mystery intermitant power loss over 40 mph ?

[jberger62]

I did a tune up on my '91 Festiva w/manual tranny (165,000mi) yesterday in hopes of getting rid of this "flat spot" problem I've been noticing throughout this past year.
I installed:
New plugs,New wires, New Cap & Rotor, PCV, Oil/filter Change,Air & Fuel filters...
all to no avail :shock:
I also changed the O2 sensor about 4 months ago.
Here's the deal:
The engine starts,warms-up and runs just fine until it gets to around 40-45mph (or higher highway speeds)and that's where the problem rears it's ugly head and the check engine light makes it's presence known.

When the check engine light is on it feels as though the engine is temporarily being robbed of power.

Once I take remove and replace my foot on the gas pedal; the check engine light goes out.
Does this sound like anything that's happened to anyone on this board before?

I don't see any "codes" being flashed, so i am baffled here.
Please help me to figure this crazy thing out.

I read this in another thread on here and am planning on trying this when I get home today.

FestivaBiker1971 said:
OK, here's how to run a QuickTest (code retreival). This should be the same for all EFI Festies. The setup begins with the key off. Also turn off all accessories (radio, a/c, lights, heater).

Find the two test connectors. They are both to the outside (driver's) of the master cylinder. One will be a single pin connector with a yellow/green wire, and the other is a 6 pin with three wires; yel/wht, yel/blk, blu/grn. Get an analog voltmeter, set to a range between 12 and 20 volts, and connect the black lead to battery ground. Connect the red lead to the yel/wht wire (SelfTestOut). Use a jumper wire to connect the single yel/grn wire (SelfTestIn) to ground. You are now ready to test.

Key On Engine Off Test (KOEO)
Turn the key on and watch the meter. The code can be a single or double digit, depending on the fault. Watch and count the meter sweeps. Its not important to watch the meter immediately, the codes repeat as long as STI is grounded. There will be a short pause between digits if the code is double digit, then a long pause between codes. There will only be long pauses between single digit codes. Short pause is about 2sec, long pause is about 4sec. Pulses are 1.6sec long. A reading of sweep-sweep-long pause-sweep-sweep- long pause is a repeating code 2. There is no code 22 to prevent confusion. A reading of sweep-short pause-sweep-sweep-long pause-sweep-short pause-sweep-sweep is a repeating code 12. After about 1990, MECS (MazdaEngineControlSystem) added a 'zero' before the single digit codes, represented by 10 sweeps.

Key On Engine Running Test (KOER)
Disconnect the STI wire from ground, then start and run the engine till warm. Since your concern seems to happen cold, try it cold, but understand you may get an unwarranted coolant temp code. After the engine is running and warm, ground the STI wire, shut engine off then restart. Momentarily disconnect then reconnect the STI wire to ground. ECU should now output any running codes.

Post what codes you get, and I'll give you a breakdown. This info is also available in the Haynes and Chilton manuals.

[Krankendil]

exhaust back pressure

I wonder if it could be that your catylitic converter is getting clogged up and at higher speeds is causing back pressure to bog down the engine. That was the problem I had once with a Bronco.

Krankendil (Dayton, Ohio)

[jberger62]

I replaced my entire exhaust system last year with all brand new components...including a brand new Catalytic Converter.
I wouldn't think it's clogging already.

[nonamekid]

Does it happen with a certain rpm range in different gears or is it directly related to speed? Can you accelerate past 50 in third gear?

The code retrieval will only work when the service engine light is on.

[jberger62]

The code retrieval will only work when the service engine light is on.

So then I'm not going to be getting any codes that'd tell me what's happening
I guess that'd be too easy huh :roll:

The prob usually happens in either 4th or 5th at, as I've previously stated, around 40 mph and above.
I'm not too sure what the rpm is when it happens due to the no tach dash I've got in it.
Accelerate past 50 in third?
I honestly don't think I've ever tried before. I usually shift into 5th at around 45mph so I can't imagine 3rd @ 50.
Anyhow, what does the 3rd gear 50mph acceleration test show us?
Thanks for your input and help everyone, I appreciate your help with this.

[FB71]

dude, Uncle Fester is a 4spd carbed car, and I don't shift from 3rd to 4th till 65mph.....

[jberger62]

O.K. ,O.k., so I took 'er out this morning and thrashed the crap out of 'er.
Thrashed I'm most certain mean different things to different folks.
I personally don't get off on beating the snot out of my only means of reliable daily transportation.

Yes, I got it up to 55+ in 3rd gear before slamming it into 4th...flooring the accelerate and waiting 'til around 65 to slap it into 5th and take it up to a casual 75+ mph before running outa road.
After a couple of 55mph+ rips down the road in third, it seems to have diminished the prob...but not eliminated it.

[rotinaj13]

yep clean that carbon out! lol I do it frequently! lol I accidently cleaned the carbon out of my tranny to and the spider gear fell apart ;-)

[jberger62]

Well, it (the check engine light) hasn't come back on since the high rpm carbon cleaning that took place this afternoon.
It does idle a lot rougher now though when the engine is still cold...almost conking out at one point :shock:
I thought about adjusting the dash-pot at one point and raising the idle rpm a scosche but after the engine was warmed up it ran fine.
I guess I've just gotta let it warm up a bit longer before hopping in and driving away huh.
A friend of mine a while back poured about a dixiecup full of water
(a little at a time) down the throat of my Blazer's carb (after the engine was fully warmed up) when it was running like crap.
He'd pour a little down, then rev the engine a few times.
The process (pour and rev) would go on until the cup of water was empty.
He said it was like steam cleaning the inside of my engine.
It did actually seem to run a lot better after those steam cleaning sessions.
I'm wondering if spraying (with a plant mister) some water into the throttle body while revving the engine would have the same effect or not???
Whatdoyathink :?

[FB71]

Here's what I've done for carboned-up top ends...

First, mix about a quart (total) of 3 parts water, one part tranny fluid (atf). Make sure the wateris hot, boiling if the containere will tolerate it. Shake it up into a pink milkshake. You'll have to shake it every minute or so. Get the engine up to temp, pull off a relatively small vacuum line (like NOT the brake booster), stick it into the mixture while holding the engine at about 2k rpm. Its gonna smoke like a freight train.... When the mix is gone, shut down the engine and let it cool. After its cooled down for an hour or two, take it out and run the piss outta it. You'll be suprised, I think....

[rotinaj13]

would that work for stuck rings? I got horrible blow by and I don't think it is due to damage.... carbon SUX!

[FB71]

doesn't work for stuck rings. Check w/ darkdan, he knows of some stuff he says works really well for that. He posted it about a month ago.

[rotinaj13]

doing a piston soak with seafoam, then using the auto-rx oil treat ment lol I all ready talked to him, was just curious what the limitaions were to the "milkshake" lol :wink:

[jeffdjeffd]

I've done Jim's trick, although I poured it right down the carb. It's a fairly common hot-rodder trick. Lots of smoke. Lots.

[jberger62]

So do you think it'd work with a throttle body?

Spraying/pouring water into the throttle-body throat?
I mean i know it works with carbed vehicles, but what about EFI vehicles?
I'd really rather not f%3@ things up by spraying water ( a little at a time) into my throttle body, revving the crap outa the engine and repeating the process several times while steam-cleaning the underside of the manifold.
Has anyone here done that before?
I'm happy to find someone else who knows what the heck I am referring to with the water (steam-cleaning) trick.