bobbylx

So a while back I swapped my original 1987 4.0 for a 1996 4.0 complete block. I used the intake/exhaust, dizzy, all accessories from the 87 as well as the sensors.

It was a success and is running and is now my daily driver. But I have a few questions about performance.

It runs fine for the most part but I can tell it's not 100%. The best way to describe it is that it's a bit sluggish on the throttle and the idle tends to go low from time to time. It won't stall out or anything, it just goes from a normal idle to fairly low then back up. I'll give a rundown of what I've done so far.

As I said, I used a 96 complete block with head. I also used the 96 fuel injectors. It was rebuilt 18k miles ago. During the rebuild I completely cleaned the throttle body and ran all new vacuum lines. I put on a new dizzy, wires, and plugs and also replaced all ground cables with 2/4 gauge and my positive battery cable. I did give it a seafoam treatment through the big vacuum line from the brake booster to intake, so I will most likely change the plugs again soon. I also cleaned all electrical connections with cleaner and qtips.

With that said, what other items should I clean/replace that may help improve the overall throttle response and performance of this thing? Again, when driving it runs really well, it just feels a bit sluggish and I have the wonky idle. Could I be missing some vacuum lines? The vacuum lines were a mess when I bought it, but I'm pretty sure I got everything connected again.

I'm also unsure about the fuel mileage on it. I haven't gotten an accurate reading yet, but I've put 130 miles on the new motor and have used between 3/4 and 1/2 a tank of gas. I know it's not going to be great, but it seems a bit low to me.

Just some other tips and things to check would be good. I've been checking Cruisers Renix tips thread and wondering which ones might apply to my situation.


Oh...and a side note. Last night while the engine was running I was looking around and checking out some stuff. While I was checking my plug wire I got my hand close to the coil and got a nice zap!! I've not had that happen before, so is that normal or is that an indicator of a short of some kind??

austinjoe13

EGR? Is the idle pretty rough?

bobbylx

I did take the EGR valve off and clean it, I guess it could be bad. The idle is pretty smooth for the most part other than when it gets low for a minute. If I get a chance I'll step outside on my lunch break and make a video of it.

austinjoe13

Just delete it. Weld it shut or clamp the vacuum line. The solenoid like to go bad also.

bobbylx

http://s1196.photobucket.com/user/bo...b746f.mp4.html


Here is a quick video I took of it in action. From what I can tell the slow start is typical with the renix 4.0, but notice the droopy idle. Does this help the diagnosis any?

freegdr

Timing sounds lazy when reving to me.

fallenknight308

Hard to tell for sure but it sounds like you might have an exhaust leak.

randall L

Throw a vac. tester on there & pay attention to the scenarios listed here......

http://www.secondchancegarage.com/public/186.cfm

cruiser54

Which intake/exhaust gasket did you use? HO or Renix?

Check for vacuum leaks as suggested and check the vacuum with a gauge as suggested.

#12 abd #13 in my Renix Tips will help ensure the dizzy is indexed correctly.

DFlintstone

Also..Does it idle fine for around 20-25 seconds, slow down, (maybe about stall), then rev just a bit, smooth out and repeat?

Separately, you didn't mention that you adjusted the TPS. Also, yea, my secondary wires can zap me. They're not very old.

bobbylx

I used the Renix gaskets. I am almost positive there's a small exhaust leak where it mounts to the head. I know that because I left the top middle exhaust manifold bolt out (can't remember why now, but I know it's out).

I don't have a gauge handy, but I've my my propane torch I'll use to sniff around for leaks.

I did the indexing on it, but that does not mean that I got it spot on. I'll definitely reindex that to try to get the timing perfect.

Oddly enough, you are correct. I didn't pay much attention to it until I got into my parking spot this morning. I sat there and listened to it idle and sure enough, I could count about 25 seconds and then it would slow down and then rev a bit, then back to smooth. Did this happen to you too? What was your solution?

DFlintstone

Well, your third paragraph was a pretty good clew. I think your 02 sensor is toast. Here's a rambling link, with a link. You might check it's heater wire/relay, it's ground, and the wiring there in general before you change it.

Right away I'd heat up faster, Idle smoothed out, and mileage went up when I changed mine. >> https://www.cherokeeforum.com/f2/ren...ce-rms-133153/

DFlintstone

Vacuum leaks suck. I go around with short little shots of starting fluid, if you hit one the sound of the engine will change. Small little shots! You don't want that stuff to accumulate. It's a fire hazard, but It evaporates right away. Also with a tube, or a section of hose you can listen for it. Don't forget the lower O rings on the injectors need to seal as well. (uppers would leak fuel).
The manifold bolts have a habit of loosening, especially that rear one. On anything like that you never want to tighten only one. It can warp/bend, even crack things. If I found that any that where easy to reach where loose, I'd pull the air cleaner and tighten them all, starting in the middle and working out towards the ends. I go over about three times. It's a bear of a spot to get a torque wrench on them all. Just don't ape on it. If its firm and not turning, no point in going on to break it, a REAL *****. The rearmost bolt underneath takes a little doing, but it can be done with the right extension. For that very back one by the firewall I use way long extensions (18"), with a swivel at the socket. Anyway, that's a good thing to check on any old Jeep. ALSO, there is a large line coming off the intake, rear of the TB that goes back to the firewall, across, then forward down to the vacuum ball behind your right front bumper. You can pinch that off or unplug it and cap the nipple to test if you have a leak there.

Jakers

I'm having the the EXACT same issues... I replaced all vacuum lines, TPS, IAC, adjusted TPS, cleaned throttle body and adjusted butterfly. Runs a little better now but it still is a bit rough. Starts up fine for about 30 secs, then idle drops real low, almosts stalls, then jumps right back up again. No issues on highway but in town if I come to a light/stop sign or do a real slow turn then the RPMs start to drop... I was curious if it was my EGR or sensors but I havent down my ground refreshing yet. (Cables/terminals should be in 2morrow) so if new grounds don't fix it then I guess I'm gonna have to check out the EGR/Sensors...

Please keep me posted on your progress as it sounds like I'm in the same boat. The beast is driveable as is but I would like it to run how it should!

DFlintstone

Crusier had been pestering me for a year to clean my dipstick ground. Besides picking up 1/10 of an ohm (.9 to .8), there, that was all that changed besides the 02 sensor. Heat/defrost worked faster, mileage went up, idle is even.

Now with the Volvo/Bosch 280 155 746 injectors, (that's for Renix), and the restriction gone between the air box and the TB, I'm getten over 16, on small roads and gravel! Looken forward to an opportunity to get a "normal" highway figure.

(I'd hit 11 with 703's, and the 02 dead) I'm past 273,000 miles.