Fuel economy down, soot up, power fine

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

Been trying to figure this one out for about three weeks and I'm getting nowhere with it. Hopefully someone will have some ideas.

Noticed a drop in fuel economy (miles driven divided by gallons pumped; the EVIC is totally untrustworthy in this regard) a while back to around a 20mpg average from the usual 23mpg-24mpg. This happened at the same time I observed a significant uptick in soot under moderate to heavy throttle - almost a rolling coal level of soot. Power and responsiveness feel about normal.

There are no sounds of an intake leak, and I've checked (where possible) with a stethoscope at likely locations with no results. Tightened everything down just to be safe, though. Did not observe leaks at the intercooler in testing with soapy water. MAP sensor needed a cleaning (as usual), but doing so made no appreciable difference.

EGR and FCV are deleted with a Weeks kit (Stage 1 & 2) installed. PCV to intake hose looks fine (it was replaced about 6 months ago). Intake adapter hasn't budged. MAF is connected, largely just to keep crud out of the connector.

We have been having triple-digit temperatures here, so A/C use has been near-constant. However, we did get a week of milder weather, and I drove for pretty much the entire time with the A/C off. There was a slight difference, but only about as much as you'd expect from not using the A/C. It also leaves the soot uptick unexplained.

I probably have a front driveshaft U-joint that needs replacement (need to get under there and look today), but that shouldn't have much if anything to do with it.

Something sensor-related, possibly? What's throwing me is that everything is running basically as expected otherwise.

rancherman · **Posted:** Sat Aug 04, 2018 9:43 am

check/replace the air filter first.

papaindigo · **Posted:** Sat Aug 04, 2018 9:49 am

Clean MAP sensor (back of valve cover under wiring bundle); perform "Italian" tuneup (get engine to operating temp; do several full throttle accelerations up a slight grade similar to Interstate on ramp to free up turbo vanes); check air box to turbo hose for tear on bottom just in front of turbo; add a good does of PowerService silver or equivalent to next full tank of fuel; if your temp gauge is not just slightly left of dead vertical replace thermostat (do not use inline) as running cold/cool can cost 10-20% mpg; after a run with minimal brake use check for hot wheels (dragging brake shoes)

WWDiesel · **Posted:** Sat Aug 04, 2018 11:14 am

Check the CAC (intercooler) real close, they have been known to develop small cracks and / or leak boost where the tanks are connected. :idea:

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

Running through everyone's suggestions in order:

rancherman wrote:

check/replace the air filter first.

Forgot to mention: this was done about 6 to 8 weeks ago. It's still clean.

papaindigo wrote:

Clean MAP sensor (back of valve cover under wiring bundle); perform "Italian" tuneup (get engine to operating temp; do several full throttle accelerations up a slight grade similar to Interstate on ramp to free up turbo vanes); check air box to turbo hose for tear on bottom just in front of turbo; add a good does of PowerService silver or equivalent to next full tank of fuel; if your temp gauge is not just slightly left of dead vertical replace thermostat (do not use inline) as running cold/cool can cost 10-20% mpg; after a run with minimal brake use check for hot wheels (dragging brake shoes)

MAP sensor has been cleaned a couple of times. No change.

Italian tuneup == tons of soot. Been trying that one on and off with the same result since I first noticed the issue about 3 weeks ago.

Airbox to turbo hose looked OK when I checked it, but will re-inspect.

Have not run a fuel system cleaner through it; will dump some in tomorrow when I fill it with this week's tank.

Thermostat is an HDS Model 001 installed around December and is working fine at 193°F.

Dragging brakes: hadn't thought of this, but I do have a warped rotor (driver's side front, IIRC) that's getting replaced along with the other three and pads next week when the lift goes in. Could be a possibility. Will investigate; if that looks like it might reasonably be, I'll hold off on doing anything about it until it's time to do suspension.

WWDiesel wrote:

Check the CAC (intercooler) real close, they have been known to develop small cracks and / or leak boost where the tanks are connected. :roll:

I'll check it again. Frankly, having just replaced the radiator, I'm not desperate to open the front end up again - but if that's the cause, there isn't a whole lot of choice in the matter.

WWDiesel · **Posted:** Sat Aug 04, 2018 3:16 pm

Dragging brakes can cause some loss of fuel mileage, but will not cause excessive black smoke when accelerating.
That is a huge sign of low boost or over fueling!

Do you have a boost gauge? It can tell you a lot.
Some other things to check are:
the small plastic vacuum line from the turbo vacuum modulator valve over to the turbo vane controller. One member found his had melted and / or cracked a few years back and it was causing low boost. See this older post:> viewtopic.php?p=682128#p682128

check stroke on turbo vanes and make sure there is no sticking going on that would prevent full vane movement.
check and make sure you have full vacuum at turbo modulator control station.

turbo modulator solenoid may be bad, you can test it by bypassing it temporarily.
These are the instructions:

Quote:

Turbo Vacuum solenoid test procedure

Failure of the vacuum reservoir solenoid (a.k.a. solenoid secondary runner valve per the parts fiche PN(PN 4606226AC) ) can produce several MIL/CEL codes and result is turbo boost problems. A temporary solution and diagnosis is to bypass that solenoid by rerouting vacuum lines as in the picture below:

By disconnecting the little hose from where the red arrow is and re-plugged it where the yellow arrow is (VAC port). If that solves the problem then leave the hoses in the new/temporary configuration and order a replacement solenoid. In the interim the vehicle may be driven; the CEL will remain until you replace the on/off solenoid. The only benefit that part provides is overnight storage of vacuum in the plastic reservoir so the turbo has vacuum immediately during the start. Without it you have a 2-10 second wait before the engine vacuum pump evacs the lines enough for the turbo vanes to move. Once the replacement solenoid is installed put the hose(s) back the way they were originally.

GDE's writeup for this says "By-passing of the on/off solenoid is very straight forward. Trace the vacuum line output from the black plastic reservoir to the input of the on/off solenoid. Remove this vacuum line and plug it directly into the turbo EVM on the port labeled "VAC". The turbo EVM is the one with the blue rubber isolator and vacuum line running directly to turbo."

Hopefully these pictures and diagrams will help: :SOMBRERO:

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

WWDiesel wrote:

Dragging brakes can cause some loss of fuel mileage, but will not cause excessive black smoke when accelerating.
That is a huge sign of low boost or over fueling!

That was my thought. This thing is great for multilayered problems

Quote:

Do you have a boost gauge? It can tell you a lot.

I do not. Plan is to install one at some point, but need to get the current pile of projects out of the way first - I'm starting to packrat parts rather than putting them on the KJ.

Quote:

Some other things to check are:
the small plastic vacuum line from the turbo vacuum modulator valve over to the turbo vane controller. One member found his had melted and / or cracked a few years back and it was causing low boost. See this older post:> viewtopic.php?p=682128#p682128

check stroke on turbo vanes and make sure there is no sticking going on that would prevent full vane movement.
check and make sure you have full vacuum at turbo modulator control station.

turbo modulator solenoid may be bad, you can test it by bypassing it temporarily.
These are the instructions:

Quote:

Turbo Vacuum solenoid test procedure

Failure of the vacuum reservoir solenoid (a.k.a. solenoid secondary runner valve per the parts fiche PN(PN 4606226AC) ) can produce several MIL/CEL codes and result is turbo boost problems. A temporary solution and diagnosis is to bypass that solenoid by rerouting vacuum lines as in the picture below:

By disconnecting the little hose from where the red arrow is and re-plugged it where the yellow arrow is (VAC port). If that solves the problem then leave the hoses in the new/temporary configuration and order a replacement solenoid. In the interim the vehicle may be driven; the CEL will remain until you replace the on/off solenoid. The only benefit that part provides is overnight storage of vacuum in the plastic reservoir so the turbo has vacuum immediately during the start. Without it you have a 2-10 second wait before the engine vacuum pump evacs the lines enough for the turbo vanes to move. Once the replacement solenoid is installed put the hose(s) back the way they were originally.

GDE's writeup for this says "By-passing of the on/off solenoid is very straight forward. Trace the vacuum line output from the black plastic reservoir to the input of the on/off solenoid. Remove this vacuum line and plug it directly into the turbo EVM on the port labeled "VAC". The turbo EVM is the one with the blue rubber isolator and vacuum line running directly to turbo."

Hopefully these pictures and diagrams will help: :SOMBRERO:

And there's the light bulb moment - I did not check the vacuum actuator or associated plumbing. Will try to later today when it's not 4,000,000 degrees out and see what things look like.

flash7210 · **Posted:** Sat Aug 04, 2018 6:21 pm

Quote:

Will try to later today when it's not 4,000,000 degrees out

Which is the other part or this issue.

It’s HOT out.
Your driving with the AC on all the time.
The intercooler is less efficient.
Etc.

Why I’ll bet your IAT is above 150F.
Point is, the air density is low but the fuel injected is the same.
Therefore, more soot in the exhaust.

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

flash7210 wrote:

Quote:

Will try to later today when it's not 4,000,000 degrees out

Which is the other part or this issue.

It’s HOT out.
Your driving with the AC on all the time.
The intercooler is less efficient.
Etc.

And I agree - except that I get the same results when the ambient temperature drops by 20-25°F and the A/C is not in use during that time. That was the case for nearly a week straight, so was able to compare fairly directly with the much higher temperatures.

Quote:

Why I’ll bet your IAT is above 150F.
Point is, the air density is low but the fuel injected is the same.
Therefore, more soot in the exhaust.

Snorkel time? :SOMBRERO:

But yes, I agree that these can all be contributing factors. However, it's happening across too broad a range of ambient temperatures to definitively pin it on just those factors, IMHO.

dennyb · **Joined:** Wed Aug 13, 2014 4:27 pm **Posts:** 110

Bad rocker(s)? What's your grams/second airflow at idle.

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

dennyb wrote:

Bad rocker(s)? What's your grams/second airflow at idle.

Should that be measured with the engine hot, cold, or both?

I can plug in the OBD-II reader later and take some numbers. Right now the engine is stone-cold from sitting overnight, so if a cold reading is significant it would be good to know that before I go driving around later

k9adv · **Posted:** Mon Aug 06, 2018 10:51 am

Pretty sure i read from cold, start engine, wait at least 60 seconds to note MAF readings.

SJBrooks · **Joined:** Tue Mar 11, 2014 11:01 am **Posts:** 42

k9adv wrote:

Pretty sure i read from cold, start engine, wait at least 60 seconds to note MAF readings.

I too am interested in this reading from my Jeep. What is the proper way to do this?

thanks,

Steve

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

Total non-update: I've done absolutely nothing with this. Ran out of time before starting in on the lift last Wednesday, and the weather has been totally uncooperative as regards finishing that job off since then.

As soon as the front suspension, steering, brakes, and tyres are back on and an alignment's been done I'll pick this up again. Hopefully that will be this weekend, but we're supposed to have thunderstorms for the next few days so we'll see what happens.

mass-hole · **Posted:** Wed Aug 15, 2018 5:09 pm

I know for a fact that the ECU will cut boost at 50C/122F and greater IAT's. If you're in triple digit weather and your running with the A/C on, I can guarentee that your IAT(MAP) sensor is reading at least that high and probably higher. I have a custom intercooler mounted in front of my A/C condenser and still see 40+C on the IAT's just cruising around at 55mph on a 80 degree day. A stock intercooler hiding behind the hot A/C condenser is gunna be HOT.

Even when its cooler out you still may be seeing higher IAT's.

Additionally, I see you have an HDS tstat. I recently switched out my 203F stat for a 180F stat because I had a feeling that my MAP sensor may be getting heat soaked by the aluminum manifold. I can be coasting down a mountain, totally off throttle, and my IAT's will read 15-20C higher than ambient without fail. The jury is still out on whether the cooler tstat helps with IAT's because the temperature outside dropped about the same time. This morning I was in the low 30C range instead of my normal 40+C range. I have a intake air temp gauge that I need to install to verify all of this.

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

mass-hole wrote:

I know for a fact that the ECU will cut boost at 50C/122F and greater IAT's. If you're in triple digit weather and your running with the A/C on, I can guarentee that your IAT(MAP) sensor is reading at least that high and probably higher. I have a custom intercooler mounted in front of my A/C condenser and still see 40+C on the IAT's just cruising around at 55mph on a 80 degree day. A stock intercooler hiding behind the hot A/C condenser is gunna be HOT.

OK, that makes sense. It also tracks with an observation I've had, which is that on cooler days the soot isn't as much of an issue. It's still noticeable, just not as bad as in warmer weather.

Quote:

Even when its cooler out you still may be seeing higher IAT's.

I also have a V6 airbox fitted. That's drawing its air from the underside of the hood, right above the crossmember holding the A/C condenser / intercooler / radiator stack in place. My thought is that this could be a contributing factor, since that location is pretty much exactly where heat from that stack will rise to first. In motion, it seems as though this shouldn't play into things much due to airflow from the front - but it's still going to be heat's first stop as it rises. Hmm.

Quote:

Additionally, I see you have an HDS tstat. I recently switched out my 203F stat for a 180F stat because I had a feeling that my MAP sensor may be getting heat soaked by the aluminum manifold. I can be coasting down a mountain, totally off throttle, and my IAT's will read 15-20C higher than ambient without fail. The jury is still out on whether the cooler tstat helps with IAT's because the temperature outside dropped about the same time. This morning I was in the low 30C range instead of my normal 40+C range. I have a intake air temp gauge that I need to install to verify all of this.

This also makes sense, and I did recently swap out the 203°F thermostat for (IIRC) a 193°F unit. Didn't see a noticeable change in soot, but it's also only a 10°F drop in coolant temperature. If heat soak is playing into this, I can see where that might not be enough of a change to really affect things.

Interesting that you mention heat soak, though. If I drive for long enough (say, 20 minutes) to get the engine thoroughly warmed-up with the temperature gauge at the normal spot just left of centre, switch off, then come back 20-30 minutes later and turn the key without starting, the temperature needle will swing past centre about one-third of the way between normal and hot. Once started, it'll drop down to normal within 10 seconds or so as coolant starts flowing again. Classic indicator of heat soak, so you may be on to something.

casm · **Joined:** Sun Jan 29, 2006 5:05 pm **Posts:** 694

Update on this: lifting the Jeep appears to have fixed the problem.

Well, OK. I'll admit that that's not the true fix - but I don't actually know what resolved it. Having been driving around for the last four days since the lift was finished, though, the problem seems to have gone away.

My best guess is that leaving the ECU without power for several days may have caused it to lose some stored values that were throwing something out of whack with respect to the air / fuel mixture. My second-best guess is that something that has an actual problem got jostled in just the right way that it's no longer happening, but as nothing in the intake / vacuum paths were disturbed (as far as I can remember, anyway), I have no idea what that might be.

Either way, I'll keep an eye on it over the next few days and see what happens. If it recurs, I'll try unplugging the ECU for a couple of days: if that solves it, great; if not, back to the drawing board.

Grotsoldaat · **Posted:** Wed Aug 22, 2018 9:45 am

casm wrote:

Update on this: lifting the Jeep appears to have fixed the problem.

So, it had too much ground effect. Now, when gravity effects it significantly less, fuel does not go porridge and burns easier. But the lack of gravity is making it unstable (steering), so you need to install a spoiler:

WWDiesel · **Posted:** Wed Aug 22, 2018 10:15 am

casm wrote:

Interesting that you mention heat soak, though. If I drive for long enough (say, 20 minutes) to get the engine thoroughly warmed-up with the temperature gauge at the normal spot just left of centre, switch off, then come back 20-30 minutes later and turn the key without starting, the temperature needle will swing past centre about one-third of the way between normal and hot. Once started, it'll drop down to normal within 10 seconds or so as coolant starts flowing again. Classic indicator of heat soak, so you may be on to something.

That statement got my attention and concerns me! :shock:

I have never observed this on my Jeep and I live in a location where we can see 100+ ambient temps coupled with very high humidity.
On mine the temperature gauge always drops slightly or stays the same after I shut it off and restart it 10-15 minutes later even in hot sunshine and high outside air temperatures.
I don't have the OEM plastic engine cover in place, removed it years ago. Not sure if that plays into this or not?

Maybe your temperature sensor is bad? Might be worth a try to replace.

Just curious; Are there any others in very hot climates observing the phenomenon described by casm? :ALONE:

Grotsoldaat · **Posted:** Wed Aug 22, 2018 10:34 am

WWDiesel wrote:

casm wrote:

Interesting that you mention heat soak, though. If I drive for long enough (say, 20 minutes) to get the engine thoroughly warmed-up with the temperature gauge at the normal spot just left of centre, switch off, then come back 20-30 minutes later and turn the key without starting, the temperature needle will swing past centre about one-third of the way between normal and hot. Once started, it'll drop down to normal within 10 seconds or so as coolant starts flowing again. Classic indicator of heat soak, so you may be on to something.

That statement got my attention and concerns me! :shock:

I have never observed this on my Jeep and I live in a location where we can see 100+ ambient temps coupled with very high humidity.
On mine the temperature gauge always drops slightly or stays the same after I shut it off and restart it 10-15 minutes later even in hot sunshine and high outside air temperatures.
I don't have the OEM plastic engine cover in place, removed it years ago. Not sure if that plays into this or not?

Maybe your temperature sensor is bad? Might be worth a try to replace.

Just curious; Are there any others in very hot climates observing the phenomenon described by casm? :ALONE:

Down here in southern Bulgaria summer temperatures go regularly past 90°F, but rarely over 100. My Jeep does similar, if it stands just couple of minutes and my bike (Yamaha FJR 1300) as well and I have considered it normal. It seems to vary in different vehicles and is connected to the location of the sensor.

Fuel economy down, soot up, power fine

Who is online