Well, I've been reading this forum for about a month now, finally signed up for an account. I've just started into prom programming, and I built a aldl interface to do some datalogging as well. My car had been throwing a code 45 (rich mixture) whenever I was doing extended highway driving, and I was determined to figure out what was causing that. Looking at the oxygen sensor graph in TunerPro, I could see that the voltage fluctuation was very sporadic, and while cruising on the highway, the sensor would occasionally stop cross counting and hang up at around 900mV, thus throwing the code 45. In most all blocks, my BLM was 108; only during some (non-PE) accelerations did it ever rise, but never anywhere even close to 128. I pulled the plugs, and every one looked a bit lean. I had always thought that O2 sensors tended to fail lean, but I couldn't think of any cause other than a bad sensor. Intending to go wideband in the near future, I bought a cheap bosch to hold me over until then.

And now here I am. The bosch is giving me the same rich readings. Now I know these sensors suck, but both it and my previous sensor are in agreement with each other, and even my tailgating cousin tells me I smell rich. I increased my injector constant, and started getting BLM's around 110 while idling around in block 4, but when I pulled the plugs again they just looked too lean to risk pushing that any further. Now, I don't know a whole lot about plug reading, but I'd be much more comfortable seeing tan tips than gray tips, and as far as I'm concerned the plugs don't lie.

Here's a snapshop of what typical 70mph highway cruising looks like in my logs, and a picture of the number 3 plug. This is with the stock chip and a BLM of 108, and the ECM throwing a code 45 (rich). Taking more fuel out, the whole tip turns gray. The plugs have 300-500 miles on them. Anyone got any ideas?

 

Skip everything u are trying to do first.

Make sure the car is in good shape in regards to the plus/wires/cap/rotor. (I would assume u have investigated all of theses am I correct)

Second is the car stock or modified already? And if so what modifications are present.

Third, if it is stock or modified, DO NOT LIE to the ecm and fudge the injector constant to make it run right. U can do this to test something, but I would do no diagnostics this way. Set the fuel pressure to 43.5psi and use the correct IC for the injectors in use.

If your running that rich you have major problems or a large cam :-)

What readings do u get from the coolant temp sensor? Does it jive with the IAT when the car is cold? U can test it warm as well with a scanner/datalog or ohm meter as well.

Leaking injectors can cause the same thing, might want to ohm them out and see what u get. anything remotely questionable I would pull the rail and check for leakage.

Leaking fuel pressure regulators will make it rich as well or a plugged return line. Check everything out.

Kinda hard to tell u where to look when we have so many unknonws about your car.

later
Jeremy

 

Hi Jeremy,

The engine's stock, the only real modifications I've made is a freer running exhaust. I recently had some fuel pressure issues (leaking pump-to-fuel line hose in the gas tank), but as a result I've already replaced the fuel filter and in-tank strainer, done a flow check and checked the return line for blockages, and verified I am now running around 42 psi no vacuum.

All my sensors seem to be in order, including coolant temp and MAT, nothing in the datalogs seems to show I'm getting bad data. I hooked the O2 sensor up to a scope and it seemed to be behaving exactly like the ECM shows it does.

I suspected a leaking injector, however I've pulled every plug and they all look the same. I'll check them with a meter tonight and see what I get.

I've also been through the ignition system, all the wires look good, got a brand new cap and rotor, plugs as I said are nearly brand new and properly gapped. Still no deal.

This is a high mileage engine, with some leaky valve seals. However I burn very little oil, and except for a little smoke on startup after it's been sitting for a few days, it runs very clean.

I do have plenty of logs available if anyone's curious too see if I might have missed something, like I said I'm still pretty new to this.

Thanks for the help,
Bryan

 

So the injector constant is set correctly for your fuel pressure and injector rating?

 

Yeah, I'm running stock 19lb injectors, stock memcal, and stock fuel pressure. Since the ECM is pulling all the fuel it dares out of the stock tables, and the plugs themselves look correspondingly lean, maybe I should force it into open loop and see what the plugs look like without any fuel correction.

 

I know this sounds weird, but i had a bosch oxygen sensor that would go ape when the car would go rich. The plugs seemed lean and the oxygen sensor said rich. On top of that i also had a leaking injector. Something for you to think about. I must say, i went to rehab and have not had a bosch sensor since.

 

So you're saying the plugs looked lean but you were in fact running rich? Or the leaky injector was throwing the sensor and leaning everything else out?

Looks like I'll be buying a new sensor sooner than I thought, anyone know where to get a real A/C Delco? I read elsewhere in the forums that GMParts was selling A/Cs that turned out to be Boschs.

Bryan

 

The leaky injector is what i believe helped my 02 on it's way out. It more or less ended up flooding the cylinder with gas.

 

GM claims that running rich won't permanently ruin an O2, but could temporarily numb its sensitivity, so to speak. The fix is to essentially increase your exhaust gas volume and temp (you can figure out how to do that).

I'm not sure which is more laughable, to be honest. That Bosch O2 sensors, time and time again, prove to function inadequately or downright wrong in GM cars. Or that people continue to buy them, try them, and argue for their use.

 

I've also heard from Holley Tech Support's "leading tuning guru" tha running very rich will cool down an O2 sensor to the point it thinks everything is very lean and hence pull fuel out to create a lean condition. However, that would only be temporary of the injector is any good 'cause as soon as it leaned things out it would "warm up" again and add the fuel back in. Do all the plugs look like the one above? If there is a possibility of a leaking injector you need to compare all 8 side by side.

 

Unless it's a lean misfire. But if that were the case, I think the driver would notice, back off the gas, and regroup.

 

Well, just to update. I really was running rich. When I filled up my tank, I did a few quick calculations and estimated I was getting around *13* mpg. I had just fixed a long-standing fuel pressure problem, and I think that once I had some actual *pressure* in the system, the current problem surfaced. I was checking the plugs before but never even thought to check the exhaust.. wet and sooty. I checked my injectors with a multimeter, one read 13 ohms and one read 8. Pulled the intake and fuel rail, pressurized the system and didn't find any leaks. Why the plugs look lean and how low-ohm injectors could flow more fuel, I don't know. Perhaps the pintles are gummed up and acting sluggish? That's the only explanation I can think of.. there's no other route for fuel to get into the engine. They're the original injectors on my 210,000 mile engine, I don't think ordering new ones is going to be a waste of money by a long shot. Hopefully the new set should get here before the end of the week.

-Bryan

 

Your injectors are bad and need to be replaced. This low ohm readings are a typical failure mode for the Multec's you have in the '91.

Try to find some Bosch injectors in decent condition that match the fllow rating.

RBob.

 

What the man said(rbob)and the same thing I recommended earlier to u, is whats causing a large part of your problems.

Anything below 12 is considered junk in the GM manual. I question even that much as I have seen failures start with just a couple ohms difference between injectors. (again this is only the electrical winding part of it)

Start there and see what happens after u have a fresh or reconditioned and tested set of injectors.

later
Jeremy

 

I ordered a set of Boschs last Sunday, hopefully they'll be in soon and I can get started again.

Thanks for the help,
Bryan

 

Not at all...With numbers that low, they were probably really close to frying the ECM.

 

Final update. New injectors are working great, been tuning and got my BLM's nearly rock steady now.

Thanks for all the help,
Bryan