lionelhutz

Do you just keep running it or do you disconnect the battery before each test?

It still sounds like it's going lean under load or the ignition is breaking up. You might have a vacuum leak or injectors that aren't adding enough fuel.

Take it for a drive and hold it at a constant %TPS value and watch what the BLM does as it learns the fuel trim. I still see the BLM reaching 135+ in the log data where it appears you're just cruising along which indicates it's really lean and adding a lot of extra fuel.

The BLM is likely a 3 x 3 table so it gets adjusted in the cruising range which can help add fuel. However, when you go WOT you hit the corner cell where it hasn't been run in closed loop enough (or at all) to have any learning. So, the ECM basically ends up in open loop with no fuel learning when you try to go to WOT. If it's lean and has to learn to add fuel in closed loop then it'll likely stay lean at WOT.

Did you verify TDC so you know the timing is correct?

alconk

Well if you removed the plug in the regulator port then what I did to get the pressure was did it off the car. I have the tool for adjusting but it's worthless and like you say you risk ripping the diaphragm. With mine I was able to turn the adjusting nut until I could no longer turn it then re-assembled. That gave me 14psi.

Red1990VT

I have been disconnecting the battery each time I change something, and also/especially when dealing with removing or reinstalling the ignition module.

When the ignition module was tested, it was run without any provision for vibration and only run once. The store was busy, maybe I'll go back again at a different time and ask to run it over and over to get it hot. I didn't see any tools or provision for vibration, but I'll ask.

The car does seem to be going very lean under load, and I haven't ruled out the injectors. I did talk with someone at Injector connection about that. Since the car can bury the speedometer on the highway (level or downhill) he felt the injectors were probably able to supply plenty of fuel. He did say I could still send them in for flow test and refurbishment, and I'm leaning (no pun intended) toward doing just that.

I thought I read somewhere than the 1982 Corvette goes open loop at WOT. What Lionel wrote about close loop learning at WOT is new to me. If I can find where I read that about WOT being open loop, I'll share it. (I also recall something about the transmission in WOT and (again, I think) open loop in the 82 that was corrected for 1984, but can't recall what it was - had to do with WOT and shifting and top end speed).

I did not verify that TDC is really TDC, so it is possible that a timing issue might still be at play. The car has no audible knocking, and behaves fine under every circumstance except opening the throttle uphill or very abruptly on level ground...so I've been assuming (perhaps wrongly) that the car is timed correctly.

Funny thing overall is the car will accelerate very smartly from a stop, and the stumbling and hesitating seems to be mostly after 30 MPH and uphill. From a dead stop the car will accelerate uphill strongly...until about 30-35 MPH, then the problem manifests itself and if I don't feather the throttle the car stalls out.

RE Take it for a drive and hold it at a constant %TPS value and watch what the BLM does as it learns the fuel trim. I still see the BLM reaching 135+ in the log data where it appears you're just cruising along which indicates it's really lean and adding a lot of extra fuel.

I'll try to do this and get some data.

Thanks all...I really appreciate everyone's help and thoughts

Red1990VT

Yes, that's probably a better way...I did notice when I got it back together that the spring was very compressed with little adjusting room left...might be enough to eek out another PSI or so tho. If I can work up the courage I might pull it back off, remove the plate/plug, and try for 14. The only hesitancy (again no pun intended) is that going from 11 to 13 did not seem to have any noticeable effect. I wonder if one more PSI would matter...maybe it would be the threshold that needs to be crossed.

alconk

I could be wrong but probably 1 psi won't make a difference. I just think after you find your problem the 14 psi will allow the car to run better.

Now you mentioned that the car accelerates strong until around 30-35, do you recall what RPM you're at and has it yet shifted into 2nd? So going up hill does the problem always occur at the same RPM and if it does have you tried manually shifting down a gear? I'm wondering if the problem is in a certain RPM band.

Red1990VT

By the time I'm heading uphill on the route I use to test the car, I'm usually already in fourth gear overdrive. The car starts to bog and I drop it into third, and it is better but still stumbling and hesitating and I have to feather the throttle to keep the car from stalling out - which it occasionally does.

I've noticed the problem seems to be worst around 35 MPH and (memory here) around 1200 or so RPM, heading up hill.

Also, there is a perceptible roughness to the car even on level ground at 35-40 MPH, not an outright misfire but at that speed and RPM level, I'd imagine misfire(s) would be noticed as a roughness. I've noticed that entire Cardone distributors for the car are available for about $100, including the cap, rotor, modules and mechanical assembly. I don't like to throw parts at a problem, but I'm beginning to wonder if putting that assembly in with new wires and plugs might be prudent. The distributor and associated parts now in the car appear to be the originals (besides cap and rotor, which I replaced along with plugs and wires when I bought the car in 2009). So it might not be unreasonable to simply consider this replacement normal maintenance (especially the coil) and see if a difference is made. The total cost even if the problem persists is low enough to proceed...so I'm considering it.

Another thing I'm thinking about is whether to replace the O2 sensor, even though the data log indicates the one in there is bouncing back and forth as it should. Perhaps it is the original too, and some question exists as to how responsive it might be under load...

Anyway, I hate to resort to throwing parts at the problem, but the distributor assembly, wires and plugs and O2 sensor (if really from 1982) could stand changing anyway.

Red1990VT

Well, could Probably stand changing anyway

terry82

I have replaced my coil .it did seem to start better with the new one.

alconk

Wow if you think the 02 sensor is original I would have tossed that along time ago. I understand about just throwing parts but that definitely needs changed if it's original. I had mentioned earlier that I installed a heated 02 just because it was taking so long to go into closed loop. For me that made a big difference keeping it in closed loop.

gungatim

if your pressure is in spec, what about flow? you could have the correct pressure but not be putting out enough flow and still starve for gas. here's a thread discussing the issue below.

https://www.corvetteforum.com/forums...fuel-pump.html

lionelhutz

The pump won't maintain 13 psi if it can't produce enough flow to properly supply the engine.

Red1990VT

Hi again everyone...

The O2 sensor may be original, not really sure. It does seem to bounce around in closed loop the way it should, and since it is likely to be a colossal pain to replace I've been holding that in reserve. It may be old or even original, but does seem to be acting properly...which is why I've been thinking about replacing versus actually having done it...

The fuel pressure does seem rock solid no matter what is going on with the car, including when it is stumbling under load.

I did put heatsink grease on the ignition module when I returned it to the distributor after having it tested. Thanks for the reminder tho.

Attached are some lastest data runs as well as the O2, INIT and BLM tables. I'd appreciate if someone would help me interpret the O2, INT and BLM tables just to be sure what I'm thinking is in line with what more experienced people here think.

One of the files has a blue highlight where the car kicked into closed loop, around 125 degrees F, so while a heated O2 sensor might be good, it does not seem as though this car needs one. Seems to get into closed loop in pretty short order. At which point the O2 sensor goes from hanging around half a volt to bouncing from around 0.1 to 0.9.

I won't keep drowning everyone in data, but any thoughts on these latest files would be appreciated.

Thanks

lionelhutz

It looks lean. You don't have many data points though.

The O2 in the 90-100 map columns should be pegged very close to 1V though.

Red1990VT

I really wish WINALDL had the injector pulse widths included...then we could tell if it is lean because the ECM/PROM combination is commanding lean, versus commanding a richer condition that never happens because of a fuel injector problem or fuel quantity (flow, pressure) problem.

Red1990VT

I've been distracted for almost a month and the car has largely been sitting, needing front brakes...but it finally hit me like a ton of round tail lights...I think the problem MIGHT be play in the throttle plates (the need to sleeve the throttle bodies). I was backing the car out the other night for a short drive just to run it up, and boy did it ever remind me of what started this post. That's when I realized, no codes, good fuel pressure, good spark, all the usual suspects checked and re checked...still, the infamous bucking and stalling problem. That's when I recalled seeing the TPS come back to different values when I let off the gas (even shows up in the data runs)...the play in the throttle plates may be allowing more air to enter on side than the other on acceleration, even tho the units are properly balanced at idle.

I don't know where to get the throttle bodies sleeved now that DCS (Renegade people) seems to be gone. If anyone has a suggestion on this, I'd appreciate it. This may not be the answer, but it certainly seems like a pretty good bet...

alconk

Is there play in the shafts? Generally that leads to erratic idling problems.

Red1990VT

Oddly enough the car seems to idle fairly smoothly most of the time, although there is the occasional what feels like a miss or roughness. There are occasions where the idle does fluctuate by a couple hundred RPM in neutral, but that's not the rule.

What triggered the thought was letting off the gas while moving, with WINALDL running, and seeing different TPS readings for what should be a closed throttle. Manually it is set for .525 volts, but while driving I see .2 to .7 as a closed throttle reading.

And when I got the car, the problem was so bad the car was undrivable until I balanced the throttle bodies. That helped, but (as this thread shows) never really got rid of the problem completely.

I'm willing to try bushing the throttle bodies (for a reasonable price, I'm not spending a couple hundred dollars each) and see if that fixes this once and for all. I know DCS used to do this, and a local machine shop might, I just need to figure out the best and most economical way to give this a try.

lionelhutz

If it was an issue, the issue would occur at high vacuum and low throttle operation and go away as you transitioned to lower vacuum and higher throttle operation.

terry82

I don't think this is your problem but any carb repair shop can do your bushing fix .

Red1990VT

Update to this thread...I had been diverted from this matter for some time, but finally returned to it about two weeks ago. I had been occasionally driving the car, and the front brakes locked up about a mile from home. Long story short I ended up replacing the front calipers, pads, brake hoses, and the front drivers side hardline. What a job, but done well and the car is back on the road, stopping like a Corvette should.

I had bought an extra crossfire manifold with throttle body assemblies some time back off ebay. To test my theory that the shafts might be the source of the problem, I decided to swap the throttle body bases with what was on the car. It's a bit of a job, and took about three hours in total, but I got it done, balanced, and the TPS reset properly. While these throttle bodies are not new or sleeved, they did appear to be in better shape with subjectively less shaft play than what was on the car.

The difference was very noticeable, and the problem was greatly improved, though not eliminated. Any sudden sharp motion on the gas pedal could still induce the stumble, although with a very smooth foot, the car accelerated smoothly and well. I think what happens is any sudden or sharp pressure causes the throttle plates to open at slightly different rates, inducing the stumble.

The car is the best it has ever been, and very liveable. I could simply live with the residue of the problem, or send out the spare throttle bodies for sleeving, and then reinstallation.

I won't do either, because I ended up selling the car, having carefully explained and disclosed everything to the buyer, including a test drive to demonstrate the behavior of the car. And letting the new buyer drive and understand what he was going to be dealing with. We ended up cutting a deal that was fair, and i even threw in the factory service manual after the deal was made.

Having previously sold my 1984, I no longer own any crossfire injected Corvettes. The new owner understands that the throttle bodies shafts play may or may not be the cause of what remains of the problem, and I wish him well if he decides to continue solving it. Meanwhile I am down to a 1990 that needs fuel injectors, and a 1978 that needs a windshield.

Thanks to all for trying to help with this. In the end, a lot of progress was made and the problem while not completely solved was greatly improved. To the point it could simply be lived with if the new owner so decides.