Spydie Posted February 20, 2017 Share Posted February 20, 2017 Alright, so I'm restarting this as I bought the truck and actually drove it a long distance to feel out everything. I have a few ideas of what's up but need more input before I start replacing sensors. While driving at low speed and low throttle input the Jeep backfires left and right and stutters. Even just pulling it into my garage a few feet its "jumpy" Getting on the expressway it builds up to about 45mph and then feels like it needs to pop so i let off, it will backfire and then continue to raise in speed. Every once in awhile i could get it to continue up without "popping." The engine was recently rebuilt by a shop with a new stage 2 head, stage 1 cam, stroked out .020" over. It also had the crank reground. I've been going though trying to find any vacuum seals but have not been able to find anything. I believe I am missing the egr solenoid but have to check when i get home to be sure. Any ideas are welcome, I just got the truck on Friday so I haven't done much but will be going through all of cruiser54's tips. Link to comment Share on other sites More sharing options...
omega_rugal Posted February 21, 2017 Share Posted February 21, 2017 are you sure the camshaft was installed correctly? backfiring means the intake is still open when the spark ignites the fuel... or the CPS is sendign the wrong signal... Link to comment Share on other sites More sharing options...
big66440 Posted February 21, 2017 Share Posted February 21, 2017 I'd start with the basics, make sure the line to your MAP sensor is plugged in correctly and not kinked or damaged as well as making sure your vacuum lines are in good condition and plugged where they should be. Check your intake/exhaust manifold bolts to make sure they aren't loose, make sure your sensor grounds at the dipstick stud as well as the ground strap towards the rear of the engine connected to the firewall are clean and tight ( Cruisers Renix tips). You should also make sure your throttle position sensor was adjusted properly, all these steps are very easy to do and shouldn't take long, good luck. Link to comment Share on other sites More sharing options...
Zambeezy Posted February 23, 2017 Share Posted February 23, 2017 I'd start with the basics, make sure the line to your MAP sensor is plugged in correctly and not kinked or damaged as well as making sure your vacuum lines are in good condition and plugged where they should be. Check your intake/exhaust manifold bolts to make sure they aren't loose, make sure your sensor grounds at the dipstick stud as well as the ground strap towards the rear of the engine connected to the firewall are clean and tight ( Cruisers Renix tips). You should also make sure your throttle position sensor was adjusted properly, all these steps are very easy to do and shouldn't take long, good luck. If I wanted to inspect my vacuum lines and make sure they're plugged where they should, is there some kind of guide or diagram I can follow? I don't know how I would know what's right and what's wrong since I've never done it before Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 23, 2017 Share Posted February 23, 2017 Invest in a Factory Service Manual set. Best friend you will ever have. Link to comment Share on other sites More sharing options...
big66440 Posted February 23, 2017 Share Posted February 23, 2017 There should be a white sticker with your vacuum diagram on the cowl ( upper firewall area ) near your brake booster. I would highly recommend Hornbrods advice of getting a factory service manual, they can be found on ebay for a decent price and come in EXTREMELY handy. Link to comment Share on other sites More sharing options...
Spydie Posted February 23, 2017 Author Share Posted February 23, 2017 Alright guys, going through everything here's what I found. Here's what it was doing,1.) Backfiring like crazy. Couldn't get on the gas without it popping.2.) Stuttering. When I'd get on the throttle at any speed it would stutter or shutter kind of hard to explain. It wouldn't even go up my driveway without doing it. 3.) Had the miss at 1700rpmish.Here's what I have found and fixed,1.) The spark plugs were not replaced when the engine was done and man were they bad. 4 of them were fouled.2.) TPS Sensor had one wire not reading. The pigtail on the wire harness was absolutely destroyed and the C output wasn't reading anything. Once i got it replaced and connected right, i was getting .03v when it needed .83, so that was an issue as well. 3.) The biggest, and honestly most mind boggling problem was the vacuum lines were all sorts of messed up, despite him having the hose diagram on the hood! He had the Map sensor running to a vacuum port on the fuel rail so both the map sensor and this port were sucking while nothing was blowing The fuel rail vacuum was needing air so bad that if you covered it with your finger it would shut off the truck. So i connected the Map sensor to the throttle body and ran a new hose for the fuel rail vacuum to the air box and got that squared away. Then I was looking some more and found that the line for the vacuum canister wasn't even hooked up so I reconnected that.So, now the MJ is running "smoothly" Idle is 100x better, I can now drive it up my driveway with no shuttering what so ever. Haven't had it backfire on me yet. Going to get it plated today so I can see how it handles on the road. It used to bog down around 45mph and not want to continue without backfiring. I'm hoping most of that will be solved with this. We're all honestly surprised it made it made the 80 mile journey home. Link to comment Share on other sites More sharing options...
big66440 Posted February 23, 2017 Share Posted February 23, 2017 Good to know you've made progress, I would very highly recommend spending a few hours doing cruisers Renix tips, they've improved my Comanches performance by leaps and bounds. Link to comment Share on other sites More sharing options...
Spydie Posted February 23, 2017 Author Share Posted February 23, 2017 Good to know you've made progress, I would very highly recommend spending a few hours doing cruisers Renix tips, they've improved my Comanches performance by leaps and bounds. I've been reading through them and will be, my goal was to just go over the general stuff that was easily checked this week. I'm really happy it's running better. Link to comment Share on other sites More sharing options...
Zambeezy Posted February 24, 2017 Share Posted February 24, 2017 Invest in a Factory Service Manual set. Best friend you will ever have. What's a decent price for a set? I'm seeing them for $75 shipped, used in average condition Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 24, 2017 Share Posted February 24, 2017 That's about the average price for a set, although quite often they go under $50. Link to comment Share on other sites More sharing options...
johnj92131 Posted February 24, 2017 Share Posted February 24, 2017 Getting a set of factory service manuals for $75 is like buying an oil well or a gold mine for just $75. You would not pass up a gold mine for that price would you? I have a full set of factory service manuals for each car I own, Including a couple I have had for more than 45 years and still use. Link to comment Share on other sites More sharing options...
Minuit Posted February 24, 2017 Share Posted February 24, 2017 The FSMs are worth their weight in gold. Absolutely essential, if only for wiring diagrams and nothing else. All of the other stuff is just icing on the cake. Good job diagnosing things instead of throwing parts at it! Link to comment Share on other sites More sharing options...
Zambeezy Posted February 24, 2017 Share Posted February 24, 2017 Awesome, I went ahead and bought them. Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 24, 2017 Share Posted February 24, 2017 Awesome, I went ahead and bought them. :thumbsup: Too bad Chrysler didn't make a FSM set for the XJ/MJ vehicles only instead of having to wade through all the 91 YJ and SJ stuff I don't need. Learning to navigate the FSM's takes some time, but it's a lot better than doing guesswork without them. Link to comment Share on other sites More sharing options...
Kerry Posted February 24, 2017 Share Posted February 24, 2017 What's great about the factory manuals is that while a Chilton/Haynes/etc. will tell you how to replace a part the factory manuals explain how the systems are designed to work so you know why you're replacing that part. They will not always troubleshoot for you but give you the information needed to correctly troubleshoot it yourself. The factory manuals for the Renix Jeeps are more difficult than the Chrysler ones to manipulate. Here's a few things that are good to know when shopping for them.... 1 - There was not a manual made for the 87 or 88 Comanche or Cherokee. The manuals for those two years were an 86 manual with 87 and/or 88 updates added on to the back of the books. It's difficult sometimes to tell them apart (on Ebay at least) as the updated ones are often listed as an 86. The updated ones also include factory service bulletins (TSB) that provide even more good information. 2 - The Cherokee and Comanche manuals are different sets (unlike Chrysler ones) and both are two volumes, Vol 1 is mechanical, Vol 2 is body. 3 - In addition to the two volume sets there are separate manuals for specific engines,transmissions, and transfer cases. These are not usually necessary unless you're rebuilding those components but there is one manual that is important and that is the Fuel Injection Manual. It explains how the Renix system works and how to diagnose and replace individual sensors. Chrysler later made their own version of the Renix system manual that provides even more pictures and info. If there's any errors or more to add I welcome any input. Link to comment Share on other sites More sharing options...
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