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EBL Flash Pin-R ECM Reference Signal STILL Unstable!?
DFI and ECMDiscuss all aspects of DFI (Digital Fuel Injection), ECMs (Electronic Control Module), scanners, and diagnostic equipment. Fine tune your Third Gen computer system for top performance.
EBL Flash Pin-R ECM Reference Signal STILL Unstable!?
I'm about ready to push this car off a cliff at this point. I've been battling this issue for years going way back to when I was still running HEI only with no CD ignition box. I've tried everything. Made sure I ran the correct resistor spark plugs, 300ohm per foot shielded spark plug wires and etc. GOOD grounds from battery to chassis, battery to engine block and engine block to chassis all with 2AWG cable. The latest thing I did the other day was remove my Davis Unified ignition module from the distributor and replaced it with a NOS ACDelco module which made the RPM signal seen in datalogs arguably WORSE and now the car has a very noticeable decrease in performance/acceleration around 5600+ rpm so I'm putting the DUI module back in. Here's the problem. Take a look at the below datalog. I know the fueling needs to be leaned out but ignore that. Look at the blue line (RPM signal):
WHY does the frigging signal look like this under load!? Note that this is only visible on the ECM side. The vehicle does not "feel" like the rpm is oscillating under acceleration and it does NOT show up at all on the tachometer. The symptoms I'm having are the spark and fuel limiter coming on several hundred RPM early from what they're commanded at and I know it's not helping the fueling calculations any. Would adding a ground strap from the distributor base to the chassis help or hurt the issue? At this point the only other thing I can think of is running a new lead from the R pin of the module straight to ECM in hopes that something somewhere along the way is interfering with it.
Re: EBL Flash Pin-R ECM Reference Signal STILL Unstable!?
Note that the R signal (REF High) is paired with REF Low. Which is a ground at/from the distributor. The R input to the ECM uses a differential amplifier which uses both REF High and REF Low (can also be shown as REF+ and REF-).
Things to check at the distributor (large cap?), that the star wheel is firmly attached to the distributor shaft. The magnet in the star wheel is in good condition. No excess shaft to distributor body/bushing clearance. The pole piece is solid and not movable.
It could be a bad pickup coil.
Make sure that the wires between the distributor and ECM are not near any spark plug wires.
Some others items are the valve train and oil pump. Both of them affect the distributor.
Re: EBL Flash Pin-R ECM Reference Signal STILL Unstable!?
Originally Posted by RBob
Note that the R signal (REF High) is paired with REF Low. Which is a ground at/from the distributor. The R input to the ECM uses a differential amplifier which uses both REF High and REF Low (can also be shown as REF+ and REF-).
Things to check at the distributor (large cap?), that the star wheel is firmly attached to the distributor shaft. The magnet in the star wheel is in good condition. No excess shaft to distributor body/bushing clearance. The pole piece is solid and not movable.
It could be a bad pickup coil.
Make sure that the wires between the distributor and ECM are not near any spark plug wires.
Some others items are the valve train and oil pump. Both of them affect the distributor.
RBob.
Thanks for the response.
Put the DUI module back in yesterday. The distributor is a DUI turnkey and has around 9k on it. Everything still looks brand new inside. Can remove the cap to verify condition of star wheel. I too have considered the possibility of a bad pickup coil but am sort of reluctant to go through the trouble of replacing it only to see that it hasn't fixed anything
Yes, it is a large cap HEI. Primary coil resistance measured at 0.3ohms. I did add a ground strap from the distributor body to the chassis yesterday for the hell of it but have yet to do another log.
Oil pump is a Melling M55 standard volume. Timing chain I would assume is still tight (Double roller). The entire engine only has 6k miles on it.
Re: EBL Flash Pin-R ECM Reference Signal STILL Unstable!?
Hopefully I'm not digging anything up from the dead here.
I felt it necessary to share my experience with a similar issue. I've been dealing with some RPM flutter as well. Even at idle, the tach on the WUD was fairly smooth, but every now and again I would see the RPMs jump way up to over 2300 for one frame. It was pretty annoying, and did (slightly) affect the smoothness of the idle.
I'm running a small cap distributor with the '369 ICM, MSD digital 6A, Blaster II coil. I started by checking all wires around the distributor making sure nothing was coming close to a plug/coil wire. I accidentally bumped the 4-wire connector, the one with the DRP signal, and noticed the plug was loose in the socket. Somehow, the silicone weatherpack part was gone. The plug was flopping about, barely clipped in by the tab on the top of the ICM. This. presumably, was causing an intermittent poor connection. I went to my parts car and grabbed the silicone piece off the harness. I put it on the plug, plugged it back into the ICM, and my flutter vanished. Everything is silky smooth now, with no jumps in the RPM on the WUD or tach.
06-15-2019, 12:38 PM
