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Discussion Starter · #1 ·
1995 LX

The car is my pizza delivery beater but I still love it. Gets me from point A to point B with great gas mileage while still looking good.

Lately, it's been pinging a bit under heavy (not full) throttle, and bucking once in a while at wide-open throttle when I'm under 2,000 RPM or so.

Got a CEL last week and scanned it

172 - Lack of O2 sensor switches - possible lean burn
186 - Injector pulsewidth longer than expected

So I figured with 112,000 miles, might be time for a new O2 Sensor.

Replaced that, nothing changed. So I went back and bought an Air/Fuel guage. I've been meaning to pick one up soon, but never got around to it.

Sure enough, at idle, she doesn't even register on the guage. driving, it "swings" to the bottom of stoich and then back off the lean side of the guage, and at WOT above 3,000 RPM or so, it locks into stoich.

It SHOULD be locking over to rich, but it's not. And when I'm idling after the car's warm, it should swing from lean to rich, right? It shouldn't usually fall off the lean end of the meter!

I checked my O2 sensor connections, cleaned them, cleaned the MAFS sensor, checked my vac hoses... I'm at a loss.

Any ideas?
 

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Are you using a wideband A/F gauge? Those cheapo pod-type ones aren't very accurate.

What is your fuel pressure at wot?
 

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Discussion Starter · #6 ·
The guage is an AutoMeter Sport-Comp. For what it's worth, I also used an analog voltmeter all day 2 days ago while delivering pizza. It read 0-5 Volts.

I don't have a fuel pressure tester, and after ditching $130 on the guage, pod, and new HO2S, I am not buying one for at least another month :(


I'll pull the hose off the regulator though and see if it helps.

I, too, thought it was unmetered air, but once I hit 3,000 RPM's the car's whole attitute changes. Before 3,000 the guage swings off the lean end and it swings even at WOT. Once I hit 3,000 or so the car feels more alive and the guage stays in Stoich. I did notice that last night for a while, I was lighting up half of stoich and it was actually going over to Rich for a while. This happened after I cleaned my MAFS with a quick-drying electronic parts cleaner that was recommended to me by the guys at FocusSport when my Focus's MAFS went bad.

The vaccuum check was only visual. I did pull a hose off the manifold last night. It almost killed my car :) However, I didn't actually use a vac guage. I don't know how to test my vaccuum accessories, but I'd assume I pull the hose off the manifold and use one of those hand pumps with the guage, to check each hose and the actuator it affects, ensuring it maintains a good level of vaccuum even after you stop pumping? That's how I'd do it I guess. I've seen vaccuum testers at the parts store, just never used one.

I pulled the whole intake tube off. It is free of crack and leaks, and from everything I can see, it's securely and properly attached to the intake manifold and to the MAFS housing.

Thanks for your help so far. I wasn't expecting this many replies!
 

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NOS, you need NOS, or a landau top... either one should solve your problem, j/k
 

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Could be the head gasket or coil pack. Mine did that when the coil pack was bad and when I was losing the head gasket. :cry: Oh well, I'm SPI powerd now! 8)
 

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I had the same issue w/ my 97.. Replaced all vac lines (6 bux) and left the ECU umplugged... no problems and it has been over 3K daily driven miles.
 

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datafive0 said:
I had the same issue w/ my 97.. Replaced all vac lines (6 bux) and left the ECU umplugged... no problems and it has been over 3K daily driven miles.
:?: and it still runs :?: you sure the ecu is what you unplugged?
 

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uhhh, if you unplugged the ecu, your shizzle wouldn't run, period... I'm not sure it would even turn over, or make that annoying dinging sound when you opened the door.... *runs outside to unplug the ecu, out of curiosity* :D
 

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To let it purge the error codes... discconnected the battery, change the vac lines and reconnect the battery...

Come on people, a little common goes a long way... Sorry if I gave too much credit :oops: :D j/k.. you guys are ok in my book, I did write it a bit cryptic..
 

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Discussion Starter · #18 ·
yah, I've reset the PCM before...

Anyhow, I also hooked up a vaccuum meter, and at idle, it's about 15-19PSI. I don't have a vaccuum pump to go testing lines with yet (I'm very broke)

For some reason, it seems to have settled down on the bucking. It still does it, but not as frequently. Maybe I just got a bad batch of fuel?
 

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Discussion Starter · #19 ·
okay... is there something magical that happens with the engine or PCM at 3,000 RPM?

It's still doing this occasionally, and also once in a while, it gets REALLY bogged down, for instance redlining 2nd and shifting to 3rd and going WOT, it feels more like I shifted to 5th for a moment, like 3 seconds or so.

The stumble or "bucking" only happens below 3,000 RPM, and oddly enough, at WOT, my A/F meter always floats lean to medium stoich. until 3,000 then right at 3,000 it darts over to full-on rich without fluctuating at all. If I back off the throttle, it will go back to swaying in the stoich, but above 3,000 RPM at WOT it's always rich.

Now, I know that cheap narrow A/F guages and O2 Sensors like mine are not any measure of precision, but if it's darting around and then goes full lean (as in off the scale, no LED's!) or full rich (only the lowest ratio LED lit up) you can pretty much guarantee that you've got a ballpark estimate of what's going on with your ratio.

Anyone have some clues? I find the RPM phenomenon kind of disturbing. is there something the injectors or fuel pump are told to do (like go from 70% to 100% duty cycle?) at 3,000? This is starting to look like a problem with my PCM or my fuel system.

EDIT: By the way, since putting a new O2 Sensor in and clearing my codes (what's that like a month or two?) my CEL hasn't come back on.
 

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Actually, I do have a bit of info on the 3000rpm phenomenon. Basically it's the crossover point where the ECU is set to go full rich for acceleration purposes. I stumbled upon this while cruising I-5 and hitting 3000rpm in 5th. I myself was rather currious why it suddenly went rich from a lean cruise mode. So I played with it several times and got the same results everytime I crossed the 3000rpm mark. It's normal so don't worry about it.

As to the floating, that is also normal below 3000rpm and until the ECU settles in a lean cruise mode. I.E. after you are done accelerating and traveling above 50mph.

Your full lean, off the scale, I would assume is when you are decelerating. Once again this is normal so don't worry about it. The time to worry would be if it did that while you were cruising or under acceleration.

And lastly, the 3 second delay on your shift is probably a dirty or faulty MAF. Normally you won't have that happen unless you suddenly downshift in lean cruise mode. The ECU is just a little slow to figure out you want to go so there is a delay before it actually adds gas.


Hope that helps a little. If you haven't changed the coil pack, I would start there. Or if you have an Accel coil pack, get an MSD or switch back to the stocker because that's exactly what happened when my Accel pack went.
 
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