Re: Hesitation at middle RPM under moderate load

On Jul 22, 7:14 pm, Hachiroku ???? wrote:

What you describe is what happens when the intake valves get carboned up. The Techron was a good idea. It will clear that stuff up, but it takes a while. Course, it could be running lean due to other problems, but keep the possible carbon in mind. It's pretty common. What happens is the carbon snow cones behind the intake valves, and when under a heavy load, or when hot, the carbon will expand and keep the valves from fully closing. So you start losing compression. Remove the heavy load, and it starts running right again. The carbon also soaks fuel and can cause lean running. The only real way to tell if it's a fuel pressure problem is to actually hook a fuel pressure gauge to the engine. A car with a super carbonized engine will quit running once it gets hot enough. We had a Camry that had that problem. The dealer had it for two weeks and never could find the problem. They blamed it on the wiring harness, and charged us a load of money for not fixing the car. I ended up finding the problem myself, which was severe carbon. Anyway, like I say, it may be something altogether different. But keep the carbon in mind, cuz I've noticed most mechanics won't think of it. The Camry was in three different shops, the third being the dealer for two weeks. None of them could figure out the problem. It took me a bit of pondering before I found it. The first thing I did when I drug it back from the dealer was to check the wiring harness, which the dealer claimed was uncheckable. :( It took me about an hour to check every single wire in the harness. So much for uncheckable.. Never tell an extra class ham a wire is uncheckable..They will never believe it. I know I didn't. :/ I had to build a pressure gauge, and after checking the whole car out, could find no obvious problems. But it still wouldn't stay running once it warmed up. But I finally found the problem after noting the loss of compression when it did it. The starter would spin faster than usual, and often erratic due to the loss of compression in some cyl's, but not all. I ran a long hose for the fuel pressure gauge and was watching it as I drove. It was fine and never dropped from normal. If it's carbon, it will keep getting worse until the point on steep grades it will totally quit running after a while. Super bad, and it will quit running when it's hot, no matter what load you are putting on it. Keep running the Techron for a while. Two bottles worth will knock it out enough to tell if it's carbon or not. Maybe even one bottle if it's not too bad. Then again, I guess it could be an ignition problem.. :/ It's all a guessing game when you are on the interweb and can't see the malfunctioning machine.

It means something's not right.

Hachiroku $B%O%A%m%/(B wrote in news:4c48df07$0$74748$ snipped-for-privacy@read01.usenetall.se:

Got EGR? Checked that"?

I doubt if the problem is related to fuel delivery if the engine runs ok in lower gears and you can get it to rev.

I second the carbon buildup on the valves. Hook up a vacuum gauge, and when the problem is occurring, see if vacuum drops. If the Techron doesn't work, find a shop with Motor-Vac or that has a way to do the walnut shell blast.

As Tegger mentioned, the EGR is also a possibility, but not likely to cause the seemingly random other than heat symptoms you're describing.

Go ahead and try to prove that I'm wrong.

The original poster mentioned using high-test gasoline in it just because it was cheap right now.

If you run enough high-test in an engine designed with fairly low compression, you're apt to wind up with carbon deposits as a result.

--scott

Around here, any gas from a Gulf station would be at least 25 years old, and 93 octane would be leaded. Could that be your problem? ;)

In my extremely limited experience, I've seen only three cases where a fuel-injected vehicle hesitated: bad fuel pump, bad insulation in an ignition wire, and throttle position sensor developed a worn spot, and only the latter gave no symptoms at lower speeds. The fuel pump caused hesitation from idle, and the ignition wire caused occasional rough idle (arcing through, but the insulation showed no cracks or pinholes, even under a magnifying glass). A regular ohm or volt test didn't show anything wrong with the TPS, but when it was hooked up as a volume control, the sound was scratchy when the TPS was rotated around a certain area. Some people test by feeding it a signal through a resistor and looking at the waveform on an oscilloscope, and a worn resistor or wiper shows up as flashes of noise.

I read that cars with computer-controlled ignition may ping or hesitate at only certain speeds because the timing and dwell aren't adjusted smoothly with RPM and vacuum over their full ranges, as they are with older cars, but instead the computer may adjust them a lot over narrow ranges. IOW vacuum leaks can make the MAP sensor send the wrong information and prevent the computer from adjusting the ignition properly.

I'd start by misting the plug wires with the engine running and watch for a light show. Like someone said, it may be worth unplugging the egr valve and test driving... HTH, Ben

This YouTube video features wealthy Americans discussing carbon on the valves:

Good point. Use what the owner's manual says to use.

Over here, we only get one Petrol and that's about 95 RON. De-coking, or you might call it decarbonising is now very rare with today's modern fuels, 50 years ago a de-coke might have been performed ever 20k or so but with the detergents now in fuel a good blast down the motorway normally cleans out any muck that might have accumulated during light start stop, idling type of driving.

I have not run across valves with deposits in a long time - I suppose that the fuel additives actually work!

If the engine is designed to run on regular, but it runs better on the mid-grade now, that's another sign of heavy carbon buildup. The actual combustion area has become smaller because of the carbon packed on the piston.

I don't know how much good that stuff really does, but it won't hurt.

--scott

I wish there was an additive to make a catalytic converter stop burning money. My check engine light came on 6 weeks ago, due to error code P0420. Inspection doesn't come around until November, and there are no other symptoms, not even a change in mpg, so I'm putting off the repair until I feel delighted to spend the money. Ha. Meanwhile, as a tease, the light went off for a week, then on again.

On Jul 24, 11:07 am, snipped-for-privacy@panix.com (Scott Dorsey) wrote:

It works pretty well. Better than a lot of the other brands of stuff they sell as fuel treatments, etc.. One thing about Techron though.. It works best when the engine is shut off when hot and can sit and heat soak for a while. It does little when you are actually driving. It's when you cut off the engine and can let it sit that it melts the cheese. So the best way to clean out carbon with Techron is to do lots of run cycles over and over. IE: Run the engine until it's hot, cut it off and let it sit for an hour, and then repeat, over and over. That works a lot better than dumping a bottle in and burning it up on the highway in one shot. I believe Toyota actually recommends Techron for such a case vs other brands. I know when I had to clean out that Camry, I was shooting it directly into the intake, and could tell that Techron was working better than one of the lesser brands I was trying. I was using one of the cheaper brands at first trying to save some $$$.. But I found out that the extra for Techron is generally worth it. It does work better. It took me almost a week to get it all cleaned out of that Camry doing it the slow manual way.. It was really bad. But things sped up a good bit when I switched to Techron. If I were in a hurry, I'd go find a shop with a motovac machine. I'll usually dump a bottle of Techron in my car tank about once a year or so just to melt any cheese that builds up. The gas I buy has it, but you never know for sure if it's really enough... I'm sure the strength varies being as it's a packet added to gas at the terminals.

That's why I stick to top tier gas these days.. Supposedly, all gas sold is supposed to have a minimum amount of detergents. But I'm sure they vary, and the chemicals will vary. IE: Only Chevron and Texaco use Techron. Shell uses their own proprietary stuff along with hyping oxygen as a cleaner. Ditto for Exxon.. They use their own stuff. But if you buy gas at 7-11's etc, all bets are off as to what they use. Will depend on what brand they claim to be.. Some are basically "no-name"... So the last few years I use only the top tier gas to try to avoid the problem. For my Corolla, only Shell, Exxon, Chevron, or Texaco.. I don't use anything else in that car. Of those four, I probably use Exxon the least. But it seems OK. I use it on trips a good bit as that's the brand the particular stations I go to have. I probably use Chevron and Shell the most, but it depends what is handy.

In message , snipped-for-privacy@wt.net writes

Many moons ago, when cars had carburettors, it was not uncommon to take off the air filter, rev the engine and pour Red-Ex straight down the throat and watching until the black smoke goes white, then the internals were clean. Modern fuels seem to have done away with the practise.

In message , Hachiroku $B%O%A%m%/(B writes

That looks like an old Volvo 1800, is it?

I always used tranny fluid.. I still do that on my old trucks when I do tune up's or oil changes. Water can even work as far as knocking off carbon. But I always like the auto tranny fluid.. I think it soaks in a bit better to break up the stubborn carbon. Both my old Ford trucks use 6 cyl engines with Carter one barrels.. One is a 1968 F-250 with a 300, the other a 1974 F-100 with a 240. They get the tranny fluid carb blast every once in a while..