1992Vortec

Hey guys i moved up to 10 PSI did the first pass and had to pedal the car into second due to being sideways on a 2 lane road. When i did this the car back fired through the intake and kicked a CEL for EST. I cleared the code and test drove under light load with no issues. naturally i parked the car and jumped on here lol. Never had any codes before this boost pressure change. Running a EBL P4 and i check all wiring connection mainly DIS and timing connector and all seems well. Anything ideas thanks guys.

junkcltr

iTrader: (1)

That ECM is a GM unit with a few mods. If it was GM hardware and code we could help you out but you have proprietary hardware so you have to go to the manufacturer to get the info you seek.

RBob

iTrader: (1)

The real question is, did the backfire cause the EST malfunction, or did the EST malfunction cause the backfire. My guess is that the backfire caused the EST malfunction. It takes very little for the ECM to see that the EST may not be correct.

How much fuel was in the tank? It is too easy for fuel slosh to uncover the pickup and go lean, which can/will cause a backfire out the intake.

Check the entire ignition system as an issue there can also cause a backfire. Cap & rotor are obvious that needs checking. But also the spark plug wires, boots, spark plugs & gaps.

Even more important is the condition of the pickup coil, the magnetic 'star wheel' and ICM. Regarding the star wheel, check that the magnets aren't cranking. And that the wheel is still solidly attached to the shaft.

Check that the base plate that the cap attaches to is also still solidly attached to the distributor body.

RBob.

Street Lethal

iTrader: (16)

I'm sure it was just intermittent, but I would still carefully re-inspect your DIS connections, wires, coil resistance, etc. How does 10-psi feel to you? Just wait til you hit fifteen...

1992Vortec

This is exactly what i was thinking the chicken or the egg concept. I think the backfire caused the light i will double check everything i am using a MSD DIS that i heard can be worse than the stocker... and i did have a little less then a 1/2 tank so i will fill up log and retest. What exactly is the ECM seeing when this event happens?

1992Vortec

It scared me lol i replaced the spring in the WG and was staring at the boost gauge during the first pull to make sure it wasn't higher than 10PSI when i looked up i was nasty sideways haha. Im going e85 early next month with a gear change i cant imagine 15 PSI with a lot more timing its going to be fun!

RBob

iTrader: (1)

Checking your other thread I noticed the MSD distributor and coil. The MSD wires are likely OK, but I'd use a GM distributor and coil over any aftermarket stuff. Along with the mandatory GM ICM.

There are two ways to set code 42, during cranking and then while running. The ECM counts the EST (electronic spark timing) pulses it sends out to dwell and fire the coil and compares the count to the incoming count of the distributor reference pulses (DRP).

If EST pulses show up during cranking then the distributor hasn't clamped the EST line and that is a code 42.

While running, if the count of outgoing EST pulses doesn't match the incoming count of DRPs, that is a code 42. And it doesn't take much to set this code, one miscount and it's a malfunction.

The backfire jarred the engine good, easily upsetting the distributor.

RBob.

anesthes

iTrader: (12)

How ?

I've been trying to wrap my head around this for a few minutes.. I guess I'm not that smart.


-- Joe

RBob

iTrader: (1)

With the engine at WOT and accelerating the timing chain, camshaft, distributor and oil pump are in a steady state of also accelerating. The slack in the timing chain, cam gear and distributor gear, and oil pump is all taken up.

With a backfire in the intake system the engine misses a beat, a serious skip. Suddenly the timing chain, cam, whips back transferring that 'skip' to the distributor.

To find that spot in a data log, just look at the MAP sensor value. When it spikes to the maximum value you found the backfire.

RBob.

anesthes

iTrader: (12)

So the next DRP is either grossly too soon or too late, and the ECM sets a code?

-- Joe

Street Lethal

iTrader: (16)

Bob, is it the same as saying that when the engine backfires, the ECM momentarily see's no RPM, or below 400-RPM within that specific moment, but at the same time see's voltage applied to the EST line, so the code is intermittently set...?

anesthes

iTrader: (12)

I don't know what the code looks like, but I'm assuming it's a loop around a timer.


I don't know how many hz the loop runs at, but it's reading DRP's and commanding when to fire the trigger. I'm guessing it either sees a DRP it doesn't expect, or doesn't see one within the timeout window and sets a CEL code.

Interesting. Ford actually does the quite opposite. If REF is lost the ignition module will keep the last requested advance for several seconds until the timeout window is reached, then will fall back to base 10*.

-- Joe

RBob

iTrader: (1)

The most likely scenario is that the EST line was high which is dwelling the coil. The engine backfire causes a false DRP as the distributor star wheel is kicked.

The false DRP causes the hardware to reload the EST counters. In this case there is an extra DRP pulse without the corresponding EST pulse. Code 42 follows shortly thereafter.

There isn't any firmware loop looking and waiting for DRPs to arrive. That is all handled in the hardware. Same for firing the injectors. Although the firmware does get involved when the injectors are in single fire (S/F) mode.

RBob.

1992Vortec

RBob,

Thank you as always for your great customer service on you product. I topped the tank and gave it another pull with no issues. Drove it around 50 miles (beating on it) with no problems must have been the fuel sloshing around. If i could get traction in 1st or second the car would be fast lol