the distributor where the main battery ground is located.
Mark, thanks for the tip. I pulled that ground apart and cleaned it up good, but no luck. Mine is a 1995 and looks a little different than that (only one wire going to the stud). I'm not sure if the pcm grounds there on all year models. Trying to find a schematic now.
Year: 1998 Classic (I'll get it running soon....) and 02 Grand
Model: Cherokee (XJ)
Engine: 4.0
AFAIK, that's where the PCM grounds on all years. I know it's there on my two 94s, and my 97 and 98. If you have only one wire there, it could have been hacked up by some PO.
Circuit Z12 connects to cavities 11 and 12 of the PCM. The Z12 circuit provides ground for PCM internal drivers that operate high current devices like the injectors and ignition coil. Internal to the PCM, the power (device) ground circuit connects to the PCM sensor return circuit (from circuit K4).
Dave, thanks for that info from the FSM. I was able to use it to find the injector wiring diagrams for the 95. I checked resistance between each injector plug and the corresponding cavity on the PCM plug 13,14,15,16,38 and 58 and got 0.5 ohms for each one. Then, I checked resistance between the 11 and 12 cavities and the ground stud Mark pointed out earlier. I also got 0.5ohms on both. To me this means each injector plug is getting the full battery voltage from the ASD and also good ground from the PCM, confirming my noid light test earlier. Do you think a clogged injector would throw a CEL 27 code? I noticed a couple of my injector plugs(wire harness side) were cracked/broken. Maybe I'm not getting a good connection between the plug and the injector. I've got some new pigtails coming in tomorrow so that I can replace them and try again. Might also try resetting the pcm.
I noticed a couple of my injector plugs(wire harness side) were cracked/broken. Maybe I'm not getting a good connection between the plug and the injector. I've got some new pigtails coming in tomorrow so that I can replace them and try again.
Do you think a clogged injector would throw a CEL 27 code?
Yanking and cleaning the injectors is cheap and easy, so certainly can't hurt. Just touch 'em with a 9-12V jolt (prolonged power could fry 'em) to open the gate and shoot some carb, throttle, MAP, whatever cleaner you got hanging around.
I believe a CPS or CKS could be the culprit too, but not enough to shoot the parts cannon. Test them.
Fuel Injector Voltage
