WahooSteeler Posted July 12, 2020 Share Posted July 12, 2020 Got in the truck yesterday with my son driving (his daily for the summer) and when first accelerating it bucked and/or missed a couple of times under light throttle. I asked if it had been doing that often and he said it did it a few times on Friday evening AFTER he put a few gallons of gas in at a Shell station. We had a short trip (@10mins) to our destination with speeds up to 55mph and no more missing the rest of the way. Parked it for about an hour, then he got in it, started no problem, drove it @10mins to a friends house with no issues and parked it. Started it once a few hours later to move it, wasn't running more than 30 seconds, no issues. He gets in it this morning to come home, turns over but no fire. I drive over to his friends house, lift the hood looking for fuel maybe around injectors, supply line and regulator, looks clean. Get under the truck and have him turn ignition on, hear the fuel pump turn on. No visual or smell of fuel around tank, FSU or filter. Within the last 3yrs, the following items have been replaced, not necessarily in this order: Rebuilt FSU by TriStarr Spectra JP4B tank (which I believe is baffled) Fuel Filter (external in-line) Fuel rail supply line O-ring and connector Plugs, wires, distributor Coil IAC TPS Mopar O2 Sensor Mopar 89-90 ECU Bosch 746s Link to comment Share on other sites More sharing options...
JustEmptyEveryPocket Posted July 12, 2020 Share Posted July 12, 2020 6 minutes ago, WahooSteeler said: turns over but no fire This statement, along with hearing the fuel pump, would have me checking the CPS output on cranking. If you have it, put an inline spark checker on it as well. Report back with results to that. Link to comment Share on other sites More sharing options...
WahooSteeler Posted July 12, 2020 Author Share Posted July 12, 2020 4 hours ago, JustEmptyEveryPocket said: This statement, along with hearing the fuel pump, would have me checking the CPS output on cranking. If you have it, put an inline spark checker on it as well. Report back with results to that. 240+ resistance on CPS, and ACV went from 0 to 0.01 when cranking. Haven't checked for spark yet.... Link to comment Share on other sites More sharing options...
JMO413 Posted July 12, 2020 Share Posted July 12, 2020 With that for a reading I'm fairly sure you don't need to check for spark beacuse there will be none. AC voltage should be .5 volts. http://cruiser54.com/?p=50 Link to comment Share on other sites More sharing options...
JustEmptyEveryPocket Posted July 12, 2020 Share Posted July 12, 2020 Yup. At this point CPS replacement is needed. FWIW I got my replacement CPS from Napa (ordered two at a time in case one was a dud). The first one I installed worked great. Something like .45VAC, and has been working for ~1.5 years now. YMMV I also highly recommend taking the exhaust off the manifold, removing the rear driveshaft, and dropped the transmission crossmember as much as you can to gain space to remove and install the CPS. Total work time for me was FAR less this way that trying to wrangle all of it in place. Although I have arms like a gorilla and fingers like sausages. Its amazing how far the engine will rotate safely doing it this way, and how much room you gain to access that stupid sensor. Link to comment Share on other sites More sharing options...
WahooSteeler Posted July 12, 2020 Author Share Posted July 12, 2020 Went back and double checked to be sure, still not showing anything above .01 ACV. Found an OEM CPS and ordered, will be here this week. I also have an exhaust leak that's been slowly getting worse, haven't found the location but almost certain its a cracked manifold. I recently picked up an HO exhaust manifold with the expansion pipes for cheap, so this may work out by being able to kill two projects with one tear down and much better access to the CPS. Link to comment Share on other sites More sharing options...
WahooSteeler Posted July 12, 2020 Author Share Posted July 12, 2020 One more thought to throw out there, I also recently upgraded the ECU to an 89-90 unit, can this cause the CPS to show a low voltage reading? I still have my OE ECU, I'll go plug that in to see if anything happens. Link to comment Share on other sites More sharing options...
JustEmptyEveryPocket Posted July 13, 2020 Share Posted July 13, 2020 56 minutes ago, WahooSteeler said: upgraded the ECU to an 89-90 unit, can this cause the CPS to show a low voltage reading Negative. If you are reading at the CPS terminal itself then the only thing in the mix is the CPS and the wires going to it. I guess also your voltmeter, but we will assume you checked it for good working operation before hand. If you are measuring the CPS input into the ECU, then you might have further issues. So to totally answer this question, we need to know where and how you are checking for VAC from the CPS. But I would bet you are reading at the main CPS connector located at the rear of the intake manifold. If thats true, then the only thing it can be is the CPS. R&R time. Link to comment Share on other sites More sharing options...
WahooSteeler Posted July 13, 2020 Author Share Posted July 13, 2020 3 minutes ago, JustEmptyEveryPocket said: I would bet you are reading at the main CPS connector located at the rear of the intake manifold. If thats true, then the only thing it can be is the CPS. R&R time. Correct, backprobing at the CPS connector with digital meter. It's a HF cheapie, but it's fairly new and did the trick on adjusting my TPS recently. Thanks everybody....... Link to comment Share on other sites More sharing options...
cruiser54 Posted July 13, 2020 Share Posted July 13, 2020 Check to see if your exhaust leak is heating up/melting the CPS wires. Link to comment Share on other sites More sharing options...
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