Zebvance Posted May 5, 2016 Share Posted May 5, 2016 This has been prominent in my comanche as far as I can remember. It was really noticeable to me when I got my exhaust done (because it was louder). The truck has gotten maybe 5-6k on it for in the past 3 years since the exhaust was put on. When I'm decelerating/ foot off the gas and coming from highway speeds the truck will make several short pulsating revs until I come to a stop. Its hard to explain, so sorry if its difficult to understand. They are all spaced and timed identical maybe every 4-6 seconds or so. The increase in rpms is not a lot. I have a digital tack and it happens almost to quickly for it to register it. But it jumps the rpms about 100-200. The pulses last for about a 1/2 second. Any ideas? Its not effecting the drive-ability that I can tell its just something I noticed that was kind of odd. I do know that it is running super rich. I always have black sut all over my rear truss and very strong smell. I have replaced the IAC (has not been dialed in yet) o2 sensor was done with the exhaust, and new map sensor. I have been getting about 9-10mpg city and 13-14 hwy. Any Ideas 1988 4.0 auto 4x4 pacesetter header to 2.5" exhaust high flow cat magnaflow muffler dumping right after the cab Link to comment Share on other sites More sharing options...
fiatslug87 Posted May 5, 2016 Share Posted May 5, 2016 Leaking injectors, TPS not adjusted? Read the deceleration portion in this thread http://comancheclub.com/topic/50324-open-vs-closed-loop/ Link to comment Share on other sites More sharing options...
Zebvance Posted May 5, 2016 Author Share Posted May 5, 2016 Reading that thread is what made me finally post about this issue in the first place. Injectors are new upgraded 4 hole injectors. Done about 4000 miles ago probably. Should have mentioned that I guess. Link to comment Share on other sites More sharing options...
Zebvance Posted May 5, 2016 Author Share Posted May 5, 2016 I do need to adjust the tps. It is also new. Less than 15 miles on it. The old one was sticking full rev on start up some time. But this issue acts the exact same as when the old one was in. I would "like" to assume that's not the culprit. Link to comment Share on other sites More sharing options...
Zebvance Posted May 6, 2016 Author Share Posted May 6, 2016 Friday morning bump Link to comment Share on other sites More sharing options...
gogmorgo Posted May 6, 2016 Share Posted May 6, 2016 My first thought is it's downshifting. Could also be a thing with torque converter lockup. As to it running rich, a vacuum leak could do that to you, especially if it's causing inaccurate MAP readings. Link to comment Share on other sites More sharing options...
Zebvance Posted May 6, 2016 Author Share Posted May 6, 2016 My first thought is it's downshifting. Could also be a thing with torque converter lockup. As to it running rich, a vacuum leak could do that to you, especially if it's causing inaccurate MAP readings. Its defiantly not down shifting. Its very prominent when it down shifts. Its something in addition. I wouldn't out it past a vacuum leak. I have a new vacuum harness on it and am pretty sure everything it good on it but there are a few lines that the PO has capped. I was almost positive they were to the climate control though since that orvis bottle (or whatever you call it) is not were to be found on my truck and the vents won't change from being stuck in defroster mode. Link to comment Share on other sites More sharing options...
cruiser54 Posted May 6, 2016 Share Posted May 6, 2016 I have the same thing on my 90. I haven't figured out what it is. Have you tried opening the air bleed on the throttle body a bit? Link to comment Share on other sites More sharing options...
Zebvance Posted May 6, 2016 Author Share Posted May 6, 2016 I have the same thing on my 90. I haven't figured out what it is. Have you tried opening the air bleed on the throttle body a bit? No, Ill try that. The truck still doesn't have the steering finished up yet so Its hard to tell of anything I do will work right now since I can't drive it. Link to comment Share on other sites More sharing options...
Zebvance Posted May 8, 2016 Author Share Posted May 8, 2016 Sunday bump Link to comment Share on other sites More sharing options...
cruiser54 Posted May 9, 2016 Share Posted May 9, 2016 Sunday bump I'll try a version of a factory bulletin to see what it does. I have the tester and the IAC exerciser. Link to comment Share on other sites More sharing options...
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