CognizantPotato Posted July 28, 2020 Share Posted July 28, 2020 Hi all! I recently bought an 89 Comanche with the 4.0. I drove it about 70 miles home. When I was roughly 3 miles away from the house, the truck started bucking and then just quit. After I got it home, I was able to start the truck by wiggling the CPS Connector. I looked at the pins in the connector housing and saw that one of them was melted or bent. I got a replacement CPS (I think the brand was BWD) and installed it... still no start. I’ve since then replaced the ICM because it looked like it had overheated at some point, but that didn’t help either. I just tested the MAP sensor with the key in the on position and got around 1.5V - 2V from the b terminal. From everything I’ve seen online the MAP sensor should be around 5V. I’ve also tested the new CPS and its spiking to around .7V when cranking. I’m wondering if anyone has any tips for me, or anything I can do to try to further diagnose the problem. Link to comment Share on other sites More sharing options...
Ωhm Posted July 28, 2020 Share Posted July 28, 2020 48 minutes ago, CognizantPotato said: I just tested the MAP sensor with the key in the on position and got around 1.5V - 2V from the b terminal. I'll take it you backprobed the MAP sensor b terminal. Check vacuum hose between MAP and manifold for clogging. With the reading you got it could be trapped vacuum between clog and MAP. Take same reading with vacuum hose disconnected. Link to comment Share on other sites More sharing options...
CognizantPotato Posted July 29, 2020 Author Share Posted July 29, 2020 41 minutes ago, Ωhm said: I'll take it you backprobed the MAP sensor b terminal. Check vacuum hose between MAP and manifold for clogging. With the reading you got it could be trapped vacuum between clog and MAP. Take same reading with vacuum hose disconnected. I did backprobe the MAP sensor. The highest I’m reading right now with the hose hooked and unhooked is 0.35V Link to comment Share on other sites More sharing options...
Ωhm Posted July 29, 2020 Share Posted July 29, 2020 Backprobe C218_C. KEY ON. Looking for 5vdc. Link to comment Share on other sites More sharing options...
CognizantPotato Posted July 29, 2020 Author Share Posted July 29, 2020 25 minutes ago, Ωhm said: Backprobe C218_C. KEY ON. Looking for 5vdc. Yep. Just tested again with that procedure and it’s still reading low. I verified the multimeter is working correctly so it looks like it might be time for a new MAP sensor Thanks for the help Link to comment Share on other sites More sharing options...
Ωhm Posted July 29, 2020 Share Posted July 29, 2020 Just one more pin to check. Disconnect C218. KEY OFF. Measure continuity between C218_A and battery negative terminal. Link to comment Share on other sites More sharing options...
CognizantPotato Posted July 29, 2020 Author Share Posted July 29, 2020 21 minutes ago, Ωhm said: Just one more pin to check. Disconnect C218. KEY OFF. Measure continuity between C218_A and battery negative terminal. I just tested and there is continuity between terminal A and the negative battery terminal Link to comment Share on other sites More sharing options...
Ωhm Posted July 29, 2020 Share Posted July 29, 2020 32 minutes ago, CognizantPotato said: so it looks like it might be time for a new MAP sensor Link to comment Share on other sites More sharing options...
Eagle Posted July 29, 2020 Share Posted July 29, 2020 Did you test the output of the new CPS? Link to comment Share on other sites More sharing options...
CognizantPotato Posted July 29, 2020 Author Share Posted July 29, 2020 27 minutes ago, Eagle said: Did you test the output of the new CPS? I was getting spikes to around 0.7V when cranking. That’s pretty much all I tested on the new CPS. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 29, 2020 Share Posted July 29, 2020 Go to www.cruiser54.com and complete Tips 1,3,4, and 5 before anything else. Link to comment Share on other sites More sharing options...
CognizantPotato Posted July 29, 2020 Author Share Posted July 29, 2020 An update for today: I’ve checked the connection to the ICM and there is a full 12.5V going into it. There only seems to be around .75V to 1V leaving the ICM going to the ECU. I just replaced the ICM though, and the ECU was replaced very recently too. Is this small voltage normal, or does something sound wrong there? Link to comment Share on other sites More sharing options...
Ωhm Posted July 29, 2020 Share Posted July 29, 2020 45 minutes ago, CognizantPotato said: There only seems to be around .75V to 1V leaving the ICM going to the ECU. If were talking about the 2 pin connector at the ICM then that's timing input from the ECU (timing output). I don't know the values, but its a square wave signal based on dwell/spark triggering for the ICU's coil. Link to comment Share on other sites More sharing options...
CognizantPotato Posted July 29, 2020 Author Share Posted July 29, 2020 7 minutes ago, Ωhm said: If were talking about the 2 pin connector at the ICM then that's timing input from the ECU (timing output). I don't know the values, but its a square wave signal based on dwell/spark triggering for the ICU's coil. Ah okay that makes more sense now. Thanks! I’m replacing the MAP sensor tomorrow so I’ll update and let everyone know how it goes Link to comment Share on other sites More sharing options...
CognizantPotato Posted July 30, 2020 Author Share Posted July 30, 2020 Update: Installed the new MAP Sensor and still nothing I'm wondering if it’s not just a faulty cps still. I’m going to try and test it again Link to comment Share on other sites More sharing options...
CognizantPotato Posted July 30, 2020 Author Share Posted July 30, 2020 Still can’t get the engine to start. Any more ideas? Link to comment Share on other sites More sharing options...
Ωhm Posted July 30, 2020 Share Posted July 30, 2020 15 minutes ago, CognizantPotato said: Any more ideas? Using a voltmeter or testlight (preferred) check for B+ on the following pins (use battery negative terminal for ground): D1_5: B+ (Hot at all times) D2_4: B+ (Hot during KEY ON/CRANKING). D1_6: KEY ON (B+ (For 2-3 seconds)) or CRANKING (B+ (Hot during CRANK)). Link to comment Share on other sites More sharing options...
CognizantPotato Posted July 30, 2020 Author Share Posted July 30, 2020 25 minutes ago, Ωhm said: Using a voltmeter or testlight (preferred) check for B+ on the following pins (use battery negative terminal for ground): D1_5: B+ (Hot at all times) D2_4: B+ (Hot during KEY ON/CRANKING). D1_6: KEY ON (B+ (For 2-3 seconds)) or CRANKING (B+ (Hot during CRANK)). Okay I’m getting full voltage on D1_5 and D2_4 On D1_6 I’m getting about 10-11V while cranking Link to comment Share on other sites More sharing options...
Ωhm Posted July 30, 2020 Share Posted July 30, 2020 Voltage readings are normal. Good time for cruisers tips. Can you hear the fuel pump run for 2-3 seconds when KEY is cycled ON? On 7/29/2020 at 9:19 AM, cruiser54 said: Go to www.cruiser54.com and complete Tips 1,3,4, and 5 before anything else. Link to comment Share on other sites More sharing options...
CognizantPotato Posted July 30, 2020 Author Share Posted July 30, 2020 8 minutes ago, Ωhm said: Can you hear the fuel pump run for 2-3 seconds when KEY is cycled ON? Yep I can hear the fuel pump. I’ve checked the grounds too and cleared them off. I’m beginning to think the female side of the cps connector may have been damaged due to the deformation of the first CPS connector. Link to comment Share on other sites More sharing options...
Ωhm Posted July 30, 2020 Share Posted July 30, 2020 CPS has been known to cause NO SPARK, NO INJECTORS. Link to comment Share on other sites More sharing options...
CognizantPotato Posted July 31, 2020 Author Share Posted July 31, 2020 I tested the CPS again today. It was still spiking to 0.7V while cranking, but I kept getting infinite resistance between A and B. Could this be a problem or does that sound normal? If this isn’t the problem I might have to start tearing the wiring system apart and starting from scratch lol. Link to comment Share on other sites More sharing options...
JustEmptyEveryPocket Posted July 31, 2020 Share Posted July 31, 2020 Before resorting to that, pull a plug wire, put a spare plug in in, and ground it out against the block. Then have someone crank the truck. Look at the plug for a bight blue spark. If no spark present, suspect CPS. If spark is present move to fuel. Link to comment Share on other sites More sharing options...
CognizantPotato Posted July 31, 2020 Author Share Posted July 31, 2020 7 minutes ago, JustEmptyEveryPocket said: Before resorting to that, pull a plug wire, put a spare plug in in, and ground it out against the block. Then have someone crank the truck. Look at the plug for a bight blue spark. If no spark present, suspect CPS. If spark is present move to fuel. Thanks for the tip. I’ve tested for spark that way. I know it’s getting fuel. I’m a bit skeptical that a new CPS wouldn’t work straight out of the box, but I know how aftermarket parts can be (especially cheaper ones) Link to comment Share on other sites More sharing options...
JustEmptyEveryPocket Posted July 31, 2020 Share Posted July 31, 2020 3 minutes ago, CognizantPotato said: I know it’s getting fuel You have put a pressure gauge on it and verified at least ~30psi? I would also spend some time and load test your grounds. Both engine to ground and frame to ground. Missing or high resistance can cause all kinds of issues. Have you taken a look at cruiser54's tips for the Renix? If not, you really need to. Complete 1-5 right away. Link to comment Share on other sites More sharing options...
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