bilgamesh Posted November 20, 2008 Share Posted November 20, 2008 I am pretty new to my 1990 model with a 4.0L automatic. It runs really well, but I am working through some quirks: 1. About half the time I go to start it, it cranks a few revs, turns over and revs up like it is starting normally, then dies. On the second, third or fourth try, I can rev the engine at startup, and it stays running, and runs fine from then on. As an added bonus, it has died twice on me, both at low speed or a light, seemingly spontaneously. I have seen various threads about the IAC, TPS and MAP. I guess what I am unclear on is how I can go about scientifically determining the problem without throwing each of these parts at it in sequence. 2. My blower only works when the lever is in the vent position. If I have it on heater, I can hear the blower motor running, but it is not pushing air out the vents. Incidental to this is the fact the A/C does not work, but I am not ready to tackle that yet. I would appreciate any guidance you can offer on these topics. Thanks, Bill Link to comment Share on other sites More sharing options...
jtdesigns Posted November 20, 2008 Share Posted November 20, 2008 You have any old gas in it?? I would do a fuel pressure check first off to make sure pressure is up and everything is working in the fuel delivery dept. Then I would goto the TPS and do the checks for voltage. Then I would remover the AIC and clean it good, Then if it was still doing it I would check for any vacuum leaks and vacuum blockages. # 2 even makes me want to say you have a vacuum issue. Or maybe the flapper door is stuck Jeepco had something like that happen to his truck I think, maybe he can explain what exactly the problem was.. Link to comment Share on other sites More sharing options...
maddzz1 Posted November 20, 2008 Share Posted November 20, 2008 This page will show you how to test all the sensors: http://www.lunghd.com/Tech_Articles/Eng ... ostics.htm Link to comment Share on other sites More sharing options...
bilgamesh Posted November 20, 2008 Author Share Posted November 20, 2008 Thanks, that one is thorough. Link to comment Share on other sites More sharing options...
Eagle Posted November 20, 2008 Share Posted November 20, 2008 2. My blower only works when the lever is in the vent position. If I have it on heater, I can hear the blower motor running, but it is not pushing air out the vents. If you can hear the blower running, then the blower is working. With the lever set to the HEAT position, no air should come out the dash vents. All air is directed to the feet, through the under-dash outlets. If you expect hot air through the face-of-dash outlets when the control is set for HEAT, you haven't read the owner's manual. The a/c isn't working in my '88, either (low freon, so the compressor won't kick in), so I use the BI-LEVEL setting to get heat to both my feet and through the dash vents. It is possible that you have a vaccum leak in the controls. The flappers that direct air are controlled by vacuum motors. If you have a vacuum leak, their default setting is to push air to the top-of-dash DEFROST outlets. If you can't feel air coming from anywhere else, check there. Link to comment Share on other sites More sharing options...
Pete M Posted November 20, 2008 Share Posted November 20, 2008 If the Jeep fires up and runs, then dies after a couple seconds, it could be a problem with the fuel pump resistor. It's the whit/gray ceramic block on the drivers side fender with 2 wires running to it. The pump gets direct current for a couple seconds, then power is switched by the computer and fed through the resistor (it lowers the voltage slightly to reduce pump noise). Try pulling the wires off the resistor and connecting them directly together (don't worry, you can't hurt anything. 1987 MJs didn't even have it yet). Link to comment Share on other sites More sharing options...
bilgamesh Posted November 20, 2008 Author Share Posted November 20, 2008 If you expect hot air through the face-of-dash outlets when the control is set for HEAT, you haven't read the owner's manual. Gee, I wish I had an owner's manual to read... Thanks for the info all the same When it is acting up it does not run for 2 seconds, more like 1 second. Thanks guys! Link to comment Share on other sites More sharing options...
Pete M Posted November 20, 2008 Share Posted November 20, 2008 I've never gotten an owners manual with an MJ (and I've purchased 5 over the years). :( They are on eBay though. :thumbsup: And I don't know exactly how many seconds the truck will run without the resistor. Could be 1. :dunno: Link to comment Share on other sites More sharing options...
mvusse Posted November 21, 2008 Share Posted November 21, 2008 That's not the headlight relay, it's the fog light relay. Link to comment Share on other sites More sharing options...
Eagle Posted November 21, 2008 Share Posted November 21, 2008 That's not the headlight relay, it's the fog light relay. DING! :thumbsup: We have a winnah! No relay for the headlights. Link to comment Share on other sites More sharing options...
bilgamesh Posted November 23, 2008 Author Share Posted November 23, 2008 My problem seemed a little more recurrent today. At times it took 5 or more attempts to start. The engine turns over, fires and revs to 2000 rpms, and then revs back down and dies. It died at a stoplight once too, and it took several tries to get it to turn over again. Re: Fuel Pump Ballast Resistor: Without cutting into the wires, I tried to jumper them, but I was not certain of a good connection. It seemed to help, but I am not 100% sure. The connectors and terminals on the resistor are both a little corroded. Tomorrow I plan to clean both up really well and test the resistance. Re: Owner's Manual: I was able to pick one up yesterday on ebay courtesy of our friend BLHTAZ. Re: Blower: It was cold here today, so I had occasion to try out the heater. Even though my manual has not arrived, thanks to Eagle, I now know that I should not expect heat to blow out the dash vents. I did confirm it will blow out on Bi-level. Thanks all, and I would still appreciate any more expertise and feedback on any of this. Link to comment Share on other sites More sharing options...
Sugarfoot Posted November 23, 2008 Share Posted November 23, 2008 Also check your wires entering the fuel pump at the gas tank. Look over the wires real well to check if they are shorting to each other. Ones orange I think and the other is black. Mine had rubbed a 1/4 inch of insulation off between them and would make contact and cause it to run strange, or not start at all. Once under way the wind under the truck would seperate them and the problem or weakness in performance would go away. Drove me nuts for a while. I knew it was a fuel problem though. Ordered a new pump and in the process found the problem with the wires. I had already dropped the tank so I went ahead and replaced the pump, sanded up and painted the tank to preserve it and put some liquid tape on the wires and rewrapped. Yee HA GO HORNS!! Link to comment Share on other sites More sharing options...
bilgamesh Posted November 23, 2008 Author Share Posted November 23, 2008 I cleaned up the connections real well on the ballast resistor, and jumpered across the wires. Either way it was the same. I also checked all the wiring to the fuel pump, ground and battery connections. I really don't think this is a fuel problem. It would really be more precise to say about half the time when starting, the engine will rev. as if it is going to start, then dies, no sputtering, just rev up, then die. It doesn't really run for any length of time. It will do this 2-6 times, then start okay 2-6 times. On the rare occasion it dies at lights, it also does not sputter, just dies outright. I guess I will have to dig into the troubleshooting of the CPS, IAC, TPS, EGR etc. Link to comment Share on other sites More sharing options...
Pete M Posted November 23, 2008 Share Posted November 23, 2008 Check the ground located behind the drivers side tail light. Link to comment Share on other sites More sharing options...
bilgamesh Posted November 23, 2008 Author Share Posted November 23, 2008 Check the ground located behind the drivers side tail light. Removed tail light assembly and confirmed small ground behind it was firmly attached. Thanks, Bill Link to comment Share on other sites More sharing options...
Pete M Posted November 23, 2008 Share Posted November 23, 2008 Did you clean up the connection? Link to comment Share on other sites More sharing options...
bilgamesh Posted November 23, 2008 Author Share Posted November 23, 2008 Removing and cleaning up that connection sounds like a long shot, but I will assume you know much I do not, and give it a shot. In the meantime, I removed the IAC again, sprayed some WD40 in it and gave it a good twist. Once I replaced it, the idle seems a little higher and I have not had the starting problem. I am cautiously optimistic this is the part that may be having problems. I will report back more later. The idle speed has always seemed low to me, around 400, but stable. I am going to search now for what the idle speed should be. Link to comment Share on other sites More sharing options...
bilgamesh Posted November 25, 2008 Author Share Posted November 25, 2008 Two days in a row with no starting problems after tinkering with the IAC valve. Link to comment Share on other sites More sharing options...
JeepcoMJ Posted November 25, 2008 Share Posted November 25, 2008 # 2 even makes me want to say you have a vacuum issue. Or maybe the flapper door is stuck Jeepco had something like that happen to his truck I think, maybe he can explain what exactly the problem was.. nah, I had a similar problem, but mine was the valve block on the back of the heater controls. he has a simple issue of not building vacuum. if the vacuum canister is connected properly, and he's been moving the controls without the engine running, he has no stored vacuum. so, he just needs the truck to run again, and he won't have any problems. well, that's most likely. after that, check the vacuum canister and probably replace the vacuum lines...they get brittle with age. Link to comment Share on other sites More sharing options...
BLHTAZ Posted November 26, 2008 Share Posted November 26, 2008 When seeming normal...mine has always idled around 700 - 800 Link to comment Share on other sites More sharing options...
bilgamesh Posted November 27, 2008 Author Share Posted November 27, 2008 Thanks for all the feedback. After 3 days of perfect starts, I had my first relapse today. This morning it cranked up and then down once, then started normally. Later in the day, it repeated three times before starting. Still baffled I guess... Link to comment Share on other sites More sharing options...
bilgamesh Posted December 2, 2008 Author Share Posted December 2, 2008 It took me awhile to connect the two, but I think it is the same problem he describes here: http://www.jeepsunlimited.com/forums/sh ... p?t=916973 If I keep the starter engaged, the truck stays running. My ignition switch is doing other strange stuff too, like not quite turning off the accessories, even with the key removed, and letting me remove the key while it is running. It is my plan to replace the ignition switch and/or cylinder unless I hear any helpful dissent. Thoughts anyone?... Thanks, Bill Link to comment Share on other sites More sharing options...
BLHTAZ Posted December 3, 2008 Share Posted December 3, 2008 The switch is definite a possibility, but the cylinder will have nothing to do with electrical function. I have posted and Electrical Manual & the FSM in the DIY forum if you care to download them and have them in your computer... Electrical post - viewtopic.php?f=9&t=12734 FSM post - viewtopic.php?f=9&t=12517 Link to comment Share on other sites More sharing options...
FxRacing282 Posted December 4, 2008 Share Posted December 4, 2008 It took me awhile to connect the two, but I think it is the same problem he describes here:http://www.jeepsunlimited.com/forums/sh ... p?t=916973 If I keep the starter engaged, the truck stays running. My ignition switch is doing other strange stuff too, like not quite turning off the accessories, even with the key removed, and letting me remove the key while it is running. It is my plan to replace the ignition switch and/or cylinder unless I hear any helpful dissent. Thoughts anyone?... Thanks, Bill my toyota, i can take the key out while driving. no biggie, BUT, if your colum is coo-koo i tend to find up here in the rust best is poor grounds and more poor grounds. say do you have an aftermarket sterao? i had a similar problem with mine and it turned out to be a wire shorting on the dash for the radio. Link to comment Share on other sites More sharing options...
carnuck Posted December 5, 2008 Share Posted December 5, 2008 I had trouble with my fuel pump relay. Swapped it around with the other one and starting/running probs went away! Link to comment Share on other sites More sharing options...
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