BanditWS6

Okay, this is a long shot, but a mechanic today told me that this could be possible, and I'm looking for some verification.

First of all: I have an '89 Formula 350 (L98) that runs poorly at low RPMs (1000-1300). It stumbles and sputters a lot, especially when you're at low throttle trying to go slow in a residential area. It also smells of gasoline and gets horrible mileage, so I think the ECM is enriching the mixture for some reason. My BLMs are in the 145-150 range all the time, indicating lean, so that would seem to suggest that the ECM would be trying to add fuel. I do not have a fuel press gauge, but I do not believe that there is a fuel delivery problem since the additional fuel is making it quite rich. (Not rich enough for any black smoke, but enough to smell it strongly.) I also have brand new 22# injectors, and this problem has been going on since before I installed them.

Here's the deal. A mechanic told me this morning that I might be having this problem because both of my dual catalytic converters were removed (by the previous owner). The lack of cats would somehow keep the air/fuel ratio from ever being optimal. I have not yet investigated what has happened to the AIR pump and tubes that used to run to the cats, but does anyone think this could have anything to do with my problem? I know that the target A/F ratio of 14.7 is set because that's what the converters like best, but I've not heard the argument that removing the cats will foul it up. Is that even possible, since they're downstream from all the sensors and such?

I have replaced the O2 sensor and it didn't help. I've checked the TPS and it is working correctly and seems to be properly adjusted.

Any ideas?

ede

don't think the cats, or lack of cats is the problem. is the tune up good, scanned for codes?

BanditWS6

Nope, no codes. Timing is good. Plugs look fine. Distributor cap and plug wires are new.

I think I'd be on to something if I could figure out why the BLMs are so high, but that's what's getting me.

five7kid

iTrader: (14)

This sticky on the Exhaust forum may relate to your issues. https://www.thirdgen.org/techbb2/sho...hreadid=213310

BanditWS6

Thanks five7kid, I am going to get out my Helm manual and see what I can learn about the AIR pump and its hose routing. Hey, the more I read of that sticky, the more interesting it gets.

I forgot to mention that the symptoms I'm having only occur when the car is warm. If I start it up stone cold and drive it, it's absolutely 100% perfect. I'm guessing that the problem is related to something that goes into effect or is monitored in closed loop. According to my DataMaster recording, that's right where my problems seem to start.

five7kid

iTrader: (14)

And the A.I.R./O2 interaction wouldn't be an issue until closed loop.

305sbc

iTrader: (3)

Noway. You need to find another mechanic.

Have you tried replacing the O2 yet?

bes217

He already said that he replaced it.

305sbc

iTrader: (3)

Time to scan and datalog

BanditWS6

I've already recorded a ten-minute datalog from DataMaster, but I want to take another one since I changed the O2 sensor and drive at a larger variety of speeds and such.

I'm still new to pretty much everything here and have been learning little-by-little about how to interpret what the ECM is telling me. I'm not certain what "normal" readings are for some of these values, but the ones I do understand seem to be normal. Only thing that stood out at me, as I mentioned, is that the BLMs are always high -- like between 145-152. They never peg at 160 though. BLMs go high the instant the engine starts.

Not getting any knock counts. INT keeps toggling back and forth between rich/lean (as I believe it is supposed to do, as this is normal reaction to the O2 sensor crossing over) but tends to spend more of its time on the enrichening side of the scale. I might be able to learn more if I knew how to interpret the change in the active fuel cell, but I still don't know anything about the fuel cells yet. Looking for info on that.

305sbc

iTrader: (3)

What is your O2 readings saying?
and what coolant temp are you running?

BanditWS6

O2 mVs are oscillating back and forth between 40ish and 900ish. Crossovers seem pretty regular. Based on what I know of how an O2 sensor works, it looks like normal operation to me.

It was a slightly chilly evening here (this is Florida, remember ) when I took the readings. Drove it for about 13 minutes and it took about 7 minutes for the coolant temp to get up to 150.4 F. Once it hit that value it climbed more slowly, eventually reaching 181 F as I sat in the driveway idling at the end of the trip. It was 9:16 PM and I'd say the ambient temp outside was somewhere around 55 degrees.

I began to wonder today if my fuel filter has been changed recently. Looking back through my records (from the previous owner) I don't see any indication of that. He changed the fuel pump due to a failure, but I got nothing on the filter. For a five dollar part, I'm sure going to get one this weekend and see if that helps any. What have I got to lose.

jdrafke

Kinda sounds like my problem. Does it run better once its warmed up? Mine stumbles bad and smells of gasoline too. This is until it warms up and it runs a bit better. Failed hc at emissions by about 1.20(alot).Changed everything plugs, wires, cap and rotor, o2 sensor, coolant sensor, checked tps voltage(.54). No codes! Let me know how the fuel filter went.

brent4a

What temp thermostat ?? Mine was all due to running a stat too cool and when changed to 180,it was fine.

jdrafke

any luck with the filter fixing ur prob?

83_1/2 L69

Do you have any exhaust leaks?
If there is a leak in the exhaust, air is pulled into the exhaust in-between pressure pulses. The O2 in this air confuses the computer into thinking it needs to add more fuel. Even a leak downstream of the sensor can work its way upstream to the sensor during “cruse” conditions.