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5.9 in a Wrangler, feels like I'm dragging a trailer around

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5.9 in a Wrangler, feels like I'm dragging a trailer around

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Old 07-07-2018, 09:11 PM
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Default 5.9 in a Wrangler, feels like I'm dragging a trailer around

Hey all, incoming wall of text.

I feel like I've been reading DodgeForum threads in my sleep for the last few months trying to figure out a nagging low power problem on a 5.9 Magnum that I swapped into a Jeep TJ.

Where to begin... well, I swapped the drivetrain from a '99 Ram 1500 into my '99 Jeep Wrangler over the winter. It's running well, sounds good, idles smooth, shifts through all the gears, etc, but it just doesn't have the power I feel like it should. It's on 35" tires with 4.88 gears, and literally won't spin the tires in dirt. Drops out of overdrive on any minor hill on the highway. I have a '97 Grand Cherokee with a 5.2 that will blow the doors off it, with stock 3.73 gears on 31's. It seems to be missing power at all RPM ranges, not just low end or high end, so I feel like I'm looking for a systemic problem. It SOUNDS fine when accelerating hard. No pinging or missing or stumbling, it just doesn't GO like it should. Like I'm dragging a trailer around.

Starting at the beginning:
The donor truck had about 200k on it, ran okay but the trans was slipping and had burnt fluid in it. I yanked the drivetrain, stripped the motor to see if if needed a rebuild, and found crosshatching still on the cylinders, so I went with a re-ring kit. Cleaned all the carbon off the pistons and ran a ball hone through the cylinders, changed out main and rod bearings and put her back together. Cam bearings were smoked so I changed those too. Heads were cracked of course, and I replaced them with THESE HEADS. Put the engine back together with the stock cam, new timing set, new lifters, original pushrods and rockers. The engine got a new oil pump, new distributor, new cam, new coil, new crank, water temp, oil pressure, O2, and MAP sensors as well as plugs and wires, etc. I did not change the IAT, TPS, or IAC. I put THESE BLOCKHUGGER HEADERS on to fit my application so the engine would fit in the Jeep's engine compartment.

I rebuilt the 46RE trans, replaced both bands and all clutch packs (frictions and steels) and installed a TransGo shift kit. It got hot on me after a long trip down the highway about a month ago, hot enough to go into limp mode, so I changed out the fluid and filter and added an auxiliary cooler and a temp gauge. So far so good. There was a little more metal than I was expecting in the trans after 500 miles, but I didn't change the torque converter (idiot) when I did the rebuild so I'm guessing it was leftover crap from the old fluid, because there were no signs of excessive wear in the trans when I pulled the pan and valve body and looked over the clutch packs and bands again. Shifts fine, has all 4 gears plus TCC lockup working properly.

I built the wiring harness myself using the factory service manuals for both vehicles, obviously using the PCM from the '99 Dodge. The evap system is hooked up and working properly. There are no check engine lights. Since they are both Chrysler products with a CCD bus, the Jeep gauges work correctly and show all the same values that I read on a scan tool. The custom exhaust that I had made includes a catalytic converter and both O2 sensors installed. I performed the distributor fuel injector sync with a scan tool since I had changed the distributor.

As I said, it's in a Jeep TJ Wrangler on 35" tires with 4.88:1 gears. The same ratio I was running with the 4.0 inline 6 that I removed. It feels normal when cruising around town off-idle, but when you get hard on the throttle, there just isn't much there. If anything, it has the same or a little less power than the 200,000 mile 4.0 liter with a manual trans that I pulled out of it. It cannot climb a moderate hill on the interstate without dropping into 3rd gear, and with 4.88s it's turning about 2300 rpm at 70, so it should have plenty of torque to stay in O/D. The vehicle is a street legal 4-wheeling/rock crawling rig, and there have been a few instances where I've been pushed up against a rock in 4-low and floored the accelerator and it just sits there and bogs, where I was expecting wheelspin. The only "real" symptom I can come up with is that, under hard throttle applications, I get a very slight sulfurous / catalytic converter smell, but I put a backpressure gauge in the front O2 sensor bung and there is 0psi of backpressure, so the brand new cat is not plugged, even though that seems to match some of the symptoms.

I feel like the cooling system pressurizes a little more quickly than expected when the engine is started, but there are no bubbles and no signs (smell) of combustion products or oil in the cooling system, or coolant in the oil to indicate a head gasket or water jacket problem. It does jump to 20psi within a few minutes of the engine idling. Even if this was an issue, I wouldn't expect it to cause this significant of a power loss. This motor is meant to drag around a 8000 lbs one-ton truck, it should RIP in a little Wrangler.

Next we come to what I have already checked.
No excessive backpressure upstream of catalytic converter.
All cylinders are at 145-155 psi compression.
Fuel pressure is 49 psi with engine running. Drops when engine is shut down, but that is a fuel pump check valve, not injector bleed down.
Plenum gasket was replaced during rebuild, no oil present in manifold.
Vacuum on analog gauge is approximately 20inHg, vacuum gauge readings match MAP sensor readings. Steady needle, drops on heavy throttle and comes back to steady 20in.
Verified spark plug wiring firing order multiple times. All spark plugs are showing good brown color on removal.
Verified cam timing, removed valve cover and rotated no 1 cylinder past timing mark TDC on exh/intake stroke crossover and watched valves. Intake/exhaust cam overlap happens right at timing mark.
Verified injector spray. Removed fuel rail, pressurized rail and put 12v to each injector, all had good strong stream of fuel
Verified that throttle opens fully on full pedal application.
No audible vacuum leaks or idle problems.
Checked all sensor readings on scan tool against actual readings. TPS values normal, coolant temp and IAT very close to infrared thermometer readings of intake, MAP matches vacuum gauge readings, etc.
Watched datastream while driving, nothing jumped out at me. O2 sensor correctly going into closed-loop during normal operation. Short term fuel trim swaps from negative single digit % to positive single digit. Long term fuel trim stays between -6 and -10%.

I keep FEELING like it's gonna be something completely silly, like mis-timed plug wires or the cam timing being a tooth off, but it just purrs too nice for that and I've checked both of those.
My next things I can think of to check are:
Leave fuel pressure gauge on while driving to verify that the Jeep fuel pump isn't having trouble keeping up.
Remove valve covers to make sure all rockers are moving and cam isn't flat/rocker bolts haven't backed out.
Check headers to make sure they fit correctly and aren't blocking off part of the exhaust ports.

If anyone has anything else they can think of, I'm ALL ears. A tech I know asked me about the coolant temp sensor because that would affect all RPM ranges, but it's reading normally. Also, the fact that it's a problem ALL THE TIME across ALL engine loads, (even when the PCM is in open-loop mode and ignoring sensors) and the air/fuel ratios seem okay make me FEEL like it's an airflow problem of some kind. I'd also believe a programming issue, since theoretically a really conservative tune would probably feel like this too. It's an engine swap so anything is on the table, no matter how weird. Whatever you've got. HELP before I get so frustrated I rip this bad boy out and put the six cylinder back in it! Thanks!



 
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Old 07-08-2018, 02:32 PM
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Very thorough. Thank You.

I think the idea of running it with the fuel pressure gauge attached is a good plan, though, if that were a problem, I would expect to see fuel trims spike under load.

Did you spec out the cam while you had it out? They really don't fail very often on these motors.... but, ya never know.

Did you ever drive the truck the motor/trans came out of? Or did the blown trans prevent that? Would be curious how it ran in its original home.

Check he part number on the pcm. See if it has an "authorized software update" sticker on it. If it does, that would be the "death flash"...... but, I still don't think that would account for your severe lack of power. If you had a dead cylinder or two, you would KNOW that just as soon as the trans hit O/D. It would feel like the Jeep was trying to shake itself apart.

Can you do data logging? Would be interesting to see what the numbers look like, in both normal cruise, and hard acceleration.
 
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Old 07-08-2018, 03:08 PM
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Did you set the fuel sync?
 
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Old 07-09-2018, 12:12 AM
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Do you have a way to watch the timing advance/retard?
 
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Old 07-09-2018, 07:15 AM
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I just have a consumer obd reader at the moment, but I can borrow a professional grade scan tool at work and do some logging. I can read timing from the PCM but it only updates maybe once every two seconds, so I need the better tool.

Unfortunately I did not get to drive the donor truck to know if it was already a dog. It had no brakes, I picked it up cheap, and I only drove it out the driveway and onto the tow truck.

I visually inspected the cam on all the bearing surfaces. Since the cam bearings were bad, I expected the cam to be too, but it was clean. I looked at all the cam lobes but I can't say for sure i wouldn't have missed something minor. I did notice this weekend when I started it I had a slight lifter tap when cold, which I wouldn't expect with new lifters, so I'm going to investigate the valvetrain further tonight after work.

Thanks for the responses.
 
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Old 07-09-2018, 10:48 AM
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If all other routes trouble shooting fail, just a thought here, maybe put the jeep on a dyno and see what your getting. if the numbers come back where they should be you are just expecting to much from the 5.9. I love my ram (01' with 5.9/46re, 4.56's and 37's) but its a dog. Id expect 160-180 at the rear tires max from a 200,000 mile engine. What were the factory number, somewhere around 265-275 hp at the crank? With parasitic loss of a 4x4 that would put you down to 200hp on a fresh motor.
 
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Old 07-09-2018, 11:12 AM
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Originally Posted by jlake4130 View Post
If all other routes trouble shooting fail, just a thought here, maybe put the jeep on a dyno and see what your getting. if the numbers come back where they should be you are just expecting to much from the 5.9. I love my ram (01' with 5.9/46re, 4.56's and 37's) but its a dog. Id expect 160-180 at the rear tires max from a 200,000 mile engine. What were the factory number, somewhere around 265-275 hp at the crank? With parasitic loss of a 4x4 that would put you down to 200hp on a fresh motor.
I have indeed thought of that, but my experience with my heavier 5.2 liter ZJ that also has a higher effective gear ratio tells me that it should have a bit more oomph down low and I'm probably missing something. 4.88 and 35s is a lower than stock ratio, the compression numbers are ok, and the heads are new.

I've considered putting a hughes cam, intake, TB, and a tuner on it to get some more love, but if I have an underlying issue I can't resolve that isn't related to one of those, it would be a huge waste of money that I'd obviously like to avoid.
 
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Old 07-09-2018, 11:20 AM
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Originally Posted by HeyYou View Post
Very thorough. Thank You.

I think the idea of running it with the fuel pressure gauge attached is a good plan, though, if that were a problem, I would expect to see fuel trims spike under load.

Did you spec out the cam while you had it out? They really don't fail very often on these motors.... but, ya never know.

Did you ever drive the truck the motor/trans came out of? Or did the blown trans prevent that? Would be curious how it ran in its original home.

Check he part number on the pcm. See if it has an "authorized software update" sticker on it. If it does, that would be the "death flash"...... but, I still don't think that would account for your severe lack of power. If you had a dead cylinder or two, you would KNOW that just as soon as the trans hit O/D. It would feel like the Jeep was trying to shake itself apart.

Can you do data logging? Would be interesting to see what the numbers look like, in both normal cruise, and hard acceleration.
The PCM does not have the software update sticker, but it does say "remanufactured". Hmmmm.... now I wonder if it's the right computer... any way to identify based on this decal?



Sorry, I don't know how to resize it from my phone..
 
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Old 07-09-2018, 12:29 PM
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I had time to log a couple full-throttle takeoffs on my coffee break using the obd software on my phone. It will only let me log 4 data streams at once, so the graphs are slightly different. Looks like fuel trims level off during heavy loading, expected because the PCM runs off tables at full throttle, correct?
Only thing that jumps out at me is timing. Seems to be retarded pretty significantly from what I expected. I assume this is for knock prevention? Is this the death flash I've seen so much about?




To be honest, it actually felt sort of okay other than the first 50 feet or so. These were basically 0-60 full throttle.
 
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Old 07-09-2018, 02:30 PM
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Got a couple more graphs on my lunch break.
Getting on the highway and up to 65:


and 35-45 mph cruising on side road. You can see a little spike in throttle position when I hit a little hill, and resulting drop in timing advance. Normal?

 
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