Ported 4.0L, MPG and such stuff

[Rapoza]

Hello guys,

I'm going alone into a big diagnose of my engine and I gess some of you can give any advice or ideas on the point.

I ported the head of my XJ 4.0L 91's while I was repairing the engine, as I bought the Jeep in a really bad shape. I followed the directions on the Dino's excellent page and changed bearings, rings and water pump. The new head (0331) was ported and milled 0.254mm (0.010") to increase compression in a attempt to contain the gas mileage and making a more efficient powerplant. The throttle body was also bored and I replaced the bad TPS with a spare one from my 2.5L YJ.
Spark plugs where also replaced with a used good ones, as the olds where all wrecked.

The result wasn't expected by me. It has a very stable iddle.
The smoke on tail pipe is clear an no smelling (perhaps a little burnt firecracker smell)
The power is biiiig and comes from the very bottom as it revs 'til 5500
But it has a very poor mileage of 20L/100Km (11,8 mpg) that worries me more than a lack of power.
It also overheats the exhaust pipe a nice bit. Figure, that in the last trail I wasn't able to see through the white smoke column that was coming from the eng compartment after I ran out of a little water splash.
The cat converter also heats very well so it smokes from its case only by cruising on the road.

I was starting to buy all new sensors around, but before wanna know what you guys think about.

Gettings,
Sergio Rius Rodriguez
http://saposysalamandras.dyndns.org

 

[87manche]

an overly rich condition will cause the cat to heat up. I would say that's a likely place to start. I'd try the O2 sensor first. Make sure that it's heating up enough to go into close loop mode.

 

[Dr. Dyno]

Yeah, a bad O2 sensor does sound like the most likely diagnosis.

 

[Rapoza]

My XJ has metric dials. So the temp needle moves very little around the 100 degrees mark (212F), that is in the middle. It raises less than 4mm (half to next mark) when in heavy load and lowes much more when coming down a large hill.
It takes about 2 minutes to get warm from a 10 degrees ambient temperature. It's the car that warms up so faster than any I ever owned before.

I changed new the thermostat, computer heat sensor, water pump, 3 row radiator, the big hoses... and relocated the gauge sensor to thermostat housing in the path of the heather output (the front round inlay)

I multimeter tested the output of the O2 and obtained a 4.5V signal and after little a varing 0,xx one. So I assumed it was functioning properly and the stuff was hot. Also it had the 12v input signal. I tested it near the sensor and also close to ECU.

Can the O2 still be bad?
There's any (measuring or such) test to know exactly if my ECU is in closed loop mode?

Ah, it also cranks for about 5 seconds before starting whenever the engine temp is (and battery, I tested regular, gel and starter ones). Sometimes he starts earlier than that but always after a big *burp*

 

[87manche]

sounds like it's heating up properly then.
do you mean .45 volts?
.45 volts is the proper voltage of stoich. It should bounce around there after it's warmed up and in closed loop mode.
As the voltage goes up the ECU will richen the mixture, so if it is reading high then the ECU will be running too rich. Honestly I'd replace the O2 sensor before spending big cash on the others and see what happens. Seeing the cat glowing red hot points me to a too rich condition, or a cat that's hosed.

 

[Rapoza]

Yes 87manche, I was meaning 0,45v. I can tell you that when hot it moves around 0,8v so it would be rich then.
The O2 for me is the most expensive sensor (about 130$). I must try to find an aftermarket if it exists.

What do you mean with a hosed cat?
A cat that is clogged and exhaust vapours cant go through him? or a cat that has been emptied inside and crossed with a pipe in order to "gain" anything?

I suspected on a clogged cat, as we have here lots of mud and very dirty owners. And also I was thinking to empty the cat inside as I will still have the wranglers one for emissions tests.
That will be worse than good?
Time ago I had a sports car that I had removed the cat and I didn't notice any adverse effects (very little gain to none though).
A stock cat here can be 1000$-1500$.

Thanks for helping me. And sorry for extending me in excess. I like to explain me alot :shhh:
Sergio Rius Rodriguez
http://saposysalamandras.dyndns.org

 

[WVridgerunner]

Hey Man,
Can you get a cat from Jeg's or Summit parts. They have replacement cats for a high performance set-up and they run around $150.00, and they reduce
back pressure and increase flow.
www.Jegs.com
Replace the O2 senser with a resister the value you need for the correct running value and keep trucking.
Hope all is fine for you in the future.

 

[Rapoza]

Sorry man, but I'm not in USA.
:shocked: What you said 'bout a resistor?? And how is supposed the ECU to know when my engine needs to eat some more?? :huh:

In that case my ECU will always be throwing a O2 signal stuck in the middle and indded the idiot light always on.

The easy deal on exhaust I found just a few minutes ago where pacesetter headers at 550$ more or less.
I already repaired the cracked stock headers and straighten the bent main pipe so this change was in the tasklist. Will this brand-model (XJ) be good for good torque at lows?

 

[87manche]

Sorry for the slang. By hosed I ment malfunctioning. It may be worth taking it off temporarily to troubleshoot it. Won't cost anything.

 

[Dr. Dyno]

Yes 87manche, I was meaning 0,45v. I can tell you that when hot it moves around 0,8v so it would be rich then.

A reading of 0.8v indicates that your O2 sensor is functioning normally. For the O2 sensor to cause the engine to run rich, it would have to falsely send out a very low voltage signal (0.0-0.1v) that the PCM would interpret as a lean condition. The PCM doesn't know that the O2 sensor is giving wrong information so it goes ahead and richens the A/F mixture.
The cause of the problem lies elsewhere. Possibilities include:

1. Clogged cat (you can hollow it out).
2. TPS. You used the one from a 2.5; perhaps the signal is different.
3. Bad manifold air temp. sensor.
4. Bad coolant temp. sensor (the one in the thermostat housing).
5. Vacuum leak. Check all the vacuum lines coming off the intake manifold, especially the one to the MAP sensor.

The MAP sensor itself should be OK. A bad MAP would cause very poor engine running and difficult starting (sometimes no start).

 

[Rapoza]

Uhmmm, so I will do as follows:

I will call for a new TPS and a IAT to my trusted provider.
While it arrives I'll be hollowing out the CAT and testing all the vacuum lines.

The CPS would be OK or the Jeep wouldn't go too much far, isn't it?
The CTS is a new one, becouse I slammed the old while working on the engine... I ended changing even the radiator cap (very important).

One question... The carbon vapor canister stuff... is such a needed thing? I don't know if this s*t is in good shape, I thing it misses about 2 or 3 parts of it comparing to the YJ one (The bottom cap, by exmpl. The car had a big crash from the bottom like it jumped hard)

The rear main seal can be changed without lowering the CrankShaft? I forgot changing it and now the engine is pouring lots of oil around the rear side of pan.

Thanks,
Sergio Rius Rodriguez
http://saposysalamandras.dyndns.org

 

[jeeperjohn]

The carbon cannister is important for a vehicle that must pass a smog test. It's best to use it if you can. If the can is not in place, the computer should give a code. The rear main seal can be replaced without lowering the crankshaft but it is not easy to replace. On a non lifted xj you will need to lower the front axle enough to get the oil pan removed. The seal is a two part seal and can be replaced with the oil pan out.

 

[rsalemi]

No one has suggested a lean condition? I would build an adjustable MAP sensor and richen up the fuel to test it out.
My 4.0 with K&N and Borla headers needed more fuel to perform properly. assuming no vacumn leaks I'd try building an adjustable MAP - lean condition causes quick warm up and hot exhaust - which sounds like what you describe. See Dino's page for the MAP sensor info.

 

[Dr. Dyno]

No one has suggested a lean condition?

With an O2 sensor reading of 0.8v I think that's unlikely. His engine's running slightly rich. This could be because of low vacuum (clogged cat, vacuum leak), because one of the load sensors (TPS more likely, MAP sensor unlikely) is telling the PCM that the engine is under more load than it really is, or because one of the other sensors (CTS, MAT) is telling the PCM that the engine's cold or still in the warm-up phase (not allowing the PCM to go into closed loop).

 

[Rapoza]

Today I wired the O2 sensor to my multimeter and tested.
As you start the engine cold, reads 0,45v during less than a minute.
After that, the value starts changing (every half second) from 0,2 to 0,8 aprox while in iddling (It seems to me that stays more on 0,8 values, but perhaps is paranoia).
Running the car, as you push the pedal it reads below 0,45 (0,1 around) and as it is gaining speed (half pedal and little load of slight hill) moves thru 0,80 and varies 0,7-0,8-0,7-1,0 and such.

A friend (Industrial engineer):lecture: told me today that if the exhaust was clogged the car would be having a severe lack of power. :nono:And he states that the car has a big engine and ence it has to drink a lot, so 11 mpg is normal.

I'm very confused, very very confused... At the end I will sell the Wrangler, the Cherokee and the Maverick and buying a Mercedes G. :bawl::bawl:

Saludos,
Sergio Rius Rodriguez
http://saposysalamandras.dyndns.org

 

[Dr. Dyno]

And he states that the car has a big engine and ence it has to drink a lot, so 11 mpg is normal.

My 4.6 stroker averages 17 miles per US gallon or 14L/100km so 11mpg from a 4.0 definitely is NOT normal. You should be able to at least match that or do better. I drive a bit like Michael Schumacher so with a more gentle driving style even I could improve on that.
BTW, your O2 sensor is functioning normally.
Check all the things that I listed. You might also want to make sure there isn't something else adding rolling resistance to the vehicle e.g. binding brakes, tire pressures too low, 'cause this makes the engine work harder.