I have written about this problem like 4 times and got no real answers, so I will make this short and sweet cuz Im tired of typing all this over and over.

Car runs good overall, has a small amount of search at idle, but not much, but major problem is in the way the car pulls. It just doest feel right, and i put an a/f guage on it, and at anything less than "power enrichment" or just short of full throttle, the a/f guage goes from okay to off the chart lean very rythmically and you can just feel/ hear it in the engine. I have replaced almost all sensors, injectors were all cleaned and flow tested individually, and the car seems to be fine at full throttle, guage stays perfectly steady in the rich zone.

please help me out, for some reason the computer just cycles from real lean to stoich over and over about once every two seconds at idle and any amount of throttle except full, you can really hear the motor change sounds following the guage on decel.

give me a direction!!

 

First of all, to really make one of those a/f guages work well, you need a wideband oxygen sensor. Your stock 02 sensor isn't very accurate and its supposed to give the computer a rich/lean flag relative to a stoich mixture (14.7:1), and thats about it. If you ever hook up a scan tool to your ecm you will notice that in closed loop the voltage will all over the place, crossing over between both extremes hundreds of times a second (they're called 02 crosscounts), which to the computer might be useful for acheiving stoich part throttle mixtures but it won't translate to a coherent reading on your guage. Thats why the computer ignores the oxygen sensor at WOT because it won't be able to accurately "tell" the computer that the mixture is the desired 12.5:1. Sure, at WOT the guage will read solidly rich at that point but its not going to show you "how" rich. I hope that made some kind of sense. now, have you done the little things like check for vacuum leaks, set the timing, or check the fuel pressure? If you haven't already done so, it might be a good time to get your hands on a scan tool and get data directly from the computer itself to check for any abnormal readings. Just because the computer doesn't throw a code doesn't mean nothing's wrong.....

 

As redfirebird said, O2 sensor data jumps around during part-throttle conditions by design. You only get worried if it reports constantly <450mV or >450mV. At WOT it should go into the rich area and stay there...890-910mV is the sweet spot for most engines. From your post, it sounds like your engine is behaving correctly.

Best next step is to get a scantool or rig up a laptop so you can read/capture ALDL data and see what the engine's doing. This is covered in the DIY-PROM forum article by TRAXION I believe, if not do a search on 'MOATES' and you'll get info.

Based on recent experience, I'd also check for ignition leaks. Mine had a slight stumble which I couldn't track down even with gobs of ALDL data, turned out to be a failed plug wire. Best time to check is at night, start up the engine and look for sparks.

 

Well, as I explained in previous posts, I have had an odd issue with timing where I think my balancer may have slipped on its rubber ring or something. I am using the stock "straight up" balancer along with the correct tab at the center of the timing cover, well this thing just will NOT run at 6 degrees on the pointer. It pings and runs horrible and idles up and down and stalls, the only way it will run is with the timing about an inch below the timing pointer. My only explanation is that the balancer outer ring must have slipped. After much playing it has the amount of timing it runs best with.

The car makes a solid 19" of vacuum at idle and I have checked all vac connections tons of times.

Back to the a/f guage though, the engine follows it up and down is my problem. At idle, you can hear the engine change as the guage changes, lean, then back up and the engine follows. It does the same thing all the time except WOT. It just pulls real unevenly at acceleration from stop. I have the fuel pressure set at 48-9 psi at idle.

I have had the car on a snap-on scanner and it doesnt really show anything wrong. I have an egr code because i have blocked it off and blocked off the vacuum to it. Otherwise all is good, as mentioned before I had all injectors cleaned.

Something is just telling the car to go rich and then lean back and forth. Anyone question the ECM???

 

Replace your balancer, get the timing set right, and start from there. If the outer ring has slipped, you're at risk of tossing it and trashing your engine.

You'll never get it running right with inaccurate initial spark advance. If you're running a stock chip, it wants 6deg BTDC and will run like crap if you're very far away from that.

 

Also could be a slipped chain. But you won't know till you get balancer problem fixed.

 

engines just turned 1000 miles yesterday, so I hope the chain hasnt slipped yet

 

TTT, any ideas???

it seems to run better at open loop

 

I'm in 100% agreement with this. You already know you have some stuff wrong, and you already know that these things could be causing your problems. It's time to quit thinking and start fixing. Fix what you know is wrong, then if the problem is still there, re-post!

And quit using the silly air fuel ratio gauge with the stock o2 sensor. the output is meaningless.

 

Well, you didn't seem to absorb any of what I posted earlier so I'm not wasting any more time on ya...seems like you're waiting for someone to fix it over the Internet for you.

 

If you're really in a hurry, you can find TDC and re-check the mark on the balancer outer ring. You could also install a self-adhesive timing tape, but you'll still need to verify the correct TDC.

Once that's confirmed, you can do some heavy-duty diagnosis.

 

the problem I have is fuel related.

I replaced the balancer yesterday with the correct one, and guess what....my timing is DEAD ON at 6 degrees. I did not have to move the diostributor at all. It is not a timing issue, I knew I had it very close.

Any other ideas?

I am considering a vacuum leak, but not anywhere obvious, I have done everything I can to locate one and found nothing.

 

ttt, someone has to have some ideas

 

Are you unplugging the advance wire when you check/set the timing? If not, your timing is probably way off.

you say your injectors have been cleaned recently. do you have a different set of injectors to try, just in case one of them isn't working properly?

Is the engine missing?

how do the plugs look?

have you pulled a compression check?

be more descriptive of the problem

 

yes the EST base wire is unplugged when Im setting the timing.

injectors were cleaned and pressure tested individually out of the engine, all were matched and tested and are basically a new set.

engine isnt really missing with the exception of what I feel is a slightly rough idle

plugs look good, but possibly lean

have not done a compression test but assume(yes, assume) all is fine since engine is all new.

problem is just the fact that the engine goes back and forth from lean to stoich area and you can feel/ hear the engine rpm/noise change as the ecm richens and leans, richens and leans over and over. At WOT, it seems to clear up which makes it seem like a closed loop problem, that goes away when its in power enrichment mode.

 

Cool you replaced the balancer, if the old one had failed you'd be out of biz anyway.

What BLM value do you see while idling at operating temp in closed loop? Cruising at 30 or so MPH? The O2 sensor behavior your seeing may be normal, the BLM data will tell the story.

Note your idle BLM after a drive...come to a stop and note the BLM. The O2 sensor will be nice and hot, the ECM will have been sampling for a while and making adjustments so you'll see how much the ECM is correcting.

 

ok, all this guessing is pointless.

post ALL details about your engine. is ANYTHING modified? heads? cam? headers? exhaust? fuel pressure? runners? plenum? egr? PROM? flywheel/torque converter? rocker arm ratios? relocated sensors? thermostat temp?

perform a compression test and let us know the results.

who did your injectors? do you have another set to try?

If you have a problem, there is no sense ruling ANYTHING out until it's proven to not be the problem.

also. you need to absolutely and completely disregard anything your cute flashing LED air/fuel ratio thingy is telling you, because anything it's telling you is meaningless.

If you could post a few minutes log of the ECM output, that would be immensely helpful in solving your problem (or at least ruling out other problems).

 

I will try to get the car on a scanner again and right down some notes.

just for ****s and giggles I did take the car to the strip last night and it ran 14.9 @ 90. I was very suprised. We are talking a stock rebuilt 305 with headers and the smallest crane compucam, a converter and thats it. Rearend is 3.08 with dead posi. Anyway, I was impressed, I was forseeing 16's.