benjy_26 Posted June 25, 2014 Posted June 25, 2014 Hello all. I've been working on a buddy's 94 ZJ and I've gotten myself into somewhat of a pickle. Initially, this vehicle would not rev past 4000rpm, developing a severe miss at this engine speed. It had a CEL, we ran the key test and fixed a few things, but a MAP sensor fault code was still present. I back probed the sensor and it showed the proper 5.0v. This truck has no cat, btw. We changed the fuel filter (ut was time to do so), and while attempting to check the CPS, the leads on it fell apart. We installed a new CPS.... and it won't start. The CPS shows open/infinite when probing the B and C terminal, but there's no spark coming out of the coil. I re-did the grounds, replaced the coil, pick up coil, cap and rotor (more maintenance), and the plugs. The dizzy was indexed a bit off, so I took care of that as well. No spark. I then swapped the horn relay with the ASD relay. The horn honks with either relay, but I still get no spark. My next step is to swap in a spare ECM I have lying about. Do you guys have any recommendations?
benjy_26 Posted June 26, 2014 Author Posted June 26, 2014 Ok, So I used a set of Nood lights Nd I'm getting injector pulses and i used a test light and I AM getting current at the coil connections when I open the key and when cranking. This rules out a bad CPS or ECM, correct?
benjy_26 Posted June 26, 2014 Author Posted June 26, 2014 True! ^^^ Didnt think of it. I stopped seeing the forest for the trees. Thanks, Don.
MJCARENA Posted June 26, 2014 Posted June 26, 2014 The CPS should not read infinite. Disconnect the CPS and hook your meter to it and crank the engine over. Should read around .5 volts AC while cranking.
benjy_26 Posted June 26, 2014 Author Posted June 26, 2014 The CPS should not read infinite. Disconnect the CPS and hook your meter to it and crank the engine over. Should read around .5 volts AC while cranking. On a 4.0 HO, the CPS should be open/infinite when checking resistance between the B and C pins.I now have spark coming out of the coil (Had a defective MSD Blaster SS on our hands). Now, I just need to properly index the dizzy (messed up the 1st time, apparently) and we should be golden.
benjy_26 Posted June 26, 2014 Author Posted June 26, 2014 BTW, No codes are present on the ECM aside from 12 and 55.
MJCARENA Posted June 27, 2014 Posted June 27, 2014 The CPS should not read infinite. Disconnect the CPS and hook your meter to it and crank the engine over. Should read around .5 volts AC while cranking. On a 4.0 HO, the CPS should be open/infinite when checking resistance between the B and C pins.I now have spark coming out of the coil (Had a defective MSD Blaster SS on our hands). Now, I just need to properly index the dizzy (messed up the 1st time, apparently) and we should be golden. Sorry, I thought it was the same as a Renix CPS.
benjy_26 Posted June 27, 2014 Author Posted June 27, 2014 The CPS should not read infinite. Disconnect the CPS and hook your meter to it and crank the engine over. Should read around .5 volts AC while cranking.On a 4.0 HO, the CPS should be open/infinite when checking resistance between the B and C pins.I now have spark coming out of the coil (Had a defective MSD Blaster SS on our hands). Now, I just need to properly index the dizzy (messed up the 1st time, apparently) and we should be golden. Sorry, I thought it was the same as a Renix CPS. No prob!
benjy_26 Posted June 27, 2014 Author Posted June 27, 2014 Ok... so it's running, but it has a low idle, a misfire, and it still won't rev past 4k. Any thoughts?
FrankTheDog Posted June 28, 2014 Posted June 28, 2014 Possibly not enough fuel pressure. My 92 XJ had the same symptoms and the hose on the fuel pump wasn't tight enough. Maybe the fuel pump is getting tired?
benjy_26 Posted June 28, 2014 Author Posted June 28, 2014 Maybe. I havent checked pressure. I ran the key off/on test and came up with faults in the pickup coil circuit, voltage to the MAP sensor being too high or low, and a fault in the O2 sensor circuit. I'll let y'all know what happens tomorrow.
FrankTheDog Posted June 28, 2014 Posted June 28, 2014 Check for bare wires going to the O2 sensor. 96 XJ I had the rear O2 sensor wires were rubbing on the driveshaft. Once they wore through it would run erratically.
benjy_26 Posted June 28, 2014 Author Posted June 28, 2014 Thanks for the tip, Frank. I'm diving in now. I'll come back with my findings.
benjy_26 Posted June 29, 2014 Author Posted June 29, 2014 Swapped MAP, O2. and indexed the dizzy. I had initially put his 4° advanced out of habit (I have a rather large cam on my 4.0) and we got..... NOTHING. Back to no start/no spark. Went to Oteiley's for a fresh CPS, and there's voltage to the coil's primary (green wire), but the secondary does not show that it's switching. Changed the ASD relay, still nothing. I'm about to swap PCM's in a minute just to see what happens. The funny thing is... it was running on Friday night. Hell, we drove it for a few miles and, despite some low RPM stumbling, it did fine.
HOrnbrod Posted June 29, 2014 Posted June 29, 2014 came up with faults in the pickup coil circuit,... Do you mean a sync sensor code 54? Check to see if the wires are correctly positioned in the shell detent exiting the distributor, i.e. not crushed by the cap. If okay, I'd swap out the sync sensor. I've had two of those go bad.
benjy_26 Posted June 29, 2014 Author Posted June 29, 2014 came up with faults in the pickup coil circuit,... Do you mean a sync sensor code 54? Check to see if the wires are correctly positioned in the shell detent exiting the distributor, i.e. not crushed by the cap. If okay, I'd swap out the sync sensor. I've had two of those go bad. Exactly the one! I'll look at it. Is there any way to check the pickup coil?
HOrnbrod Posted June 29, 2014 Posted June 29, 2014 There's no test procedure for it in the FSM. There are two types: One you have to pull the distributor to change the sync sensor, the other you don't. If you have what looks like the below (you should in a 94) then it's a no pull.
benjy_26 Posted June 29, 2014 Author Posted June 29, 2014 Yeah. I have the type where the only thing that needs to be pulled is the cap.
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