Anybody here know cars? Specifically the drive train?

[cjsmith]

The car: 1989 Toyota Corolla, automatic, 119K miles on it.

The symptom: Momentary power loss, less than a second long, at intermittent and hard-to-predict intervals. For a while it seemed to happen mostly near speeds where the transmission should shift, but now it isn't doing that any more. Most recently it's happened in a fast cruise -- when driving on a highway for twenty minutes or so at 70MPH, the car started having these little power pauses, and they increased in frequency rapidly to the point where the ride felt almost like a rough road. I varied my speed in response to this, moving briskly between 65MPH and 75MPH, and it stopped. It seems to happen much more when the car is warmed up than when it is not. I don't know for sure whether it's the engine or the transmission. I am guessing that it isn't something obvious, though, because this symptom has persisted through one visit to a well-recommended shop.

The question: What are ALL the things this could be, including some off-the-wall ones if they're possible, and how can I narrow it down a bit with some tests and inspections?

I don't have good jacks, nor do I have an engine tachometer. I can think of a good use for an external engine tachometer right away, but I don't have one handy. :-(

Comments

[deyo.livejournal.com]

A common cause is a sticky electrical or belt-driven component. An electric motor puts a tremendous strain on the alternator at low RPM, and if it spends too much time there, you'll actually notice the alternator dragging the engine. Similarly, if a belt spindle (like the A/C) engages but has to be jolted out of zero speed, the jolt comes from the engine, and is delivered straight to you! ;)

The fan is the most likely culprit, since it is the one component that reliably switches on and off (dependant on moment temperature), whether it is belt-driven or electric.

[cjsmith.livejournal.com]

I wish wish wish I could figure out whether it was really engine power problems or transmission trouble! Durn not having a tach, anyway. OK, I can check some electrical and belt-driven components (briefly, anyway) by disabling them...

Can discount the A/C, at least; have seen this happen without using A/C.

Thanks for the brainstorming!

[wcg.livejournal.com]

Trying to identify the full set of possibilities is tricky. I'll mention right now that during my time as a line mechanic, I never liked to attempt long distance diagnosis, because it's a recipe for frustration. That said...

If the car is losing power, you have one of these happening:

-- Loss of fuel. This could be due to a failing fuel pump, a worn pressure line inside of your gas tank which is intermittently bleeding fuel back into the gas tank and then resealing, an intermittent fuel leak at a connector under your car (do you ever smell gasoline?), or an onboard computer problem which results in the injectors not providing sufficient fuel.

-- Loss of spark. This could be due to a failing magnetic pickup, a failing electronic ignition module, a failing coil, one or more sparkplugs going bad, one or more plug wires arcing to ground or each other, or an onboard computer problem which causes the timing to retard for some reason.

-- Restricted exhaust path. An intermittent problem like this could be symptomatic of partial clogging in your catalytic converter.

-- Combustion mixture poisoning. This is generally caused by a sticky EGR (exhaust gas recirculation) valve which gets stuck and allows too much exhaust gas to mix in with the intake stream. It can also happen if one of your engine sensors is going bad, giving a false reading to the onboard computer, which then tries to "correct" the pseudo-problem by adding exhaust to the mix and/or retarding the timing.

Given that it's an intermittent problem which has already flummoxed some good mechanics, I'd look at some of the stranger fuel supply problems. Those don't generally reveal themselves in diagnostic codes. If I were troubleshooting the problem, I'd test fuel rail pressure, check the undercar fuel lines for leaks, and if I didn't find any external leaks I'd drop the gas tank and check the submersible pump inside there for line failures. A pinhole leak in one of those inside the tank lines would be a plausible cause of the problem you describe.

I wish I could give you a more narrowed answer, but honestly I can't.

[cjsmith.livejournal.com]

long distance diagnosis... a recipe for frustration

I hear ya. Some people seem to thrive on it, but I'd probably go nuts myself.

All your suggestions seem to be focused on the engine itself losing power; I'm intrigued that you seem to discard immediately the transmission. I like that; it could be good for my wallet :-)

Fuel line leaks sounds like something I can begin to check as soon as it's light out. I haven't smelled gasoline, but now I'll be looking for it.

Loss of spark is intriguing too; the symptoms are soooort ooooof like the ones I had when my distributor wiring harness had gone flaky and one or more cylinders were either misfiring or not firing at all. No backfires, though, with this symptom set, while the distributor wiring problem gave me some of those.

Not sure how varying my speed would make the problem go away if it were a partial blockage somewhere in the exhaust system. (On Monday night's drive, once the problem started, the only time it went away was during speed variation. Gah, that was tough, paying attention to the road and keeping continuous changes in speed going, when I was very very tired. Then Tuesday, after the car had sat around a while, it was behaving nicely again.) Will noodle more on that.

Mucho thanks for the brainstorming!

[sinboy.livejournal.com]

Oops. Gotta keep track of who's logged in here.

As I was saying...

Check the vaccum pumps and seals. We had a problem with our Tercel (same year) loosing power at odd times and stuttering. It also might be the carburator, if yours has one.

carburetors

[shadopanther.livejournal.com]

If she has the 4-AF engine just like mine does, then it has a carburetor. Off the top of my head, I'm not sure when Toyota switched engines (I'd have to check my repair manual). However, the earlier 1989 Toyota Corollas like mine (manufactured November 1988) are carburetred.

-- Shadopanther

Re: carburetors

[cjsmith.livejournal.com]

Yep, I'm carbureted. I can check the throttle valve, that'd be a good start... if it's sticky, or something, I can imagine why varying my speed might have an effect.

Thanks!

Re: carburetors

[sinboy.livejournal.com]

Well, short of driving in the car when it happens, that, based on my experience with my Toyota, would be my guess. Or the vac seals/pumps. Those go out really easily, and create an intermittant problem.

[cjsmith.livejournal.com]

Thanks for the idea! My repair manual suggested a test I could do, the results of which might point to vacuum trouble, but maybe I'll just jump to the section on vacuum stuff and see if I can at least check for seal damage.

Try Car Talk

[cwilson.livejournal.com]

You might want to try posting your problem to the Car Talk
discussion boards:

http://www.cartalk.org/board/

It's the web site for the Car Talk radio show, and they have very
active boards where people post problems they're having with their
cars. The replies seem to range from people who have no idea what
they're really talking about to people who really know a lot about
cars or who claim to have had the same thing happen to them. You
may not get useful information, but it's free and easy to do, so
it might be worth a shot.

You can also search the board archives for your make and model and
see if anyone else has posted a similar problem.

Good luck!

Re: Try Car Talk

[cjsmith.livejournal.com]

Thanks for the idea! I admit I'm a little reluctant to display my complete and total ignorance in front of a bunch of people whose toolboxes are worth more than any car I'll ever own, but hrm, maybe it wouldn't be quite as humiliating as I imagine... and it just might help...

1989 Toyota Corolla

[shadopanther.livejournal.com]

Momentary power loss, less than a second long, at intermittent and hard-to-predict intervals.

That reminds me of a problem I had with my 1989 Toyota Corolla a while back, only I seem to recall my momentary power drop outs occurred more at lower speeds. As it was intermittent, it took a second (maybe third) trip to the shop where I had one of the mechanics (or service people) take it for a test drive with me -- and, fortunately for me, the problem did reoccur on the test drive & therefore gave the mechanic a clearer idea of what to look for.

Checking my notes, I have not found anything that looks specifically like that problem that I am remembering -- but I have found that I have had the alternator and spark plugs replaced. (Not that it means anything in your case -- even with the same model & year of car). Also -- I don't happen to have an external tach, but I do have ramps & a Chilton Toyota Corolla 1988-97 Repair Manual. (It's a new manual since I lost my old one.)

If I find anything else, I'll let you know.

-- Shadopanther

Re: 1989 Toyota Corolla

[cjsmith.livejournal.com]

Thanks! Yeah, my alternator's been replaced too (my car eats alternators) but this isn't similar to that set of symptoms. Distributor wiring harness is closer, symptom-wise, but that's fairly new, too... I guess it wouldn't hurt to think up some way of checking that. Spark plugs may very well be ancient; that's a good thought. If I'm just not firing much on one cylinder, that'd do it, especially if the engine is running hot and that cylinder sometimes self-ignites with an off timing.

I have the 1989 Corolla repair manual if you ever want to borrow that. 8-) Unfortunately it really wants me to have some equipment I don't have. No surprise there!

[joedecker.livejournal.com]

Knowing less about these things than wcg and some of the other folks, I''m hesistant to offer up too much,
but it does remind me of vapor lock in some ways, which is another form of fuel problem. Bill's suggestions in that vein sound more likely, but a key hint to vapor lock would be the symptoms never happening in the first few minutes after starting the car from a point where it's dead cold. Vapor lock comes from (if I recall correctly), fuel vaporizing in the fuel lines, the bubbles causing the power losses. But being a software guy, you should take my memories with more than one grain of salt. :)

[lkeele.livejournal.com]

Rondo says:

You've been given lots of advice, and some of it is pretty good, in particular fuel or electrical problems. The fact that the cut-out is associated with shift suggests that vaccuum-actuated devices associated with the RPM of the motor are failing to work.

Could be:

--Vaccuum advance on the distributor (assuming you have a distributor, not electronic ignition).
--Various vaccuum-actuated devices on the carburetor.

I would say also, don't discount the beginning of some kind of fuel pump failure. It is difficult for me to imagine it being something with the transmission.