anti-christ-comanche Posted November 2, 2012 Share Posted November 2, 2012 so this has been an issue since ive gotten the truck only the tach and spedo and mabey the battery light work? the fuel gauge bounces around the temp gauge sits in the blue the oil pressure gauge is stuck over to the right? but just today i was going into town and a friend passed me and he called me asking why i was driving so slow ( my spedo said i was going 65) when i get to about an indicated 68mph the little pointer thing starts jumping around. also is 4000rpm normal for a 86 2.5 4x4 in 5th gear going 55-60? one thing i do know is that my tires are not stock size...i have 235/75/15 now wich replaced 215/75s but talking to the guy i bought it from said that those wernt stock size either he just took them off his xj and put them on the mj...i got the build sheet from the door jamb and under tires it says 6374 whatever that means? mabey this shouldve been split up into multiple post idk...anything would be great Link to comment Share on other sites More sharing options...
gogmorgo Posted November 3, 2012 Share Posted November 3, 2012 Just going from the size of the tires themselves, a 235/75/15 has a 4% larger circumference than 215/75, but the larger tires should make your speedo read low, not high. I'd guess at lower than normal gears, assuming everything's indicating "properly". 4k seems a little high, but does your engine actually sound like it's revving that high? As for the speedo jumping around, that's likely an issue with the cable or something the cable connects too. I think I've seen a thread or two pertaining to that issue. My dad's van does that, but it's not really worth it to fix since it still points more or less in the right direction. What's up with the battery light? With normal driving, the fuel will slosh around, which can significantly change what the gauge reads. Mine goes up and down by a 1/4 tank accelerating and decelerating. Link to comment Share on other sites More sharing options...
jimoshel Posted November 3, 2012 Share Posted November 3, 2012 4000 is not normal. My '87 2.5 with 5 spd and 3;55 runs around 2000 RPM at 75MPH. A dry speedo cable will cause a jumping needle, as will a speedo going bad. Remove the cable clean and lube it. Re-install. Link to comment Share on other sites More sharing options...
Eagle Posted November 3, 2012 Share Posted November 3, 2012 so this has been an issue since ive gotten the truck only the tach and spedo and mabey the battery light work? the fuel gauge bounces around the temp gauge sits in the blue the oil pressure gauge is stuck over to the right? but just today i was going into town and a friend passed me and he called me asking why i was driving so slow ( my spedo said i was going 65) when i get to about an indicated 68mph the little pointer thing starts jumping around. also is 4000rpm normal for a 86 2.5 4x4 in 5th gear going 55-60? one thing i do know is that my tires are not stock size...i have 235/75/15 now wich replaced 215/75s but talking to the guy i bought it from said that those wernt stock size either he just took them off his xj and put them on the mj...i got the build sheet from the door jamb and under tires it says 6374 whatever that means? mabey this shouldve been split up into multiple post idk...anything would be great Assuming the stock tires might have been 215/75R15s (they were more likely 205s. but I don't have data for that size), so 60 MPH road speed with a 5-speed tranny should be just about 2320 RPM. Link to comment Share on other sites More sharing options...
anti-christ-comanche Posted November 6, 2012 Author Share Posted November 6, 2012 ok so lets focus on the tach and spedo...it is pretty loud but i called the friend that i bought the truck from and he said that the tach is operated threw the computer which he told me was the little yellow box under the dash and he said he replaced that but he also said that it may be one from a v6 but it says amc on it so i don't think so....how hard is it to remove the cable i can't find it in my book? Link to comment Share on other sites More sharing options...
Backdraft Posted November 6, 2012 Share Posted November 6, 2012 That little yellow box is the cruise control computer. Your ECM, or engine computer, is silver (aluminum) and sits upright under the dash to the right of the steering column. At least they are on 87 to 90 Renix models. Link to comment Share on other sites More sharing options...
anti-christ-comanche Posted November 7, 2012 Author Share Posted November 7, 2012 That little yellow box is the cruise control computer. Your ECM, or engine computer, is silver (aluminum) and sits upright under the dash to the right of the steering column. At least they are on 87 to 90 Renix models. my cruise doesnt even work haha..ya ik what your talking about it says renix on it... Just going from the size of the tires themselves, a 235/75/15 has a 4% larger circumference than 215/75, but the larger tires should make your speedo read low, not high. I'd guess at lower than normal gears, assuming everything's indicating "properly". 4k seems a little high, but does your engine actually sound like it's revving that high? As for the speedo jumping around, that's likely an issue with the cable or something the cable connects too. I think I've seen a thread or two pertaining to that issue. My dad's van does that, but it's not really worth it to fix since it still points more or less in the right direction. What's up with the battery light? With normal driving, the fuel will slosh around, which can significantly change what the gauge reads. Mine goes up and down by a 1/4 tank accelerating and decelerating. ok so now looking at the cluster i think the battery alternator gauge is fine but the oil pressure gauge is stuck over on high (80 i think) and ya the engine is very loud it almost sounds like the exhaust manifold is cracked or leaking or the exhaust is somewere near that but i checked that so ik thats not is Link to comment Share on other sites More sharing options...
cruiser54 Posted November 7, 2012 Share Posted November 7, 2012 Tach signal comes from the Ignition Control Unit. Green with tracer wire. Link to comment Share on other sites More sharing options...
cruiser54 Posted November 7, 2012 Share Posted November 7, 2012 If you have a cluster from a vehicle with gauges and a sending unit for the temp from a vehicle that doesn't have a gauge, you will not read right. Link to comment Share on other sites More sharing options...
anti-christ-comanche Posted November 8, 2012 Author Share Posted November 8, 2012 If you have a cluster from a vehicle with gauges and a sending unit for the temp from a vehicle that doesn't have a gauge, you will not read right. The cluster is all stock i have all the service records from previous owners i will go look to see if the sending unit was ever replaced i don't think that's it tho Link to comment Share on other sites More sharing options...
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