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The moved my thread on issues with cylinder number six to another section. However, I need a tuning question answered.
I had (have) an issue with Number six plug fowling. Since the last post, I have replaced the Valve seal on the nr 6 intake, new plugs, new MSD wiring harness.
Initial test log run was going fine. Some 45 mph and some 75 mph time. Tune slightly rich, maybe .96 -.99 Lambda. Tuning is OPEN loop full time. Coming off the Freeway, engine almost died. WBO2 went major lean and changing back and forth. Ranges up to 1.8 or more Lambda. Barely got it home.
Key on, fuel pressure goes to 50 psi, settling back to 43 psi with regulator. Go to "Start", engine fires, fuel pressure goes to zero. Engine dies. Got to start a second time, fuel pressure dips down to about 20 psi, engine starts and remains running, PSI at 43.
Suspected bad regulator. Changed diaphragm. Took another test drive. Same issue, car ran fine with AFR Lambda .99-1.02 or so. Ten minutes, came to stop sign, Lambda went major lean, engine stumbling.
This sounds mechanical to me. Bad fuel pump, relay or filter. But, why does it run fine for a significant amount of time and then go lean. I want some guidance on ruling out the ECU causing anything. Being open loop, I don't think the ECU does any fuel management at all. AFR controlled by the VE table?
Things that happens as a function of time and are more or less repeatable, seem to be thermal-related IMO.
If I recall, this isn't a factory ECU. But open loop should be open loop... ECU pays no attention to the O2 sensor.
I also don't think it'd be the relay. Thermal degradation on the relay that would cause a large voltage drop should probably be permanent and visible by inspecting it.
Do you have an in-tank fuel pump? Or external? An external pump would be more prone to overheating...
The data log doesn't identify any voltage issues with the supply to the fuel pump, but that is only the voltage to the relay. I have a new relay, new fuel filter and new pump coming from Summit. I already replaced the regulator diaphragm. That should be the whole system.
. Attached are screenshots of the monitors in TP. Going out at about 45 mph and coming back at same speed. The WBO2 is the bottom bold red line.
The reason I put it here (DIY PROM) was I have been tuning this car for sometime and was trying to eliminate the potential of something from the "tuning" or ECU that could cause the AFR fluctuation.
If your harness is wired correctly, it is the voltage to the pump, after the relay.
The harness is from Street and Performance (out of business) about 27 years old. They provide a wire for the Fuel pump supply. When I built the car, I suspect I chose to run the FP relay from that wire with a lead from the fuse panel for primary voltage to the FP. There is no connection from the ECU to the FP power directly.
Do you also have the oil pressure back-up switch for the pump power?
Yes. I changed oil and oil filter immediately prior to the onset of the AFR issue. Oil pressure is good.
I checked the Oil Pressure Fuel Pump switch. I pulled the weathertight connector off the end (three wires) and found oil on the inside. I ordered a new one.
There seems to be some difference of opinion on the operation of the OPFP switch.
1. According to the wiring diagram. the OPFP switch is fed with Battery power. The output of the switch goes to the fuel pump directly (I know this because an earlier OPFP switch shorted out internally and killed by battery by running the fuel pump for a week in the garage)
2. The fuel pump is also fed by the relay. The ECU controls the relay. As long as the ECU is receiving reference pulses (i.e. engine rotation / running) the pump receives voltage from the relay.
3. If the ECU is calling for the relay to supply power to the fuel pump because the engine is running, what happens if you lost all oil pressure. What value is the oil pressure switch?
The reason I put it here (DIY PROM) was I have been tuning this car for sometime and was trying to eliminate the potential of something from the "tuning" or ECU that could cause the AFR fluctuation.
Not when the fuel pressure is swinging wildly. You have a mechanical issue.
The harness is from Street and Performance (out of business) about 27 years old. They provide a wire for the Fuel pump supply. When I built the car, I suspect I chose to run the FP relay from that wire with a lead from the fuse panel for primary voltage to the FP. There is no connection from the ECU to the FP power directly.
Both the FP relay feed and the FP oil pressure switch feed should be wired together and go to the battery (fused). This same fused power should also go to the ECM as the 'battery' feed. Then the output of the relay and OP switch get wired together and on to the FP. While at the same time that FP feed needs to go to the ECM.
This is how GM did it, and for good reasons. The FP voltage feed to the ECM is usually used for the injector voltage compensation. And for the FP relay malfunction diagnostic.
There seems to be some difference of opinion on the operation of the OPFP switch.
To test the switch unplug the FP relay while the engine is running. It should stay running with the same fuel pressure as the pump continues to run.
Which is the purpose of the OP FP back up switch. It is a back up to the FP relay in case it or the ECM driver fails. Nothing more, nothing less.
I haven't confirmed that the fuel pump pressure is swinging wildly, just know the AFR is going major lean and swinging. FP pressure is the most likely candidate.
Memory failed, but I found in old car papers the installation instructions from S&P. Their harness came with the Fuel Pump relay already installed on one lead and another lead for the OPSU. As mentioned before, the Original OPSU shorted and ran the fuel pump continuously for several days, killing a red top.
I suspect the wiring harness is consistent with GM design, know Mark Campbell and his company.
I haven't confirmed that the fuel pump pressure is swinging wildly, just know the AFR is going major lean and swinging. FP pressure is the most likely candidate.
Don
From your first/opening post in this thread:
Key on, fuel pressure goes to 50 psi, settling back to 43 psi with regulator. Go to "Start", engine fires, fuel pressure goes to zero. Engine dies. Got to start a second time, fuel pressure dips down to about 20 psi, engine starts and remains running, PSI at 43.
New OPSU switch, New Fuel Filter, New regulator diaphragm, new fuel pump. New injectors- a month or so ago. Same drill as before, drives fine until it warms up. Lambda at 101-102 or so. Then, off to the 115-125 range.
Once back in the driveway, Fuel pressure static at about 41 psi. A little light so moved it back to 43.
With all those replaced items removed from probable cause (particularly the fuel pump) what else could it be. Full time open loop.
How's your EVAP system doing? If the tank isn't being vented properly, could it be screwing around with the ability of the fuel pump to move fuel out of the tank?
Whatever it is, it's certainly appears to be time dependent when you get out on the road.
Unless some component in the ECU is starts too get hot and it starting to malfunction? Electrical components can start to malfunction as they age I'd imagine. But that would occur in the driveway or when on the road. And you say that it only occurs when on the open road?
Not sure that it is limited to on the road. I start the car, drive through the neighborhood as it gets up to operating temperature. Most of the roads around here are 45 mph, so am usually on one of those when it goes bad. But, it stays "bad" all the way back to my driveway and continues there. At idle in my driveway, you can watch the WB gauge rattle back and forth from .95-1.2 or so. Before whatever changed here, it would move around a little but not wide swings.
See Idle from Before and Now attached. WB at bottom
In your data, the final pulse width seems to be kinda erratic...
Took a look at your .csv data. This set of pulsewidths vs time is controlled for 1000-1500 rpm and 50-60kPa manifold pressure. For open loop operation, I guess I wouldn't expect that much variability within such a small range of engine operation. Something is causing the ECM to command these kinds of seemingly erratic pulse widths.
Also the AFR seems like it's just getting progressively leaner over time... not necessarily becoming lean all of a sudden?
I am not sure what to make of those Graphs. Are you thinking the ECU is commanding a change in the BPW. I thought in Open loop, the AFR was driven by the VE table (RPM vs MAP). The rising AFR over time might also correlate with rising AFR over Temp. Not specifically the coolant temp, but perhaps the engine compartment temp. These have been short test drives, so the engine compartment temp would be constantly rising during the drive. You cannot use MAT as I put in and Cold Air intake some months ago.
If the BPW is changing because of some command from the ECU, I would have thought an earlier BIN that ran great would eliminate that. The last good BIN that had stable AFR was BIN 131. The Current BIN is 135. Only changes really limited to VE tables. I loaded BIN 131 on the chip and tested it just at idle. Had the same erratic AFR on BIN 131 as I have on BIN 135.
The attached monitor from CSV 135b is a section of the log where most of the parameters for the engine are pretty stable. The WBO2 is all over the place. I went to the dashboard and stepped though this area and the AFR was all over, but not a big change in the BPW. I thought perhaps SA was causing some issues, but it's stable during this section. The WBO2 is only reporting data. I don't think the ECU is using the WBO2 information for anything.
What is the chance that one (or more) of my injectors is malfunctioning. They are batch fired. The harness is 28 years old. I think I can hear the firing with the stethoscope, but perhaps they have some issue that is limiting or preventing fuel from spraying. Perhaps something related to engine heat at the fuel rail. I have changed everything mechanical in the fuel supply since this started a couple days ago except the injectors.
I have another ECU on the shelf. I will swap it out tomorrow and see what happens. If that doesn't work, I still have the eight Original injectors. I changed them for the new ones when chasing Cylinder six issues. I will put all eight Original injectors back in and see what happens.
I am not sure what to make of those Graphs. Are you thinking the ECU is commanding a change in the BPW. I thought in Open loop, the AFR was driven by the VE table (RPM vs MAP). The rising AFR over time might also correlate with rising AFR over Temp. Not specifically the coolant temp, but perhaps the engine compartment temp. These have been short test drives, so the engine compartment temp would be constantly rising during the drive. You cannot use MAT as I put in and Cold Air intake some months ago.
If the BPW is changing because of some command from the ECU, I would have thought an earlier BIN that ran great would eliminate that. The last good BIN that had stable AFR was BIN 131. The Current BIN is 135. Only changes really limited to VE tables. I loaded BIN 131 on the chip and tested it just at idle. Had the same erratic AFR on BIN 131 as I have on BIN 135.
The attached monitor from CSV 135b is a section of the log where most of the parameters for the engine are pretty stable. The WBO2 is all over the place. I went to the dashboard and stepped though this area and the AFR was all over, but not a big change in the BPW. I thought perhaps SA was causing some issues, but it's stable during this section. The WBO2 is only reporting data. I don't think the ECU is using the WBO2 information for anything.
What is the chance that one (or more) of my injectors is malfunctioning. They are batch fired. The harness is 28 years old. I think I can hear the firing with the stethoscope, but perhaps they have some issue that is limiting or preventing fuel from spraying. Perhaps something related to engine heat at the fuel rail. I have changed everything mechanical in the fuel supply since this started a couple days ago except the injectors.
The ECM controls the AFR by altering the pulsewidth. If it's shortening the pulsewidth, something is prompting it do so, resulting in your erratic AFR's. It doesn't need to be in closed loop for this.
When you did your CAI, what did you do with the MAT sensor? If you moved it into the intake duct, then you need to go into TP uncheck the flag for
Switch 18 (0x018) - Bit 4 - Use Air Flow for Coolant/MAT Diff Multiplier from Table 0x80E
Otherwise the ECM is going to be mixing coolant temperature into it's calculation of final MAT temperature.
Unchecked and has been. BTW, the I did the CAI a couple months ago.
Tomorrow, I am changing the injectors first. I will double check the wiring. If that doesn't fix it, I will swap in the new ECU.
The only thing that was physically done between BIN 131 (Good test) and the appearance of the issue is that I changed a valve seal on intake six and installed new plugs and new plug wires. The next drive after those physical changes resulted in the AFR going haywire. But, I don't see a connection.
A gm module will go in the msd I think they soldered the pickup onto the icm.
that intake is super cool. I have the small block Version. Hope you figure out the cause soon without more hassle.
Another strange coincidence is the harness... I'm tuning a twin turbo 350 for a buddy, and he is running the exact same harness. His did not come with the relay or OPSU, so we were forced to use the factory relay. Same exact symptoms, sporadic fuel pressure loss, engine would run fine when cold, act up when warm... regardless if in OL or CL, would then stall during testing. Fuel pressure was not holding, brand new pump. Replaced injectors, fuel issue gone, pressure holding solidly.... but engine still acted up when warmed up, again regardless of OL or CL. ICM replaced with Accel aftermarket, issue got worse. ICM repaced again with GM replacement, car holds idle and no longer stalls. Does have a miss, but that's another issue, valve lash related. He just got his hands on a replacement factory harness as well.
One thing you could do to rule out the injectors is this (before buying another set)...
While the car is running and acting up...
Disconnect one injector at time. If you pull one and the engine gets worse, it's probably not the culprit. If you pull one and essentially nothing changes, that could be the culprit.
I went through the data again, scrolling through the various parameters vs time, and I'm not seeing anything where the ECM is getting a bogus input or anything like that.
Another thing to do is go back into closed loop and see if the ECM starts altering the INT/BLM. If not, then it probably tells you that the problem is localized to the WB side. If it does, it could still be something affecting the entire engine, or it could be localized to the NB side. But at least there's a possibility to rule out one side of the engine.
Before I made the following changes, the AFR was pretty stable. The next test run after making these three changes had the problem. I don't see how it is related, but...
1. Changed the valve seal on intake number six. Readjusted lash on intake at 1/2 turn with Exhaust valve just starting to open
2. Replaced old set of Taylor 8 mm with new set of MSD 8.5 mm. I crimped my own but did not check the ohm reading. I am going to do that today to confirm decent crimps.
3. New spark plugs
Next run, had the issue after about five minutes with erratic AFR and going off the chart lean.
Next
1. New fuel pump
2. New diaphragm in the regulator
3. New OP switch
Next Run, no change still erratic AFR and lean after five minutes or so. AFR gets leaner with heat/time
Today
Pulled new injectors and replaced with the original good injectors. Check harness at injectors (against each other) with ohmmeter for broken wire. No issue. Fuel rail would not hold pressure. Took the regulator apart and found a chrome plate chip inside, suspect it was blocking the closing valve in the bottom of the regulator.
Test drive, still erratic AFR after five minutes or so, but not so lean. Range from .88-1.10. But appears to go lean with heat/time.
Changed ECUs, no change from last test drive.
If I understand what you said, you were working with a Street and Performance harness. I think Mark Campbell made two types, as I have two sets of instructions. The harness I have came with the FP relay and the OP switch.
It sounds like you change the ignition control module with factory GM and it resolved the issue.????
See my last post on the replacing the injectors. I have purchased new ones when I suspected a bad injector for the Number 6 cylinder fouling issue. The old ones were cleaned and flow tested not that long ago. Replacing all eight and finding a chunk of chrome plate in the regulator seems to have lessened the Lean issue, but the AFR is erratic, and it runs rugged.
Don one thing to remember is that a Rich condition will often read Lean with a wideband if it is severe enough. Did you get the chance to pull your spark plugs and look at them to see how they are burning? In my friend's case, it was very odd that after installing similarly new wires, cap and plugs, not too long affter... number 5 and number 6 under the cap had severe discoloration, yet the rest along with the rotor were fine. In his case, after exhausting the basics; compression/leakdown test, etc, we thought maybe he cracked porcelain in plugs 5 & 6, but they were again replaced and still have the same issue (missing). The pressure, it turns out, was because of ebay injectors. Southbay provided much better 80# injectors, and even after multiple offsets tried, still having issues with missing, but pressure is fine, again only when warm though. The harness is coming today, should be installed sometime tomorrow, will share the outcome after the install if interested...
This is really depressing. I had another thread on number six plug fouling. I have changed injectors, distributor, removed and reinstalled the intake manifold, new spark plugs (three sets), new plug wires and a new intake valve seal on number six. The new valve seal, plugs and wires was just before the lean issue.
Pulled the new plug wires today and check with ohmmeter. All good
Pulled number six plug and number three plug (easy to get in and out around the headers.
Guess which one is number six...........Maybe 25 miles or so..
I have addressed fuel and oil from the lifter galley and intake seal. What's left?
This was a new Short block from GM ZZ502. Not cheap. I have had this issue with number six almost the whole time. I have exhausted the upper end stuff. Leak down and compression are good, but sure sounds like ring issue.
I agree, time to pull it back down and find the issue. The problem is that the engine compartment in the 38 is really puny. I can see the front of the engine, or I can touch the front of the engine, but I cannot do both at the same time. Plus, I don't have the shop room or hoist like I had in Colorado before moving the VA. I know, sounds like whining
