4.0 Tuning exercise: phase 1

[Dr. Dyno]

Besides how much go fasting do you do below 3k?

Most of it actually. With my 4.6 stroker I seldom feel the need to go above 2500rpm 'cause it's producing 95% of maximum torque at that engine speed. Even at 1500rpm it's producing 89% of maximum torque so I can tool around with the engine at low rpm for good gas mileage and still go fast (84mph in 5th gear = 2500rpm).

 

[WheelinJR]

There's a thread on here mentioning a guy using an Apexi SAFC II to tune his Jeeps AFR's more accurately, might be worth looking into.

 

[Dr. Dyno]

That was Talyn aka SilverXJ.

 

[mmag1982]

hello everyone,

In my endless quest to eliminate pinging in my XJ I noticed something a odd.

My air fuel ratio indicates 14.9 to 15.1 during WARMUP !, i start the car from a complete cold start, it fires up with a fairly smooth idle and the usual elevated RPM but runs at this very learn AFR, it takes a little longer than usual for the temp gauge to reach the middle

Everything i know about cars tells me that it should run RICH at warm up which is an open loop mode.

my fuel system is fine and runs at deep as 11:1 during WOT, idle quality is fine,

and temp gauge works normal which means its getting a meaningful signal from somewhere,

how come its running that lean during warm up? I am thinking its related to the pinging issue

 

[Dr. Dyno]

It sounds like the coolant temp. sensor inside the t'stat housing that sends a signal to the ECU (and triggers the electric fan) could be faulty. Measure the resistance across the two wires going to it when the engine's cold and post the result.

 

[mmag1982]

yes , will do,
but just a thought: how come the temp gauge is getting a normal reading? does n;t the coolant temp sensor send that signal?

 

[DeftwillP]

There are two different temp sensors IIRC. One for the computer and one for the gauges.

 

[Dr. Dyno]

There are two different temp sensors IIRC. One for the computer and one for the gauges.

What he said. The gauge sending unit has only a single wire connector going to it whereas the CTS has a two-wire connector so that's how you tell the difference.

 

[mmag1982]

didnt know that!..thanks DeftwillP , and where is it , this gauge sending unit? definitely not in the thermostat housing?

 

[Talyn]

There are two different temp sensors IIRC. One for the computer and one for the gauges.

Not on the 97+. There is only one temp sensor. Its the one in the t-stat. The gauges are fed from the PCM.

 

[Keithmania]

I thought the 2 sensor set up was a Renix and OBDI thing, and when OBDII was phased in it went to a single sensor was use to feed the ecu and the gauges...

 

[O-Gauge Steamer]

^^Correct, a single sensor in the T-Stat housing supplies the information to the PCM which in turn drives everything.

Zanesville... I lived in Elyria for 8 years (1987-1995) in one of the many century homes that litter the landscape. Wish I had that house now!

 

[Keithmania]

@o-gauge, dude, houses are cheap here. There are so many listings for less than 50K its crazy. Of course fixer upper comes in the titles of most of those.

 

[O-Gauge Steamer]

I know. In 1987 I paid $56k for my 3,500 square foot, built in 1865 century home.

Don't think I haven't thought about moving back. I'm retired so, finding a job is not an issue. Good thing I woulf not need one isn't it?

 

[cruiser54]

I thought the 2 sensor set up was a Renix and OBDI thing, and when OBDII was phased in it went to a single sensor was use to feed the ecu and the gauges...

Renix had a temp sender at the back of the head for the gauge and a temp sensor for the electric fan in the bottom left of the radiator.

Early to mid 90s had temp sender in back of head and temp sensor for fan in the thermostat housing.

 

[FunkRider]

hello everyone,

In my endless quest to eliminate pinging in my XJ I noticed something a odd.

My air fuel ratio indicates 14.9 to 15.1 during WARMUP !, i start the car from a complete cold start, it fires up with a fairly smooth idle and the usual elevated RPM but runs at this very learn AFR, it takes a little longer than usual for the temp gauge to reach the middle

Everything i know about cars tells me that it should run RICH at warm up which is an open loop mode.

my fuel system is fine and runs at deep as 11:1 during WOT, idle quality is fine,

and temp gauge works normal which means its getting a meaningful signal from somewhere,

how come its running that lean during warm up? I am thinking its related to the pinging issue

14.9-15.1 is not lean for startup on later OBDII vehicles. I assume you aren't seeing cold start temps much below freezing. If you tried a cold start in say -10F (-23C) you would see some richer AFR readings for a few seconds while things warmed up. Fuel injectors are pretty good at injecting a useable spray of fuel even at cold temps. If the spray is good then so will atomization. If atomization is good then you don't need an excess of fuel since it won't be puddled on the port walls and intake valve. Remember you are seeing O2 readings from burned exhaust gases. If you could compare injector duty cycles between a cold start and operating temp idle you would see a huge difference in how much fuel it is actually burning. The OEM tuning has it running that AFR for emissions reasons to get the catylist up to working temperature. AFR's above stoichiometric 14.7 see a huge decrease in HC with a mild increase of NOx as long as things stay below 15.5 or so.

In the old days of carburetors engines actually ran VERY rich just to keep them running during cold starts because a carb can not adapt fueling between a cold start and operating temp idle. The solution was a choke valve to choke the engines air supply down to richen the effective AFR due to the cold air being more dense and because carbureted fuel atomization mostly sucks at cold temps.

 

[mmag1982]

@ funkrider: makes sense, thats most well detailed explanation I've seen. thanks.

As for my updates, I had one hell of job tonight as i started installing my flow-daddy header.

Removing the intake and exhaust manifolds was the most painful, frustrating, complicated job I've ever done on a car. :banghead::banghead:
If i can only get hold of the idiot who designed the way they fit. here are are some photos and what I learned as well.

- The most painful part of the job was reaching the 4 bolts that hold the intake/ exhaust manifolds together, they are below the intake manifold and nearly impossible to reach.

- The way I finally figured it out is to reach from the SIDE of the manifold not from below as the manual says. I used a 14mm socket with something like cv joint, and an L shaped extension. It was 1 hr of using only my sense of touch as the intake manifold completely blocked the view, I reached from the side of the manifold with my fingers to seat the socket, then plugged in the extension arm.

- The nice thing is that using this method I didn't have to remove the down pipe again as the manual says.

- I am planning to heat shield the intake before installing it as the OEM is really stupid, I cannot imagine what the intake charge temp will be with the exhaust sitting manifold sitting less than 5mm below the intake. No wonder its pinging!!

I have a 62mm BBK throttle body and 24 lb hesco injectors on the way as well. Will update with progress.

 

[Talyn]

You don't need larger injectors on a mostly stock engine. Especially since your WOT AFRs were very rich. You are just going to piss the computer off and may see a loping idle in the first minute of cold start.

 

[cruiser54]

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.

Gradon- Did you receive my PM about the turbo/supercharger within the last week?

 

[gradon]

got it and replied