TomCat39

I remember the title happening years ago on a 4 banger toyota sr5 pickup back in the 90's on me.

We were flying up the highway going up mountains. Not so steep as to be noticable but we were climbing elevation.

Doing between 90 and 110 MPH in 5th gear overdrive, which allowed us to maintain decent RPM. After about 20 minutes or so of climbing, the power started dropping. Downshifted into forth and it didn't improve so we pulled over and I popped the hood to see the cast iron header glowing red hot. We sat there for about 5 minutes or so until the header was pretty much dark again and went on our way never using 5th when climbing and had no issues for the rest of the drive nor for years after.

The engine didn't overheat or any other signs of anything funky when this occurred. The only thing found was the bright red glowing header under the hood. And this was during midday sun, not a cloud in the sky, bright red glowing header.

Anyways, can a wise person explain why or how a bright red hot header robs a motor of it's power? It is not like the exhaust was clogged in any way, just the header was a bit overheated.

To this day, I do not understand why that robs the motor of power even though I experienced it first hand back in the day.

holmesnmanny

Sounds like the exhaust was somehow backed up.

TheShodan

iTrader: (14)

Heh.. that's cute, but umm. No. Nothing is "backed up" like some sort of clog in a bathroom. Especially when EGTs are about 1400*F on that exhaust manifold.

What happening is that ignition timing is retarded based upon the load of the engine. You're basically "lugging" the engine; In effect, putting too much engine load (from climbing up the mountain) in too high of a gear. When you lug the engine like that, it causes timing to be retarded, the engine struggles and you lose power.

Lugging an engine is like hammering the engine parts with every explosion in a cylinder. It racks on the rod bearing/journals, makes the pistons slap the side of the cylinders hard, and if is done enough, could probably break piston rings. It also creates a hammer effect all the way through the drivetrain. There are springs in the friction disk (of the clutch) which takes up some of this hammering, but they will only take so much before they wear out as well. This causes premature wear all the way around. It's not like it will wear out tomorrow, but it will cause wear over time. If you want your car to last a while, you don't want to be doing this.

http://www.roadandtrack.com/car-cult...ad-for-engine/

TomCat39

I understand all of this. And I do not disagree with the fact we were overloading/lugging the engine even though it didn't sound like it with the high RPM.

I am wondering why the effects are not immediate from loading/lugging the engine but instead took about 20 minutes of this before the power loss started to occur?

I would honestly think the power loss of lugging the engine would be pretty close to instant.

tony_2018

Good discussion, hope more will chime in.

holmesnmanny

You've never heard of a cat going bad and clogging up ? It happens more than you think. To test you would either open it up or pull the oxygen sensor to let it breathe and it would be good again.

When metal gets hot it expands and that could plug up any small hole that was existing before that.

Not saying it's definitely happening but that could be a reason.

TheShodan

iTrader: (14)

You're going to experience a code before a catalytic converter gets to that degree of being "clogged", and it still won't cause a retardation of ignition timing like that. It also wouldn't go away after a period of time either.

That engine was lugging around for a while. When that happens, you won't experience the power loss for some time while it's occurring. It takes several instances of you lugging the engine for it to be feel like an actual power loss. Make sure you stay in a lower gear. check your timing, check your plugs and keep moving on.

TomCat39

By definition, we weren't lugging the engine. The definition provided in both the video they reference and the article you posted says flooring it in low RPM (1500 RPM or so).

Our RPM was high, like 4000 or so in overdrive. We were definitely loading the engine though (overloading more than likely) so I suspect it was very much causing the same results/behavior as lugging the engine but at 4000 rpm instead of 1500.

Of note, nothing sounded funny in the engine when the power loss began to occur, it just didn't have the oomph it did just 10 seconds before. Very much like a partially clogged exhaust. But as was pointed out, clogged exhaust doesn't go away by letting everything cool for 5 minutes.

So if it's not actual "low speed pre ignition" from lugging the engine (not saying it isn't but just humoring the idea).... What affect of the overheated header would act like a virtual clog?

Even though the temp gauge on the dash didn't show overheat status, seeing the header glowing as severely as it was, I tend to think the exhaust valves and ports were overheated a bit too. Would all this extra heat restrict exhaust flow from the head through the header? Act like some kind of invisible barrier?

Just trying to humor the idea of the clog theory that goes away just by letting the engine cool 5 minutes.

holmesnmanny

Depends on if the car has a downstream oxygen sensor.

The fact that your car was running fine up until that point could point to there being just enough gap to allow the engine to breathe. As metal gets hot it expands and it could plug up that hole.

Again, not saying for sure this is what's happening but it's a thought.

TheShodan

iTrader: (14)

You can't go by just the definition, any driving in a high gear after a certain degree of incline can create the same condition as though it were on a flat surface. Elevation plays a factor as well. These definitions were a basis to start diagnosis, but other factors do come into play.

Now you're getting it.. when in "overdrive" gearing, that's basically "lugging" the engine if underspeed or at an incline

The change in pitch in engine load is what you'd hear more than necessarily a change in exhaust note. Again, without a clear video of a reenactment of the condition, I can't complete confirm. But based upon deductive reasoning and the symptoms you've stated, you're "lugging" the engine.

That's for home-slice to answer.

You're looking at coolant temperature, which has nothing to do with Exhaust Gas Temperature (EGT gauge). That is a gauge that would show you that your timing has changed from the overload of the engine in a high gear. With the car moving, the coolant temp would change very little if any. If you don't have an EGT gauge, well, then you're not going to know exactly how much timing had retarded. Only the sound and power loss would be the best determining factors, which you've already seen.

I gotcha.

TheShodan

iTrader: (14)

They all do. that's irrelevant. One sensor sends a voltage signal to the ECU and the secondary one sends a second voltage signal when the car is warmed up. If the disparity between the two voltages is under a certain ohms, then it throws a check engine light. That's how Hondas always were ahead of the ULEV game for over 20 years. The phenomenon you're describing would cause a CEL illumination




This individual's recent question on H-T addresses this exact premise
https://honda-tech.com/forums/tech-m...-1-3v-3295714/

Hole? I thought your theory was based upon a clog, not a physical hole. Elaborate, please.

TomCat39

To be fair, doesn't it depend on the year if it has a downstream sensor? OBD1 Honda's only have upstream sensors (95 and earlier).

Remember I said it was in the 90's. To be precise it was a used Toyota SR5 we purchased and it was before 1996 as that was when I moved to Florida. So either bought in 94 or 95 and it was used when we got it with 184,000 miles on it. I don't remember exactly but that is a bit more clear than just "the 90's".

Regardless, thank you for the explanation on overloading/lugging the engine. It fits like a glove so I am sure that's exactly what we did to the engine. I am just glad we only did it that once for a short duration so the engine wasn't damaged like it could have been.

TheShodan

iTrader: (14)

It still isn't all that relevant, because the catalytic converter was a non-issue from this portion of DDXing your problem, but you do make a good point. Although I've seen 2 sensors on 92-95 models as well as later. Most people get rid of that stuff by the time they get into modifications of that system anyway. I'm sure there are others that deal with SMOG/BAR/REF, or whatever, but I do appreciate that point of view.

motoxxxman

I'm thinking things started to heat up, timing pulled back a little, caused more heat, more retard, and just a cycle of this til it started glowing. my guess is the exhaust valves were also glowing and were causing preignition. and with severely retarded timing, and probably running rich too, viola, big power loss

TomCat39

Yeah, that's precisely what TheShodan explained happened with lugging the engine.

jdblock

Still wouldn't say the engine was "lugging".

Operating out of it's intended purpose, most likely. A restrictive exhaust, and a catalytic converter designed to heat up quickly for smog can cause a restriction that will choke airflow when parts heat up. If you can't get exhaust out, you can't get fresh air in. Results, loss of power.

I'd say there was a loss of VE, not the computer changing timing to a point where it would harm the engine. Engineers wouldn't design those perimeters into the ECU.

DCFIVER

An overly rich condition is essentially the main reason that can cause the manifolds to glow like that. A plugged exhaust CAN cause that condition as well,but typically would occur in the entire rpm range and not manifest itself after 20 mins of driving.


I wont bother to speculate as to why its running rich,but that is the most likely the root of your problem.....

(Ive never heard of "lugging" occuring in a feedback/computer timing controlled vehicle,even one as old as ealry 90s. I doubt that was the issue, though I dont have a counter theory other that the vehicle running rich.)



Also a catalytic converter can be completely plugged up and never set a code.....

holmesnmanny

Generally speaking, and usually, only obd2 Hondas have downstream oxygen sensors. Not really sure how you didn't know that. Perhaps you've never worked on an obd1 Honda before.

holmesnmanny

Cats have lots of internal gaps and holes inside of them. As they break down they will eventually break apart and clog up.

https://www.google.com/search?q=cata...w=1920&bih=950

TheShodan

iTrader: (14)

Happens plenty in both turbo and NA cars from 89-99. Doesn't have to be the computer being responsible. It's on engine load with timing.
Catalytic converters clogging? Only with shitty fuel.... And after being the same 26 year-old cat. Must be a California thing.

TheShodan

iTrader: (14)

I own 2 OBD2 and 1 OBD 1 Honda.. currently. I am the original owner of all three from 1995,1997, & 2000. Still own all 3 cars.

And yes, I've been wrong before.. But I doubt it on this one, based upon his symptoms.

holmesnmanny

https://www.google.com/search?q=cata...ter+clogged+up

holmesnmanny

Who cares who's right or wrong. I'm not saying I'm right. I threw out an idea of what COULD be the issue. What you do with that information is entirely up to you. I don't post here to outdo anyone. I post here to help anyone.

DCFIVER

Been repairing and diagnosing drivability problems for 20 years. Ive yet to run into it occurring "plenty" of times.

You could be right,it could be the issue, my experience says otherwise, guess we'll never know for sure.
Has very little to do with fuel. Or being in California, and happens quite often.


My point was,early in the thread you claimed that there would be a code before the cat would become clogged enough to cause a drivability problem. That was wrong.

In fact your whole understanding of how that particular system works is incorrect(based on what you have posted so far), but Im not here to correct that or bash you , Im merely trying to "guess" as to Tomcats problem.

TomCat39

If the cat had become partially clogged, would it not be problematic afterwords too and spawn it's ugly head periodically?

After that one instance, we never had an issue with the truck ever again until it was sold back to a dealership over a year later, problem free.