aerocorey Posted February 26, 2008 Share Posted February 26, 2008 I've been having an intermittant no start. When it runs it does fine, but when you shut it off it won't start again unless you let it sit for 30 minutes or so. I've been into full size Wagoneers for awhile now, and if this happened on a Wag I would have replaced the ignition module in a heartbeat. I got some good suggestions on here saying I should start with a CPS and then try a coil. I've replaced the CPS, coil, cap and rotor, and I've tested and inspected the plugs and wires. It's still happening. Other than battery cables and grounds all I can think of that's left to try is the module. I borrowed a spark tester and I'm not making spark at the coil. The battery cables don't look great, but all the accessories work fine, it cranks, and when it runs it goes until I shut it off. I'm not making a weak spark, I'm naking no spark at all. Is the module a waste of time? It's killing me that I haven't replaced it already, but that's alot of money. Link to comment Share on other sites More sharing options...
Randy in Maine Posted February 26, 2008 Share Posted February 26, 2008 Have you tested the Hall Effect Sensor? Link to comment Share on other sites More sharing options...
Eagle Posted February 26, 2008 Share Posted February 26, 2008 Randy, are you referring to the cam position sensor in the distributor? I would check that, too. I would also check the wiring leading to the ignition module to see if you're getting any flow in. If there's no 12-volts arriving at the coil/ignition module, then there's nothing for the coil to bump up to 70,000 volts or whatever the coil sends to the plugs. Link to comment Share on other sites More sharing options...
Randy in Maine Posted February 27, 2008 Share Posted February 27, 2008 Sorry I am afraid my terminology is dated. :oops: Link to comment Share on other sites More sharing options...
aerocorey Posted February 27, 2008 Author Share Posted February 27, 2008 Have you tested the Hall Effect Sensor? Are you referring to the magnetic trigger wheel in the dostributer? No, I haven't yet. I don't really suspect that as the problem because when it runs it runs well. It doesn't die. It just won't start again for 30 minutes after I shut it off. Am I overlooking something about the way the trigger wheel operates? I'm honestly a little confused about what a trigger wheel would actually do since there's a crank sensor. Does it just compare the crank and cam position for the ECM to provide more accurate timing information to keep things running smoothly as the timing set wears? I would also check the wiring leading to the ignition module to see if you're getting any flow in. If there's no 12-volts arriving at the coil/ignition module, then there's nothing for the coil to bump up to 70,000 volts or whatever the coil sends to the plugs. I haven't really looked at the wiring diagrams too hard yet, but on a Wagoneer there are 2 seperate logic pathways for cranking and running. If these trucks are like that too I wonder if the cranking circut in the module has problems switching properly when the module is hot. There's an ECM on this too, right? I almost suspect that an ECM on this would do more of the work that I'm associating in my head with the ICM on a Wagoneer. This learning curve is killing me. I've finally landed for a few weeks on my road trip so I'll bust out the mulitmeter and start shooting wires tomorrow. I need to make sure the cranking voltage is making it to where it needs to. I've also given the starter relay a few taps, but I didn't figure that would do much since it always cranks, just doesn't light off. I'd love it if someone could point me to some better online diagrams. Link to comment Share on other sites More sharing options...
aerocorey Posted February 28, 2008 Author Share Posted February 28, 2008 Messed with it some more and looked at the diagrams. I wasn't able to get the truck to not start all day today, so I didn't get much troubleshooting done. Looking at the diagram makes me think the ECM does most of the work I've come to think of an ignition module doing. Seems like the ignition module isn't anything more than a socket that the coil plugs into on this truck. does it really ever go bad? The ignition module gets 12V to the same pin straight from the ignition switch during cranking and running. The signal for advancing timing during cranking goes to the PCM. If the no-start happens again I'll test for 12V during cranking at the ignition module. If it's not there I'll check wiring, maybe replace the ignition switch. If there's 12V at the ignition module I'll check for 12V at the correct pin on the ECM plug. If there's 12V there I suppose I should try a new PCM. Thoughts? Please? Link to comment Share on other sites More sharing options...
Eagle Posted February 28, 2008 Share Posted February 28, 2008 Messed with it some more and looked at the diagrams. I wasn't able to get the truck to not start all day today, so I didn't get much troubleshooting done. Looking at the diagram makes me think the ECM does most of the work I've come to think of an ignition module doing. Seems like the ignition module isn't anything more than a socket that the coil plugs into on this truck. does it really ever go bad? The ignition module gets 12V to the same pin straight from the ignition switch during cranking and running. The signal for advancing timing during cranking goes to the PCM. If the no-start happens again I'll test for 12V during cranking at the ignition module. If it's not there I'll check wiring, maybe replace the ignition switch. If there's 12V at the ignition module I'll check for 12V at the correct pin on the ECM plug. If there's 12V there I suppose I should try a new PCM. Thoughts? Please? Yeah. Start by learning the correct terminology for the year vehicle. I don't mean to be rude -- I'm trying to point out you're going to confuse yourself, and everyone you ask about this problem. The 90 Jeep 4.0L engine (as well as the 2.5L, in fact) is what is referred to as a Renix system. "Renix" is short for Renault-Bendix, because those two companies collaborated on the design of the system back when Renault had a major stake in AMC-Jeep. Your '90 is the last year of the Renix ignition/injection system. You do not have a PCM. You do not have an ECM. You have a crankshaft position sensor (which is universally referred to as the CPS), a camshaft position sensor (which is what you are referring to as the trigger wheel in the distributor, but unlike an older transistor ignition system this one doesn't generate the spark, it only tells the engine if each cylinder is on a compression stroke or an exhaust stroke), an ignition control module, and an ECU (Engine Control Unit). The ignition module does perform some functions, and if it goes bad (which is rare) it will result in no spark. ECU failure is very rare, but possible. By far the most prevalent cause of no starts, bad running/skips, and intermittent no starts is the CPS -- the crankshaft position sensor. Or the wiring for it -- the wire runs VERY close to the manifold, and if not properly routed can easily have the insulation burned off and short out on the manifold. Link to comment Share on other sites More sharing options...
aerocorey Posted February 28, 2008 Author Share Posted February 28, 2008 Eagle, thanks. I'm familiar with the different systems and what years they were used, but I'm clearly still a rookie at troubleshooting them. I thought the book I'm using referred to the ECU as an ECM. My bad. Honestly I find it confusing that the folks at Renix would name the ignition module as an ignition module. It seems to me to be little more than a giant socket for the coil to sit in. I'm sure my incorrect nomenclature is doing the same thing to you guys. I've replaced the CPS and inspected the wiring as suggested previously. The old CPS cheked good and the wiring was zip-tied away from the manifold. The new CPS is routed the same. I don't see how the cam position sensor could create the intermittant problem I'm having, but just because I don't see it doesn't mean it's not the problem. From what I see on the diagram I have the only 2 components in the system that care whether the key is in ON or START are the starter relay and the ECU. The starter relay is woking properly because the engine is cranking. I'm going to replace the battery cables and add a battery to chassis ground before anything else. If that doesn't fix it what would you suggest next? I'm running out of ideas. Link to comment Share on other sites More sharing options...
aerocorey Posted March 1, 2008 Author Share Posted March 1, 2008 I've replaced the battery cables, added a battery to chassis ground, replaced the ignition module, checked for 12V at the ignition module on the occasions it won't start (it checks good, I was testing the wrong yellow wire before), had the battery load tested, and even tried tapping the ECU with the toe of my boot when it won't start. Nothing has changed. Today it did it while I was facing downhill in a driveway. It was running fine and I shut it off to go in the house. I came out 5 minutes later and it wouldn't start, just cranked and cranked and cranked. It roll started like a champ. I still haven't checked the cam sensor because I don't have any procedures for checking it. The parts store in town doesn't even list that sensor. I don't see it on the diagram in my crappy book, but I do see a "sync sensor" that I don't know anything about. Is that the cam sensor? I guess I'd have to replace the whole distributer if it's bad. Which of the sensors on this thing have the power to keep the engine from starting? Will it keep running if any of them stop working while the engine is running? I had a Dakota once with a bad CPS. If it couldn't make contact with the CPS while it was off it wouldn't start, but if it lost contact while it was running it wouldn't stop until i turned it off. I realize this is a diferent system, and I've already replaced the CPS, but it makes me wonder. Other than the cam position sensor I'm still out of ideas other than the starter relay and the ECU. Link to comment Share on other sites More sharing options...
chicofuentes0224 Posted March 1, 2008 Share Posted March 1, 2008 Corey, I can't remember, but did you check the fuel pump ballist resistor on the inner side drivers side fender. And by roll start do ya mean "pop the clutch" because wouldn't that just mean your starter is shot? Link to comment Share on other sites More sharing options...
aerocorey Posted March 1, 2008 Author Share Posted March 1, 2008 Corey, I can't remember, but did you check the fuel pump ballist resistor on the inner side drivers side fender. And by roll start do ya mean "pop the clutch" because wouldn't that just mean your starter is shot? I didn't do anything with the puel pump ballast resistor. Should I? When it doesn't start it cranks just fine, meaning that the starter engages and the engine turns over but there's no spark at the coil. Fuel pressure is good, just no spark. When I roll started it, yes, I just got it rolling and popped the clutch, sooo whatever was keeping it from starting wasn't enough to keep it from running once started. Ignition switch? It cranks fine so I doubt it. Starter relay? It cranks fine so I doubt it. Next time it does this I'll test for 12V at the wire that runs from the starter relay to the ECU for 12V, but the problem isn't that there's improper advance in the spark during cranking, it's no spark whatsoever during cranking. I've tried tapping this during cranking as well. ECU? I don't know a damn thing about them except that they apparently don't fail very often. Cam sensor? Don't know how to test it, would probably just replace the distributer and cross my fingers. Would love someone to tell me how to test this beast. Link to comment Share on other sites More sharing options...
maddzz1 Posted March 2, 2008 Share Posted March 2, 2008 When you turn the key to start does the truck start then stall when you release the key to run or does it just not start? Link to comment Share on other sites More sharing options...
aerocorey Posted March 2, 2008 Author Share Posted March 2, 2008 When you turn the key to start does the truck start then stall when you release the key to run or does it just not start? Doesn't start at all, no spark whatsoever. If I went out there now it would probably start because it's been sitting. Once I start it and shut it back off it's a crap shoot whether it'll start back up or not. I can crank it for 2 seconds, 10 seconds, 20 seconds...no spark. Doesn't seem to matter how long I run it before I shut it off either, it decides when it wants to not start. If it doesn't start I can walk away from it for 15 minutes, then it'll fire right up. I used it to drive from OH to VT last week. It ran on the highway without stopping through each tank of gas, then sat dead at each fuel pump for 15 minutes before it would start again and drive through the next tank of gas. I see how that ballast resistor could make it stall after it's started. I do have good fuel pressure all the time though. I did replace the fuel filter just for good measure. I also thought I hit the jackpot earlier when I found the wiring for the cam sensor chafing on the engine block, but when I inspected it there was no damage and a good layer of electrical tape wrapping. I zip tied it in a better place just because it was there to be done. That was about 5 seconds before the previously mentioned roll start. Is this one stumping you guys yet like it is me? Link to comment Share on other sites More sharing options...
chicofuentes0224 Posted March 2, 2008 Share Posted March 2, 2008 http://www.alldatadiy.com/alldata/AFI~V ... /131771273 Link to comment Share on other sites More sharing options...
chicofuentes0224 Posted March 2, 2008 Share Posted March 2, 2008 On a side note, that truck doesn't have a neutral safety switch because it's a manual right? Link to comment Share on other sites More sharing options...
aerocorey Posted March 3, 2008 Author Share Posted March 3, 2008 Correct on the NSS. I might have struck gold tonight. Everyone says CPS, CPS, CPS. I keep unplugging it, cleaning the connector, inspecting the wiring, unplugging it, cleaning the connector... Tonight it did it again, but it had been several hours since I turned it off. I had my wife crank it while I jiggled (technical term) various electrical thingies (another technical term) under the hood. When I shook the CPS harness it started! I'm going to cut out the plug for the CPS and wire it directly with butt connectors and see if the problem goes away. I'll be stoked if this fixes it because I never stopped messing with the CPS harness even though I was confident that it wasn't the problem. Maybe a little persistance will win the day here... Link to comment Share on other sites More sharing options...
Randy in Maine Posted March 3, 2008 Share Posted March 3, 2008 Been here? http://www.lunghd.com/Tech_Articles/Eng ... Stator.htm Link to comment Share on other sites More sharing options...
aerocorey Posted March 3, 2008 Author Share Posted March 3, 2008 No I haven't been to that site. Thanks for it. Link to comment Share on other sites More sharing options...
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