tarmac2dirt Posted July 2, 2021 Share Posted July 2, 2021 HI MJ owners, For those who have replaced there Crank sensor. Does any one have a preference on brand/ quality, or do they seem to be pretty much all the same quality. My MJ starts fine when cold but after a few miles, runs great shut it off and trying to restart it just cranks-cranks-cranks with no start. Heat maybe, i am in southern new mexico and its in the 100's every day. My thought is the cps, its orig as far as i know. Any thoughts about this?? Thanks Link to comment Share on other sites More sharing options...
JMO413 Posted July 2, 2021 Share Posted July 2, 2021 OEM is definitely the preferred. They can be a challenge to find but they are out there. Link to comment Share on other sites More sharing options...
tarmac2dirt Posted July 2, 2021 Author Share Posted July 2, 2021 Oh this is a 88 MJ with a 4.0 5sp Link to comment Share on other sites More sharing options...
scaleless Posted July 2, 2021 Share Posted July 2, 2021 I'm currently running a WVE 5S1800 to great effect. This is the High Altitude sensor, however. If you test it with an AC meter as Cruiser54 instructs in his tips, it outputs 400mV. Link to comment Share on other sites More sharing options...
jeeptec1 Posted July 2, 2021 Share Posted July 2, 2021 The cps is a very common failure part. Finding an OE is very hard to find. They are no longer made but some dealerships have them in inventory or someone has some nos stock. I would definitely start there. Also check your fuel pump output. They do get weak and have low pressure with age. Sent from my iPad using Tapatalk Link to comment Share on other sites More sharing options...
scaleless Posted July 2, 2021 Share Posted July 2, 2021 But before we go about replacing any parts, how about some tests? Check for fuel pressure and check for spark when the truck isn't starting. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 2, 2021 Share Posted July 2, 2021 An 87 huh? Has a C101 connector which reduces the signal from CPS to computer. I would replace NO PARTS at this point. Go to my website and complete Tips 1 through 5 FIRST! Link to comment Share on other sites More sharing options...
jeeptec1 Posted July 2, 2021 Share Posted July 2, 2021 An 87 huh? Has a C101 connector which reduces the signal from CPS to computer. I would replace NO PARTS at this point. Go to my website and complete Tips 1 through 5 FIRST!What’s your website?Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
scaleless Posted July 2, 2021 Share Posted July 2, 2021 18 minutes ago, jeeptec1 said: What’s your website? The, uh, gigantic, colorful link in his signature. Link to comment Share on other sites More sharing options...
ghetdjc320 Posted July 2, 2021 Share Posted July 2, 2021 16 hours ago, tarmac2dirt said: HI MJ owners, For those who have replaced there Crank sensor. Does any one have a preference on brand/ quality, or do they seem to be pretty much all the same quality. My MJ starts fine when cold but after a few miles, runs great shut it off and trying to restart it just cranks-cranks-cranks with no start. Heat maybe, i am in southern new mexico and its in the 100's every day. My thought is the cps, its orig as far as i know. Any thoughts about this?? Thanks Your problem sounds much more like a coolant temp sensor to me. It leans out the mixture when the engine warms up. If it’s failing, it can lean it to the point of no start. I’ll mention again that I’m no renix expert so I may be off on this. But coolant temp is a factor for enrichment on every efi system I’ve worked on. Link to comment Share on other sites More sharing options...
scaleless Posted July 3, 2021 Share Posted July 3, 2021 The coolant temp is a factor in fuel ratio, but it definitely wouldn't be enough to cause a no-start. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 3, 2021 Share Posted July 3, 2021 Correct. The TIPS need to be done first!! Here is an excerpt from Tip 1. The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, failed emission tests, and wasted money replacing components unnecessarily. All the components listed below ground at the dipstick tube stud: Distributor Sync Sensor, TCU main ground, TCU “Shift Point Logic”, Ignition Control Module, Fuel Injectors, ECU main ground (which other engine sensors ground through, including the Oxygen sensor, Knock Sensor, Cruise Control and Transmission Sync signal. All extremely important stuff. The factory was aware of the issues with this ground point and addressed it by suggesting the following: go to Tip 1 to find the fix. 10 minute job. An excerpt from Tip 2: The C101 connector on 1987 and 1988 Renix Jeeps was a source of electrical resistance when the vehicles were new. So much so that the factory eliminated this connector in the 1989 and 1990 models. The factory recommended cleaning this connector to insure the proper voltage and ground signals between the ECU and the fuel injection sensors. We can only imagine how this connector has become a larger source of voltage loss and increased resistance over a period of more than 25 years. The C101 connector needs to be cleaned at least once in the lifetime of your vehicle. Chances are it’s never been done before. Almost every critical signal between the engine sensors, injectors, ECU, and some to the TCU, travel this path through the C101 connector. That said, the cleaning described below is a real MUST DO right off the bat for any new-to-you Jeep. An excerpt from Tip 5: The sensor ground circuit affects the CTS, TPS, IAT, MAP, ECU and diagnostic connector grounds. It’s very important and not something to overlook in diagnosing your Renix Jeep as it is common for the harnesses to have poor crimps causing poor grounds. If any or all of the sensors do not have a good ground, the signal the ECU receives from these sensors is inaccurate. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 3, 2021 Share Posted July 3, 2021 9 hours ago, jeeptec1 said: What’s your website? Sent from my iPhone using Tapatalk www.cruiser54.com Link to comment Share on other sites More sharing options...
Eagle Posted July 3, 2021 Share Posted July 3, 2021 6 hours ago, ghetdjc320 said: Your problem sounds much more like a coolant temp sensor to me. It leans out the mixture when the engine warms up. If it’s failing, it can lean it to the point of no start. I’ll mention again that I’m no renix expert so I may be off on this. But coolant temp is a factor for enrichment on every efi system I’ve worked on. Nope. Bad CPS. Fails when heat soaked. Link to comment Share on other sites More sharing options...
ghetdjc320 Posted July 3, 2021 Share Posted July 3, 2021 2 hours ago, scaleless said: The coolant temp is a factor in fuel ratio, but it definitely wouldn't be enough to cause a no-start. It is on many vehicles Link to comment Share on other sites More sharing options...
ghetdjc320 Posted July 3, 2021 Share Posted July 3, 2021 42 minutes ago, Eagle said: Nope. Bad CPS. Fails when heat soaked. As I said, I’m no renix expert. However, generally, with efi, the cps provides for ignition timing only. It’s not used for fueling. So if the OP has a fueling issue then an out of range cts is a possible culprit. This is common with exponential rate cts sensor sweeps. If the cps fails when heat soaked then wouldn’t lightly spraying some water on the sensor get it going again? Same goes for the cts. Either way, we’re assuming that heat is the issue so accelerating the cooling of sensors may provide a quick diagnosis. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 3, 2021 Share Posted July 3, 2021 There's a priority list for dying, crank no start. CTS and IAT aren't on the list with Renix. And yes, I have seen folks pour water on the CPS and it comes alive. But, with Renix it is likely connections and/or grounds. Link to comment Share on other sites More sharing options...
ghetdjc320 Posted July 3, 2021 Share Posted July 3, 2021 2 hours ago, cruiser54 said: There's a priority list for dying, crank no start. CTS and IAT aren't on the list with Renix. And yes, I have seen folks pour water on the CPS and it comes alive. But, with Renix it is likely connections and/or grounds. Good to know . However, I believe the OP never mentioned it was dying. Only that when it was shutoff it would not crank back up until it cooled down. It sounds like, up until that point it was running fine even though it was hot/at operating temp. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 3, 2021 Share Posted July 3, 2021 I meant either one. Link to comment Share on other sites More sharing options...
tarmac2dirt Posted July 3, 2021 Author Share Posted July 3, 2021 Thanks for all the tips. i have done some of the ground cleaning. Will separate the 101 connector and clean it tomorrow, no time now to cut and solder each wire. Started right up this morning, drove to the bank and back home about 8miles total, shut it off and it did start right back up. I'll let the temp outside get up to 100 and try this afternoon. It runs great when it starts. i'll do some of 54 tips tomorrow if i get the chance. Thanks for tips and suggestions. Paul Link to comment Share on other sites More sharing options...
cruiser54 Posted July 3, 2021 Share Posted July 3, 2021 I cannot stress enough the need to COMPLETE the Tips. Link to comment Share on other sites More sharing options...
JMO413 Posted July 4, 2021 Share Posted July 4, 2021 9 hours ago, cruiser54 said: I cannot stress enough the need to COMPLETE the Tips. Link to comment Share on other sites More sharing options...
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