I've been dealing with a random miss for a while now, the longer I drive the worse it gets. I just got the ebl flash also, and thought it could be a tune issue. I'm pretty sure its an ign problem now. I have msd wires, and an accel cap and rotor. The miss comes and goes and changes cylinders under different conditions. Today I removed the cap, the cap and rotor look excellent, so I pulled the coil out of it, its an (hei), its it was kinda hot. I'm thinking it is getting hot and breaking down. It's original with an 83 date on it, so I'm gonna replace it. What coils are you guys running, I'm thinking accel or msd, any better ideas?

 

Think twice about running a high output coil with a stock ignition module. The high output coils run lower primary resistance and will stress the module. Best to use a quality stock replacement coil or think about upgrading to an ignition amplifier like the MSD. I tend to steer friends away from Accel ignition. The ignition amplifier drives the coil and uses the stock ignition module only as a crank reference. This will make the stock module last much longer while producing great spark KV and multiple spark discharge.

 

I think I have a msd 6a box laying around. I can install it and get an msd coil right?

 

That's pretty much it. I think the digital 6 is a better choice because it draws less primary current, meaning less strain the ICM. But even the analog MSD box will work.

As far as your misfire issue, don't neglect to check out the pick up coil and pole piece and timing core in the distributor. Also, when I diagnose a roving misfire, I often end up finding the cause to be fuel related. You don't specify what type of fuel system you have but since it's an 83, I'm going to guess it's carbureted. Check the throttle shaft bushings for lateral movement. When the bushings become worn, air can leak past them causing a lean condition at idle. Also, and I hate to even suggest it but, valve train wear, especially worn valve guides, or an eroded valve seat can cause intermittent loss of compression and an intermittent miss. You can find this with a running compression test.

 

On the hei dist, isn't the ign. Module all in one type thing? I'm using a tbi fuel injection and just got an ebl flash, I originally thought fuel also, but I've been from too lean, to too rich, and a miss has always been there in varying degrees. The top end of the engine is all new, so I hope there are no problems there. I'm hitting the junk yard for some other things today, maybe ill look for another coil there to try before I spend $100 on msd, and find that wasn't it.

 

The HEI system uses a magnetic pole piece and timing core to generate a small AC pulse as each cylinder reaches its base firing point. The pickup coil is positioned just above the pole piece and senses these small pulses magnifying them into a larger AC signal. The ignition module receives this AC signal and converts it into a primary ignition pulse to charge and fire the ignition coil and also into a digital square wave which is then sent to the PCM where it serves as a crankshaft reference signal. When the engine is cranking(rpm less than 200), the ignition module/ EST system operates in bypass mode where it operates without input from the PCM. Above 200 rpm the PCM, through the EST system, takes over control of timing.

Whenever I see an HEI with a roving misfire, I always pay close attention to ignition timing for inconsistent changes and may pull the distributor to check for lateral runout in the shaft and/or binding between the timing core and pole peice. When turning the dist, you should feel resistance as the points of the pole peice pass the points of the timing core. You should not feel any binding. The points of the two should not touch. If they do, replace the distributor.

 

Sorry to butt in on this thread. would the internals being off in the dist. cause a stall under load @ idle? I have this issue but when i un-plug the EST by-pass, it doesn't stall.

 

You should start by watching timing with a timing light while you snap the throttle. Look for a spark drop out or for the timing to retard with throttle. What you may be looking at is a knock sensor or circuit problem. If the knock sensor or any other part of the ESC(knock control system) is faulty, the system will command full retard(18 degrees) in order to prevent engine damage. This will kill power and may cause stalling if the engine tune isn't real good. Of course, the HEI distributor should never be overlooked as the possible cause of a problem like this.

 

I checked the dist. For lateral movement in the car the other day, but I think I should pull it now after hearing all that. I have noticed on the ebl display that the timing moves around a lot, and I've noticed it does move around more when it starts to miss. I always assumed that it was from the ecm making adjustments, but I'm new to all this. how much of a variation is normal at a constant engine speed? I guess I could unplug the est connector and see if it moves around, if it still fluctuates, the its the dist. For sure right?

 

The spark timing value shown on the EBL display (WUD) is a commanded SA value. At idle it can move around quite a bit as the ECM uses SA to stabilize the idle speed.

The ECM calculates the engine RPM from the distributor references pulses (DRPs). So if the RPM shown is jumping around, that can be caused by a bad distributor.

With the EST/BYPASS unplugged the ECM will still be calculating and commanding a SA value. The distributor will just ignore it though.

RBob.

 

I removed the dist. Today and took a good look, there is absolutly no lateral movement or binding, it turns very nicely, I reinstalled it and set the timing. With the est plug disconnected, and it doing its random missfire thing, watching the timing light, the timing is perfectly steady, I've been running and driving it while watching thr ebl wud, and have not had any est counts, so I think my circuitry is all in good shape. I found some ohm tests for the dist. Components, but not for the coil yet. Maybe that will be my next step before I buy a coil.
As far as the tune goes, I've installed a 7.4 tbi and injectors, and did not raise the fuel pressure to see if it is needed. On acceleration, the o2 voltage goes to 0, and my ve tables are at 100 in those parts of the table, so I know I have to raise the fuel pressure but at idle and cruise, I can go from lean to rich, and still have a miss, right now the o2 is switching, so the tune under those conditions at least shouldn't be too far out to cause a miss right?

 

Well, as usual with this car, a simple job just got harder! I set out to raise the fuel pressure, and things went down hill from there.
First I put a gauge on it and got barely 9psi. I thought ok, it is stock, so I removed the regulator and turned the screw to about half way and tried it again, now its down almost a pound, I turned the screw all the way to max pressure, and got about 8psi. With the engine running I pinched off the return line, and no pressure spike. I then removed and blew through the filter, which is not very old, it was fine, I checked pressure at the filter, 8psi. I installed a tpi pump a while back, I'm thinking the rubber hose in the tank may be ruptured. So I guess ill pull the tank and let you know what I find. I really hope this solves my missfire problem!

 

I pulled the fuel pump out and the hose was split, I replaced it, my next question is what kind of pressure should I be shooting for, I have no idea what kind of power it will make, mid 300's if I'm lucky. But is more better? Or should I have just enough to supply what is needed?

 

Best is your last thought, enough to supply the demand of the engine. Rough in the lower VE so that the vehicle is drive-able.

Then crowd the higher VE areas (RPM & MAP) and observe the resultant AFR. Adjust the VE as required to get it correct. While doing this observe the injector duty cycle (DC%). It should be kept under 86%.

If it is too low can decrease the fuel pressure, too high need to increase the fuel pressure. Once the injector DC% is in the right area, the fuel pressure is good to go.

The other item in this mix is the VE%, if it reaches 100 need to increase the BPC vs VAC table. And if the highest it ever is is less then say, 80, can decrease the BPC vs VAC values.

Think of the BPC vs VAC table as a centering device for the VE table.

While doing the above you are balancing out the BPC, VE%, fuel pressure, and injector duty cycle.

Now that there is enough fuel for high MAP/RPM, can spend the time on the rest of the tune. As the fuel pressure shouldn't need to be further adjusted.

Note that AE and proportional gains are PW based (not BPC based), so changing the fuel pressure affects those two items in the tune.

RBob.

 

Thank you! I'll do just that, I hope the miss will be gone!

 

I finally got the car off the ground, I took care of some other issues while I was at it. The fuel pressure is currantly at 21psi, I went back to a stock bin and started it up, got it into closed loop and started a ve learn in park, just ran it at different speeds and watched the corrections as a gauge along with the blm. I leaned the ve tables across the board and tried it a few times until I got it somewhat close. It is running better than ever! Never been so smooth! I can finally see this car has potential to be fun to drive! One last question, I've noticed all along while tuning, it seems that the longer I drive, the leaner it gets. It runs good as it warms up, goes into cl, runs better, and then starts going lean the longer you drive. How do I correct this?

 

Leaner, as in the BLMs increase? If so it is likely the fuel pressure is dropping off.

RBob.

 

The blm is going down around 108

 

Does the engine start to cut out? This is actually going richer and the ECM is bringing the O2 reported AFR back to stoich. Or so the ECM thinks.

If the engine is cutting out or sagging/stumbling, then the O2 is not reporting correctly to the ECM. A silicone poisoned O2 sensor will do this.

RBob.

 

It's definately going lean, it will start to surge and even pop through the intake sometimes on accel. I will do some more ve learns and see what happens, now that I have good fuel pressure, maybe it will be able to correct it.

 

VE Learns follow the BLMs when using that method. So they aren't going to help, just make it worse. Need to find out why the O2 signal is reporting rich, which is what is driving the BLM down.

RBob.

 

Ok, I was wondering about that, a lean missfire can make the o2 read rich correct?

 

I've seen that. WOT with not enough injector PW and the NB O2 reported North of 450 mV. Can't recall exactly, but it was in the 'OK area' of the rich side.

Poor WB was banging off the rails, hmm, something not right here.

RBob.

 

I believe what is happening is a lean missfire is still a miss with unburned fuel, making the exhaust flow having unburned fuel, causing the o2 to read it as rich. did some driving today and noticed that the ecm wants to remove fuel during cruise and decel, but I need more fuel during pe and ae. In ve mode it doesn't register any changes under any load conditions, even if I hold it there for a while, I'm thinking ill increase the ae and pe for now and see what happens.