4.0 Tuning exercise: phase 1

[mmag1982]

Hello all,

I finally started tuning my 2001 XJ 4.0. I bought this car 6 months ago with only 30,000 miles on the clock. been parked most of its life.

Since I am a mechanical engineer and a petrol head, I always wanted to tune a car myself.

For the 1st few weeks it ran HORRIBLY. Slow, rough, pinging everywhere in the RPM and went from 0-60 in 12 seconds although its a manual!!

I posted lots and lots of threads in many forums and many people kept telling me its a slow old jeep that wont go any faster. I was not convinced and refused to give up.

So here is what I did:

1. Basic maintenance: filters, plugs, oils, all operating fluids were changed, injectors were cleaned with prestone injector cleaner.


2. after basic maintenance the picture was a bit more clear. The roughness and slowness were actually PINGING everywhere in the RPM range. Full throttle actually made the car slow down!...as if it was choking. No error codes.

3. Tested fuel pressure, 48psi at idle and 45psi at WOT . falls of slightly in extended WOT like 3rd gear runs for example.
Checked vacum lines, no major leaks. I decided to change the VALVE cover gasket and the 2 rubber grommets and the plastic fittings feeding the crank ventilation system, and seal the new ones with thermal RTV. >> Result: pinging was reduced by around 60% and MUCH MUCH more torque was avaialabe.

4. SEAFOAM through the intake vacum, 1/3 of a can very slowly fed into the intake.> no intense smoke as usually mentioned > Result: Idle is more smooth, throttle response sharper, pinging decreased.


4. Brola Turbo XL universal straight through muffler and random technologies universal high flow cat.
I selected those items with the same diameter tubing as the stock items, cut the old flanges and welded them to the new ones. Kept both oxygen sensors as is.
result>> dramatic difference. all I can say is WOW WOW WOW. I didn't ever think an inline 6 can sound like a full blown v8. The jeep pulls much smoother throughout the rev range, very torquey, only slight full throttle ping remains. I have to have something to monitor the Air/Fuel ratio so I know what I'm doing.

5. AEM digital air/fuel ratio meter. > beautiful item, very high quality illumination and fabrication. I installed the sensor in the S pipe about 3 inches away from stock o2 sensor 1. Looking at the guage, It makes sense now.
Idle is rock solid 14.5/14.7, part throttle stays in the 14s.
When the throttle is floored, I momentarily run at 12 or even 11.5 but then it jumps back to 14.5, which is very lean. It behaves as if it cannot maintain a rich afr for a long period of time. For example if I'm doing a WOT run through the 1st 3 gears, 1st gear ends with around 12, 2nd gear things start to drop into 13,14, 3rd all the way 14+.The engine is supposed to be in open loop at WOT, so oxygen sensor inputs are ignored then. This points to either the fuel pump or the injectors.

I purchased these items as well and I'm planning to install them one by one to monitor the effect separately.

- AEM brute force intake with dry flow K&N developed Dry flow filter

- flow daddy header from rusty's

- Hesco 24lb/hr injectors

- Bosch OEM replacement fuel pump.

What I expect is that the intake and the header will push the engine more into the lean side, which is completely not acceptable . I hope I can counter-effect that with the new fuel module and 24lb injectors. Theoretically I should be fine until WOT where the oxygen sensors will be ignored, the injectors migh cause me to run over rich then.

I will update soon with pics and progress. Please let me know what you think and your experiences.

 

[Original_MudButt]

You reduced pinging by 60% and gained torque by replacing the valve cover gasket?

I've never heard of this. Could you explain why this happens?

 

[ColoradoRaptor]

You reduced pinging by 60% and gained torque by replacing the valve cover gasket?

I've never heard of this. Could you explain why this happens?

You need to go check yourself as you cannot read nor comprehend jack ........ :banghead:

 

[DeftwillP]

*pcv valves*

This thread might get more feedback/response in the street performance forum.

Oh yeah, the "flow daddy" is a rebadged marked up APN IIRC. Still a good unit; I have one.

Sent from tapatalk on iJunk
*signature not meant for eyes

 

[tragiccomic1972]

this is very useful... keep us informed

 

[matus2]

Yeah the little bottle fuel injector cleaners do not do much to clean. I would have suggested getting them cleaned professionally and flow tested but you already got new hesco ones. I did read recently in one of the off road magazines here (sorry can't remember which one - maybe someone else can chime in) that increased fuel injector size will not do anything. The computer will just fire the injectors a shorter time to make sure the same amount of fuel is injected as the stock. They did list a way to fool the system to utilize the upgraded injectors. I'll see if I can find the article for ya.

 

[Talyn]

5. AEM digital air/fuel ratio meter. > beautiful item, very high quality illumination and fabrication. I installed the sensor in the S pipe about 3 inches away from stock o2 sensor 1. Looking at the guage, It makes sense now.
Idle is rock solid 14.5/14.7, part throttle stays in the 14s.
When the throttle is floored, I momentarily run at 12 or even 11.5 but then it jumps back to 14.5, which is very lean.

As you found out that is where your problem lies. Have you check the MAP and TPS sensors? The MAP is the most important item during WOT. Your fuel pressure falling to 45psi @ WOT shouldn't be enough of an issue to cause it to go that lean.

 

[mmag1982]

as for why replacing the valve cover gasket reduced pinging , my interpretation is that since it was leaking oil it was also acting as a major vacum leak. The valve cover is under -ve manifold pressure from the 2 rubber hoses going into the plastic T fittings, by sealing it I think I just eliminated a vacum leak which was making the engine somehow run more lean than it is already, hence pinging reduced.

@ matus2, I agree: but the catch here is that at WOT the ECU should go into open loop mode which is basically ignoring the o2 sensors and feeding the injectors from preset parameters. I am relying on this simple fact to enrich the engine, hence increase power with added air flow from intake, throttle body, etc..My AFR gauge so far confirms that this is happening, however I need to sortout my fuel pump 1st to have a conclusive result.

will keep you posted

 

[Dr. Dyno]

but the catch here is that at WOT the ECU should go into open loop mode which is basically ignoring the O2 sensors and feeding the injectors from preset parameters.

The '00-'01 4.0 engines stay at a 14.7:1 AFR under WOT up to 2300rpm before they go richer.

 

[Original_MudButt]

You need to go check yourself as you cannot read nor comprehend jack ........ :banghead:

1. PHU QUE.....

2.

...I decided to change the VALVE cover gasket and the 2 rubber grommets and the plastic fittings feeding the crank ventilation system, and seal the new ones with thermal RTV. >> Result: pinging was reduced by around 60% and MUCH MUCH more torque was avaialabe.

Just what exactly was I supposed to comprehend in that statement? That replacing the valve cover gasket gives you gobs more torque?

I don't see how that's possible so I simply asked if he could explain it to me. You know since I'm obviously an idiot, I was hoping someone could teach me about mechanical stuff.........

 

[Talyn]

The '00-'01 4.0 engines stay at a 14.7:1 AFR under WOT up to 2300rpm before they go richer.

He is saying that it goes richer, then goes back to 14.5:1 or so, which it shouldn't be doing.

 

[mmag1982]

hey everyone,

- The new fuel module is in, I can notice no change in performance but something interesting is happening in the Air/Fuel Ratio meter. The car stays in between 15 to 14.6 nearly all the time, until around 3000rpm where is starts to gradually drop in the 13s.

Full throttle is now a different story, as dr. Dino said, above 2500 RPM it DUMPS fuel, the gauge showing 12 and drops to around 10.5 or 11 at 5000RPM.

Clearly the stock fuel system is more than capable of delivering, the problem now is that the slight pinging moved from WOT to partial throttle.

- there seems to be a point in the throttle at around 85% opening where I can feel I get much better acceleration, that point happens to be 13 to 13.5 on the AFR. Unfortunately I can't hold it on this point for long. If I floor it I still get that choking feeling at AFR 11s and 12s. Have no explanation yet for that.

- AEM intake installed, or actually partially installed. The heat sheald that came with it is a complete joke. Its made of metal, which means it will actually absorb heat rather than shield it. plus it didnt fit..holes didnt align and the hood didn't close!!!. I ensed up intalling the intake tube with the filter on its own. Result]] much sharper throttle response, the throttle pedal feels much more accurate and big improvement above 3000rpm. The engine actually can now easily rev to 5000RPM without feeling like its going to explode.

- Some how the engine bay doesnt feel as hot as it used to, I can now actually touch the hood after a long drive, maybe its the free flowing exhaust?

- big improvement in MPG, for the same drive to work I am getting around 20% more range. will try to quantify it update, but I'm sure there's an improvement.


- 0-60 tested : 9.6 sec vs. 12 when I first bought it,guess i am on the right track somehow

Next. The flowdaddy header

 

[techno1154]

Good info,...Really good info, especially regarding the pinging and the AFR.

My XJ have quite a bit of hesitation at RPM's above 4,000 +/-. I think it may be caused by the 19# injectors in it and a questionable MAP sensor. Some thing to look at next time I get my hands on it.

 

[Dr. Dyno]

- The new fuel module is in, I can notice no change in performance but something interesting is happening in the Air/Fuel Ratio meter. The car stays in between 15 to 14.6 nearly all the time, until around 3000rpm where is starts to gradually drop in the 13s.

Full throttle is now a different story, as dr. Dino said, above 2500 RPM it DUMPS fuel, the gauge showing 12 and drops to around 10.5 or 11 at 5000RPM.

It sounds like your engine's now behaving normally. Those AFRs are typical of the quirky tune that DC decided to program into the Jeep's computer.
When I had my old 4.0, the last mod I did after all the external bolt-ons (before I was infected with strokeritis) was to port the head, and that really made the engine rip between 3000rpm and the 5200rpm rev limiter.

 

[mmag1982]

@ Dr. Dyno,

I still think something is not running at 100% in my engine. And I think its something basic. here are my reasons why, please tell me what you think

- for some reason I still feel a 0-60 of 9.6 for a manual 4.0 is still too slow. I am not picking on tenth of a second here, but just a feeling. I think I should be in the 8's specially with the mods I have on now.

- Contrary to popular belief, I know this wont make sense, the engine has very poor torque below 3000rpm!!!, Actually there is an obvious " bump" in the power curve as it suddenly wakes up beyond 3000 rpm. The reason is simply beyond me.

- There is a slight shudder and clonking noise as the engine is shut off, as if a rotating loose part is slowing down as the engine is shut off.

Something is still not right.

What do you guys think as a list of items to check that can affect power output in a well maintained 30,000 mile 4.0? My engine is very sound mechanically , no overheating, all basic maintenance done..etc,

From what I done so far I eliminated any issues with the fuel system, air intake system and exhaust system ( except for the possibility of a minor crack in the stock header )

 

[RedChuck]

mine has that noticeable bump in power around 3000rpm.

 

[Dr. Dyno]

Contrary to popular belief, I know this wont make sense, the engine has very poor torque below 3000rpm!!!, Actually there is an obvious " bump" in the power curve as it suddenly wakes up beyond 3000 rpm. The reason is simply beyond me.

I think you nailed the reason why the engine comes alive at 3000rpm when you said:

I can notice no change in performance but something interesting is happening in the Air/Fuel Ratio meter. The car stays in between 15 to 14.6 nearly all the time, until around 3000rpm where is starts to gradually drop in the 13s.

To answer your other question.

- There is a slight shudder and clonking noise as the engine is shut off, as if a rotating loose part is slowing down as the engine is shut off.

Something is still not right.

What do you guys think as a list of items to check that can affect power output in a well maintained 30,000 mile 4.0? My engine is very sound mechanically , no overheating, all basic maintenance done..etc,

You could start by doing a compression check on all cylinders to rule that out as a cause of power loss.
The clonking is hard to diagnose and this is a long shot, but I've seen a couple of cases posted in the forums where the piston skirt has broken off on later model 4.0 engines. If the noise really does concern you, it might be a good idea to pull off the oil pan and inspect all the bottom end components.

 

[Talyn]

Also, check your flex plate bolts.

 

[gradon]

With light loads and low throttle input the pcm is in Closed Loop mode and targets 14.7:1afr. Once you get past 3Krpm, it goes to Open Loop mode and should dip into the high 12s with high throttle input.

 

[badron]

With light loads and low throttle input the pcm is in Closed Loop mode and targets 14.7:1afr. Once you get past 3Krpm, it goes to Open Loop mode and should dip into the high 12s with high throttle input.

How's this for a fly in your stuff. Is the reason for the HP bump above 3K (((JUST))) do to the ECU going open?
Maybe it's that funny looking intake and the reworked cam that came with it. Lets see according my calculation they should kick in at about.............3k wow................... REALLY it's 2.5 K
Why not let it go rich sooner?
Well the factory boys got to think about smog numbers, MPG and other thing as well.
As for MPG (city) testing. Forcing the ECU to stay in closed loop during the mild acceleration below 3k regardless of what the MAP wants. Should help keep numbers up.
MPG highway testing is done at a ((STEADY))) speed of only 45 MPH. This steady speed will keep the vacuum up and the MAP will stay out of the way.
Smog testing. Also most of this testing is done well below 3k. Yes some WOT testing is done. Some one want to look up to what RPM this testing is done. I forgot.
So the factory gets it's smog numbers and MPG number below 3K and all the fun stuff can happen above 3K. Factory boys don't look so stupid any more do they.
Besides how much go fasting do you do below 3k?