Engine performance drops 50% at least when outside temp is over 75F

[CaptainXL]

Has anyone noticed this? It seems worse on humid days. I thought it only happened on 90F+ days but I am feeling it much more this year. Basically it will run great with a lot of power until a certain temp is reached outside. Seems to be around 72-76F and I have to floor it just to go anywhere.

 

[tbyoda]

How many miles you got? What have you done to try and fix? I am just guessing but you may have a clogged cat. But just a guess. You got a check eng light on? Got to autozone and have them check for codes.

 

[CaptainXL]

How many miles you got? What have you done to try and fix? I am just guessing but you may have a clogged cat. But just a guess. You got a check eng light on? Got to autozone and have them check for codes.

129,000 miles. You know it does seem like a clogged cat but I did a pressure test and it tested good. It's always been doggy during hot and humid weather. Just noticing it more this year. If I drive it when it's cooler than 72 then it takes off like a rocket. Anything over and I need to floor it to get up to any speed. Is it always like this? I don't know for sure. But it seems to be affected by humidity more. Seems like a granny in her car could beat me to 45mph.

Unfortunately I have no check engine lights on or codes stored. Engine running fine otherwise and all tuned up.

Will check the fuel trims tomorrow and see what we can see. It's just a very strange sensation. Feels like I am towing my trailer.

So I take it that because no one is speaking up that no one is experiencing a drastic reduction in power in hot and humid conditions starting at 75F? Huh... I think we got a good one here.

 

[Wooluf1952]

You didn't say, so I'll ask: Are you getting the jet engine sound from the fan?

 

[CaptainXL]

You didn't say, so I'll ask: Are you getting the jet engine sound from the fan?

No, no no. I got a new Dorman fan clutch last year. I know exactly the noise you are talking about but I don't have it.

Also wanted to add that turning on AC does little to change the reduction in power.

 

[HARDTRAILZ]

Think mine runs better when its hot out actually.

 

[jimmyjam]

check what your timing advance looks like when it boggs down

 

[triz]

No your not the only one. Even when you stomp it you get more sound then movement. She is a bit sluggish when it gets hot and humid which is what it was today.

I may try another one of my products PI Performance Improver.

 

[CaptainXL]

Hmm. Just trying to think about what could affect timing when the weather gets hotter yet wouldn't throw a code.

I will check all that out tomorrow and a few other things as well. Using my Torque app on Android.

 

[Berzerk]

It was 90+ here in Northern Texas today when I left work in the Trailblazer and all was normal, no differance than 2-3 months ago when the weather was much cooler.
Seems like a clogged cat would show the same symptoms no matter what the ambient air temp was but I'm no expert.
Maybe the computer is getting incorrect input from the sensor in the air intake?

Another thought, does this happen as soon as you start the truck up in warmer weather or does it occur after the truck has rached normal operating temp?
If it's the latter than it would seem likely that a component is fatiguing under heat soak.

 

[CaptainXL]

Maybe the computer is getting incorrect input from the sensor in the air intake?

Now this could be something. I replaced the IAT sensor a couple years ago to troubleshoot other things. It was cheap to replace.

I guess it's possible I got a bad one. But again there is no code. It will however throw a code if I disconnect it. My scan tool has always shown the IAT temps as 20-50 degrees higher than the outside ambient temp. I just assumed this was because the plumbing being above the exhaust.

Also of interest. Not entirely sure how it works but just got done reading an article stating that the IAT affects timing.

The problem is predictable (Great here we go again, it's humid and over 75 today) type of thing. It happens driving away right after startup all the way and through warmup. In other words it happens during all times of engine operation. Open loop, closed loop, etc.

 

[CaptainXL]

I did a bunch of searching and found nothing related. Every search I did just turned up people saying:

"Oh, it's normal...in hotter weather that just happens."

I would agree with this generalization but the problem I have is that 75F isn't blazing hot outside. Heck the sun isn't even shining on the hood! It isn't that hot.

Found these TSB's for Ford engines. Very interesting. Now I wonder if my PCM is malfunctioning. It's interesting to note that members here that have 2006 and above report no issues.


15431 - LACK OF POWER IN HIGH AMBIENT TEMPERATURES
Some 1999-2002 Expedition and F-150 vehicles equipped with 5.4L 2V engine may exhibit a lack of power condition when the vehicle is operated in ambient temperatures above 100 degrees F, particularly during stop-and-go driving. By design, the PCM calibration retards the ignition timing to prevent detonation when the inlet air temperature (IAT) reaches temperatures above 140 degrees F. If the lack of power condition occurs only when the IAT is above 140 degrees F, do not replace parts in an attempt to service. Engineering has developed a new calibration which will be available early in the first quarter of 2002. If the condition exists in other temperature ranges, proceed with normal diagnostics.

15630 - LACKS POWER IN HIGH TEMPERATURES - REPROGRAM PCM
Some 2000-2002 Expeditions equipped with a 5.4L 2V engine may exhibit a lack of power condition when operated in ambient temperatures above 100 degrees F, particularly during stop-and-go driving. This may be due to PCM calibration, which retards the ignition timing to prevent detonation when the inlet air temperature (IAT) reaches above 140 degrees F. A new calibration is available to service this condition. If the condition occurs only when the IAT is above 140 degrees F, reprogram the PCM to the latest level via the just-in-time process if your WDS communicates w/Fordstar. Also obtain calibrations on the Ford Professional Technician Society (PTS) website - select 'WDS' then 'PCM reprogramming' and click 'Instructions' for downloading. Calibrations are scheduled to be included in WDS release B17.10.

 

[Playsinsnow]

I don't know CaptainXL, doesn't sound "normal". I've driven all day through just about every condition I can think of and 75 and cloudy sounds pretty close to optimal conditions to me. If the truck has been running all day I could maybe see it becoming sluggish but not for at least a few hours depending on humidity and exhaust conditions at that temp.

 

[AtlWrk]

IATs 20-50 degrees above ambient sounds high but I could be mistaken--it's been a while since I've scanned for that. What are the actual temperatures: ambient, IAT at standstill, IAT at speed? Is your intake stock? Filter? Other modifications (efans, etc) that would be affecting underhood temps?

 

[C-ya]

My IAT temps are usually 5-10 degrees higher than ambient. If the IAT feeds into the timing circuit, then that sounds like a great starting point. I'll try to remember to get some readings today while moving and standing when I get home and it is at temp.

Of course, today you should be good since the temps will be lower!

 

[jimmyjam]

i expect IAT to be about 10-20 deg above ambient while moving when there is airflow though the engine compartment. when idling it can get pretty high, and it takes a couple minutes for it to cool down after beginning to move, but if you are seeing 20-50 deg over while highway driving then something is going on there.

and FYI, according to HPTuners, the ecm starts pulling timing when the iat goes over 113 deg

**edit well just looked at the i6 stock tune, it pulls a lot less timing than my v8 tune so

 

[CaptainXL]

Driving today the IAT was at 100+ when the outside ambient was 74F

 

[gmcman]

You know...there are some days and this happens rarely, but when it's hot, and I'm laying into it I get dismal acceleration and a loud intake growl. Could very well be an aging IAT.

Something to try, rig up a coffee can or similar and fill it with ice cubes and pull the IAT from the intake and secure it under the lid of the can. Should last for a little while and see what happens.

 

[Blckshdw]

Thought of this thread on the way to work this morning, so took a peak at mine after it got up to operating temp. 81 degrees ambient, 91 degrees at the IAT sensor while cruising 40+mph. Bumped up to 96 when sitting in red light traffic. Dropped back down to 91 with about a minute of steady cruising speed. Mods I have are a gutted air box, and home brew silicone intake.

Any members in your area, or neighbors you're friendly with, that would swap IATs with you maybe?

 

[gmcman]

Driving into work, ambient temp is 67, IAT is 84. Parked for 5 min idling, IAT is 98. The MAP and IAT pretty much hold hands, MAP has a big influence on timing as well. Idling 10 min IAT is 105. In your case a 50 deg swing while driving is big. Have you checked the electrical connection for the IAT sensor?

 

[Blckshdw]

Driving into work, ambient temp is 67, IAT is 84. Parked for 5 min idling, IAT is 98. The MAP and IAT pretty much hold hands, MAP has a big influence on timing as well. Idling 10 min IAT is 105. In your case a 50 deg swing while driving is big. Have you checked the electrical connection for the IAT sensor?

Now you've got me curious to see what mine does sitting idle that long, since our temps are a bit higher down here. If this was last week (before all the schools were out) that would be easy to check during the commute.

 

[jimmyjam]

in heavy, bumper to bumper traffic, it goes sky high. 150+ is not out of the question. because you're sucking in air from the engine compartment, and there is nothing you can do about it. a FWI helps a little but not much when you are standing still. for example waiting in the staging lanes at the racetrack expect to get heatsoaked quickly and it won't cool off until you are down the track...

 

[CaptainXL]

I did a log for a couple hours of city driving and noticed nothing abnormal about the fuel trims or O2 readings.

This is what I found...

MAP readings were consistently 20 in drive stopped at a light. When I turned to AC on it dropped to 17. RPM steady at 605-617ish.

Timing advance in drive while stopped at a light is always at +10 degrees

When accelerating it goes up to +32 but no higher even if floored. Not sure if this is normal.

A few times it seemed to drop to 0 but that could have been my scan tool.

IAT's always seem to be 20-30F higher than outside ambient. It was 81 today and the IAT read 117F when stopped at a light. The IAT temps never come close to ambient, even when driving over 45mph. The closest it gets is within 20F. So being 81F it will never go below 100F.

Seeing how I just got this IAT I think it is working fine. And from what I gather reading about the subject this is normal. It depends on where the IAT is located in the intake path. Closer to the inlet near the filter and it should be lower. More details to follow. Got a bunch more data to compile. Still looking through the logs. I am logging a ton of events.

 

[CaptainXL]

Did some more driving today. Noticed the timing advance was all over the place. At times it would stay around 10 when accelerating and would not advance. At other times when decelerating the timing would shoot up to 53. Just doesn't make sense.

The truck drove halfway decent today. It was 72 out. Noticed the IAT got up to 120F at lights. Still gonna keep checking stuff.

 

[jimmyjam]

iat sounds normal. 10deg spark advance under throttle aint right

View attachment 28880

is the scanner showing knock or knock retard?

 

[CaptainXL]

is the scanner showing knock or knock retard?

Will definitely check on that. Filled up with 93 octane today to see if preignition has something to do with it. The map sensor was replaced a couple years ago. Perhaps it is bad? Pulled a few spark plugs and they are white.

 

[CaptainXL]

Used my scanner this morning and during a 10 mile trip I saw that the knock retard was at 1.1. Knock counter is at 163. I think it keeps adding up since the last battery disconnect. It never incremented at all.

The timing advanced showed a nice predictable increase when the rpms went up. Seems to work fine now. It was 65F this morning.

 

[gmcman]

What is the failure rate on the knock sensors? Worth a try checking the connections for any corrosion.

 

[gmcman]

Something to consider, if you have a tank of 87, then fill up with 93 and drive it like you stole it....your ECM may revert back to the low octane map until the next fill up. You need to take it easy or just fill up with about 7-8 gallons then refill again with 93 when empty.

In stock trim the ECM senses a fill up and opens the door for the higher octane table. If it sees a lot of knock then it will use the low table. I'm not sure how long it takes to switch or how much fuel is needed on fill up to change this. Gives the ECM a narrower parameter to work with for quick adjustments.

 

[gmcman]

Capt, I drove mine today with my scan tool and I had 10-15 deg advance under heavy load between 1500-3000 RPM's, generally in 3rd or 4th with high throttle setting not dropping a gear. About 40-50 dropping down to 3rd I would have 15-20 as the RPM's increased. WOT around 4500+ I would have low to mid 20's.

There were times it would drop to about 9 deg around 40-45 mph if I kept accelerating in 4th with a high load before it downshifted. Idle is 15-16 with occasional dips to 13.

 

[gmcman]

Also with my water pump making noise I say it's a fair guess that it could easily mess with the knock sensors, especially being in the water jackets. I'm glad you brought this up as I will test before and after the water pump change.

 

[ScarabEpic22]

On regular (87 octane), these I6s dont take a lot of timing under WOT/PE. Watch you camshaft modifier tables, all of a sudden you'll get 10-20* of timing out of nowhere and it's because MAP went above 70kPa and you're getting a 2x multiplier on the spark cam values.

Mine's still a dog when the IATs heat up, if it didnt spend it's winters in Montana Id do a FWI-style intake on it and get the IATs much closer to ambient.

 

[CaptainXL]

Also with my water pump making noise I say it's a fair guess that it could easily mess with the knock sensors, especially being in the water jackets. I'm glad you brought this up as I will test before and after the water pump change.

Interesting that you bring up the water pump. I opened the hood yesterday and swear I could hear a very faint "tink, tink, tink". Like once every couple seconds. Perhaps its starting to go and being picked up by the knock sensor as a knock.

So I got the 93 octane in there and i was looking at the knock counter and knock retard. Interestingly I saw no knocks on the counter but the knock retard showed that it regularly pulled about 8 degrees while acclerating at a modest clip. Its just weird. Was reading some articles that suggest the knock sensors are a preventive maintenance item and should be replaced every 100k.

Erik, thats interesting. Kind of confirms what I am sensing. But doesnt explain why I have knock retard. Perhaps IAT retard is categorized as knock retard.

 

[gmcman]

I replaced my water pump today but haven't driven it, only idled for about 10 min.....I want to say the tapping I have heard is no longer present. The exhaust leak is still there but my initial observation is I have muted a noise so hopefully I can confirm it. I would get an occasional retard down around 8 deg also on a good accel so it's happening to me also, depends on RPM, gear, etc.....could be normal..not sure.

 

[gmcman]

Update.....removed driveshaft this AM to have the balance checked, bad vibe from 65-75 since I had it shortened so I couldn't drive it but on a cold start I didn't hear the knocking or light tapping so my fingers are crossed. The way I see it is if I can hear a light knock standing outside the vehicle, the knock sensors can surely hear it, and they react before any knock is plainly audible, or just react before you can realize there is a knock.

I had 15-16 deg adv at idle so I can at least try to compare that value when I return.

 

[gmcman]

Another update.....w/o driveshaft in using 4WD I was able to powerbrake and while standing still, I revved it up to about 1800-2000 RPM's and the spark advance was between 20-25 deg under a good load. Not much to go on since I'm not on the road but under that load before I was getting around 8-10 deg advance.

Idle is around 15 deg but it creeps up to 20 then back down, used to hover between 14-16 and not try to climb. I will pull the battery cable while I'm out and let it all reset. After the water pump change it stumbles slightly when the A/C kicks on and likely not use to the added load. The old water pump impeller basically freewheeled when I spun it.

Hopefully we're on to something.

 

[gmcman]

Well, after the ECM reset, new water pump.....it's quieter but the ignition timing didn't change too much. I never really paid too much attention to it before so I don't have much to go in. What I can say Capt'n is at WOT from 4K on I have 23-26 deg advance, generally 25-26 if that helps any, this was in 2nd gear.

The motor is a little bit quieter anyway.....

 

[CaptainXL]

I have that much advance as well. Just not on every drive when I should be seeing it. Trying to determine if its temp related + IAT or bad knock sensors or something else. Will be disconnecting the knock sensors next to definitely see if its knock sensor related.

 

[gmcman]

I'm kicking myself now but it's because I already was tearing into it when I was thinking on the knock sensors...but I wish I had hooked up a scope to the knock sensor and noted the change after the pump change. I like trying to dig into symptoms like this but I missed the bus this time.