parkia86 Posted December 16, 2015 Share Posted December 16, 2015 Gentleman I just installed a 4.7L stroker engine in my 1987 jeep comanche and she is running very sluggish... seems like an old worn out jeep. My mechanic that did the install has tested every sensor, replaced the bad sensors... fuel pressure is in spec... etc... I called the tech service of the engine manufacturer and he suggested having the jeep tuned... Does anyone have any advice on how to go about this? Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 16, 2015 Share Posted December 16, 2015 Who is the manufacturer? Was it a crate engine or stroker kit? If crate, did they provide the dyno sheet with the engine? Link to comment Share on other sites More sharing options...
parkia86 Posted December 16, 2015 Author Share Posted December 16, 2015 The engine was manufactured by ATK it is their HP25.. no dyno sheet on hand (the mechanic might have it)...my jeep is a 1987 Comanche... from what ive read the renix should adapt to the stroker pretty well... but it just isnt running right..it feels worse than my old 4.0L. I should note that the ECU has been reset... multiple sensors replaced or swapped out with working sensors.. compression and fuel pressure is good.... Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 16, 2015 Share Posted December 16, 2015 Maybe ATK doesn't provide a dyno sheet, or even test run the engines after they build them - I don't know. I went with a Hesco crate engine 12 years ago (it had the dyno sheet) and never had any problems. How did you reset the Renix ECU? And what are the specific symptoms why "it just isnt running right"? Link to comment Share on other sites More sharing options...
parkia86 Posted December 16, 2015 Author Share Posted December 16, 2015 well the mechanic didnt tell me the specifics on how he reset it... i am assuming he connected the battery wires together....the symptoms as he stated were : engine would fire right up but it had very little power... and felt very weak. He didn't provide any other symptoms... they swapped the ecu with one from another jeep and it did the same thing.......... Link to comment Share on other sites More sharing options...
outlaw star Posted December 16, 2015 Share Posted December 16, 2015 well the mechanic didnt tell me the specifics on how he reset it... i am assuming he connected the battery wires together....the symptoms as he stated were : engine would fire right up but it had very little power... and felt very weak. He didn't provide any other symptoms... they swapped the ecu with one from another jeep and it did the same thing..........I'd be looking at timing and checking compression first. Just because they sold you a rebuilt/stroked engine doesn't mean that they 100% know what they're doing. The guys in the club down here have had bad luck with their engines. Link to comment Share on other sites More sharing options...
parkia86 Posted December 16, 2015 Author Share Posted December 16, 2015 The first question I asked him was whether or not he checked compression. He said it all checks out and he doesn't think it's an engine issue. I was paranoid because the engine arrived with the RMS installed backwards. But if every sensor works etc.... I'm nervous the motor is a dud. Link to comment Share on other sites More sharing options...
Strokermjcomanche Posted December 16, 2015 Share Posted December 16, 2015 They installed the RMS backwards? I'm sure they know what they're doing ... Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 16, 2015 Share Posted December 16, 2015 Briefly glancing at ATK's website, they state the following: ATK VEGE tests almost every engine that leaves our factory. ATK VEGE issues a Birth Certificate with each engine that has been tested containing the Serial number, Oil Pressure, Water Temperature, Compression, and Testing Time. ATK VEGE averages 1.7 day delivery time plus FREE SHIPPING to anywhere in the United States. Translated, They test almost every engine to see if it runs. Read no dyno numbers. That's not good enough mate. :shake: Hopefully it will turn out to be something external to the engine and a simple fix for you. Link to comment Share on other sites More sharing options...
parkia86 Posted December 16, 2015 Author Share Posted December 16, 2015 So kind of a silly question... But if the compression is good then the engine itself can be considered to be in good shape? I paid by credit so I can dispute etc... Although I might be out the install cost. They did warrant the RMS fix so it might not come to that but the mechanic is almost at a loss for why it's running like $#!&. Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 16, 2015 Share Posted December 16, 2015 Just curious - did you get the "birth certificate" for your engine? Link to comment Share on other sites More sharing options...
parkia86 Posted December 16, 2015 Author Share Posted December 16, 2015 I had it delivered to the mechanic I will swing by and check tomorrow. Link to comment Share on other sites More sharing options...
MJCARENA Posted December 17, 2015 Share Posted December 17, 2015 Could be that the timing chain was installed off a tooth. Link to comment Share on other sites More sharing options...
parkia86 Posted December 18, 2015 Author Share Posted December 18, 2015 Turns out it is running very very lean. The injectors I bought from Amazon weren't rated to 24 lb/hr and I'm also putting in a hesco adjustable fuel pressure regulator. This should fix the problem! Link to comment Share on other sites More sharing options...
gte636p Posted December 18, 2015 Share Posted December 18, 2015 Put an ATK stroker in my '98 and the timing would not set right. It seems if you use a certain camshaft (which ATK used in mine) you need to rotate the distributor to get the timing set right. I reset the distributor three times by the book and had no power after setting it. If I pushed it the motor would start backfiring, etc. In the end I has to cut one ear off the distributor hold-down and place a fender washer around the hold-down bolt to help hold the distributor in place. It's been about 5 years since then and I have no other issues with anything. YMMV. Link to comment Share on other sites More sharing options...
parkia86 Posted December 18, 2015 Author Share Posted December 18, 2015 Interesting. How in the world did you figure that out? Did you have the same sluggish symptoms as mine? The mechanic seems positive that new higher powered injectors with the regulator will solve the problem. Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 18, 2015 Share Posted December 18, 2015 Put an ATK stroker in my '98 and the timing would not set right. It seems if you use a certain camshaft (which ATK used in mine) you need to rotate the distributor to get the timing set right. I reset the distributor three times by the book and had no power after setting it. If I pushed it the motor would start backfiring, etc. In the end I has to cut one ear off the distributor hold-down and place a fender washer around the hold-down bolt to help hold the distributor in place. It's been about 5 years since then and I have no other issues with anything. YMMV. Did you ever put a timing light on it to see what the actual advance was? I have a Hesco RVOB6 cam in my stroker and it never occurred to me that I might have to advance the timing for it. It does run fine though, but maybe it could run better. I've got a spare CPS I can play with and make it adjustable. Link to comment Share on other sites More sharing options...
theislandnut Posted December 18, 2015 Share Posted December 18, 2015 I set the timing with a vacuum gauge and havn't used a light in years. The highest vacuum your motor will make at it's specified idle is a well tuned motor. I have also had to move the number one wires location on the distributor cap to the next and then rest of them accordingly to get enough rotation of the distributor Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 18, 2015 Share Posted December 18, 2015 Too much room for error doing vacuum timing. I'd rather look at the timing pulses and read the advance on the 4.0 since the marks are there. Link to comment Share on other sites More sharing options...
theislandnut Posted December 18, 2015 Share Posted December 18, 2015 I`m am not sure if I have ever been happy with a by the book tune set to what the manufactures specs are. If the motor came in a crate from jeep themselves I would use a light to get it in the ballpark then likely tune from there. Degrees of timing are average numbers created to make an acceptable tune on a average motor. The specific fuel pressure is the same kind of law of averages. Using a vacuum gauge to tune fuel and spark is old school and takes a bit of practice. But. It tunes that specific motor, with it`s modifications, tolerances and wear. Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 18, 2015 Share Posted December 18, 2015 ^^ I agree with a lot of that. The whole point of tuning is to provide the engine the best air/fuel mixture for optimum performance as close as possible for all driving conditions from idle to WOT and everything in between. The best way to achieve this is by monitoring changes to the A/F readings over these conditions using an A/F meter. The narrow band meters are a good tool for this but the more expensive wide band meters are much better. The tuning method(s) used to achieve the optimum A/F mixture over the power band is not important; it's the end result only that matters. To me an A/F meter is the best tool available for proper engine tuning, not manufacturer's "recommended" specs and values. Link to comment Share on other sites More sharing options...
gte636p Posted December 19, 2015 Share Posted December 19, 2015 I swapped the new motor in and did the injector swap at the same time (I think??) along with the 99+ intake and bigger exhaust. So, honestly I could have cause more problems for myself than I tried to solve. I did have one injector that was stuck open causing some issues for a little bit as well. That said, I hunted for what I mentioned earlier for a while and found one reference to it... if you look at picture #5, this is exactly what mine looked like when thrown back together. If you rotate it to get the tabs to align you get no power at all. I had to cut the tab off and re-install. http://www.cherokeeforum.com/f2/distributor-timing-problem-110907/ Link to comment Share on other sites More sharing options...
HOrnbrod Posted December 19, 2015 Share Posted December 19, 2015 gte636p, the OP still has the Renix system (I think), and you are OBD2 with your 98. For OBD1 and 2 the distributor only controls the cylinder selection and firing of the injectors. It does not change the timing. I think your initial power problems were caused by injector misfiring because your dist didn't line up w/o cutting the alignment for whatever reason. Did you ever try another distributor? Link to comment Share on other sites More sharing options...
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