Voltage or Fuel Problem??

[WyoSyclone]

Well, I've been tuning with Code59 for quite a while now and have run up against an issue that I'm wondering if anyone has seen before.

What I'm experiencing is almost like a high RPM flameout... I've attached a jpg that shows what I'm talking about... as the Sy is accelerating the RPMs (top red line) are stepping up and down with the overall increase in engine speed. This 'wavering rpm' covers about 75-100 rpm. This issue is REALLY holding the truck back from making some good runs.


In this image you can see where ignition voltage (flat blue line), Injector DC, and BPW are all inter-related with respect to the wavering rpm.

Recent new items are: NGK ur6ix's gapped at .028, new cap and rotor, new ignition module, new Accel factory-type coil, new Magnecore wires, new alternator.... I've taken every B+ and ground wire in the engine compartment and taken it off, burnished it with my dremel tool, reconnected with star washers where needed.

System voltage during a run: between 12.9 and 13.4
Fuel pressure: 48psi while sitting (I don't have my cab-mount FP gauge installed yet).
AFR's in the above frame ~11.4
Boost only ~12psi on this run with "0" WGDC

My theories:
1) The truck really doesn't have a 255 pump in it like I was told it did, though I would think BPW and Inj DC would be higher if it were running out of fuel.
2) The RPM Stage1 is moving enough air that the turbulence at the outlet of the internal wastegate is great enough to be causing back-pressure spikes.
3) Partially clogged CAT may be causing back pressure issues.
4) ECM going bad?
5) Some other electrical gremlin.

Has anyone else seen this same issue?

Thanks for any ideas you may be able to offer

 

[WyoSyclone]

Re: Voltage or Fuel Problem??

I thought Accell coils were to be avoided at all costs. My not cure your problem, but I remember from WAY back there were lots of issues with the Accell coils on these trucks.

I'm not sure.... I did switch back to the stocker and had the same problem. I only went with the Accel because it had a little better specs and had a brass post rather than the aluminum. Thanks for the input... I'll keep it in mind if it ever seems like it's starting to crap out on me.

 

[sy#2921]

Re: Voltage or Fuel Problem??

Did you do the relay voltage mod? i know it smoothed out some voltage swings I was having along with the false knock issue.

 

[WyoSyclone]

Re: Voltage or Fuel Problem??

Did you do the relay voltage mod? i know it smoothed out some voltage swings I was having along with the false knock issue.

Are you talking about the feed to the ECM? Do you know what level your voltage was at when you were having the false KR?
On Dig's suggestion I was going to do this anyway, but I didn't think the voltage running around 13 would cause the running issue.
Also I was thinking about breaking the injectors out of this circuit and running them off of a relay-isolated feed because they seem to be the heaviest current users on that circuit.

 

[sy#2921]

Re: Voltage or Fuel Problem??

Before My voltage reading on tunerpro was never more than 12.5 volts. At part throttle it was dropping into the 11's even. Since the mod I have not seen anything less than 13.4

 

[cloneman315]

Re: Voltage or Fuel Problem??

i did the voltage mod a few years back when phil and i were just starting to run the moates chips etc,and i know it did fix my truck as well as his and a few others,this might not be it but it is def worth doing.I think if yah do a search i posted how to wire it up.

 

[cloneman315]

Re: Voltage or Fuel Problem??

as the injector dc increases voltage will drop,but your running a fairly small injector so this might not be it,but may be worth trying.and cant hurt.

 

[Don W.]

Re: Voltage or Fuel Problem??

FWIW dept. I disconnected the ECM and put a volt meter from the hot to grnd at the connector. Wiggled the ign sw and was able to make the volt meter dance around a bit. It varied, maybe a volt - volt and a half. The fact that it varied at all is what bothered me. I changed the ign sw and it went away. Just something to check. I have a thread of hints if you decide to change it.

HTH

 

[WyoSyclone]

Re: Voltage or Fuel Problem??

as the injector dc increases voltage will drop,but your running a fairly small injector so this might not be it,but may be worth trying.and cant hurt.

Thanks for the info!
I just made a few more logs about an hour ago... strange thing is my ign voltage, inj DC, and rpm all rise and fall together....if my inj DC goes from 57.8 to 57.9 the ign voltage goes from 13.0 to 13.1, and rpm goes from 3100 to 3200...

My AFR's are steady so I assume I'm not running out of fuel... otherwise inj DC's would be able to correct and hold, right??

So, I guess that might just leave isolating the ignition feed to the ECM... the ignition feed to the injectors is on the same circuit! Why did GM do that?? :rant:
Instead of making a new feed for the ECM (taking it down from behind dash, etc.), it looks like a much easier method is to just relay isolate the injectors at the pink/black wire in the 3-pin connector beside the AFPR. The battery junction block is right there to pull B+ from and the injector feed can act as the trip for the relay....doing this would leave the factory lead supplying only the ECM with ignition (I'm assuming that it's the current draw of the injectors pulling the voltage down on the ECM ignition lead).

Please punch me if I'm overlooking something

 

[cloneman315]

Re: Voltage or Fuel Problem??

i have seen that happen a few times the voltage makes everything wack out,i would try it .

 

[WyoSyclone]

Re: Voltage or Fuel Problem??

FWIW dept. I disconnected the ECM and put a volt meter from the hot to grnd at the connector. Wiggled the ign sw and was able to make the volt meter dance around a bit. It varied, maybe a volt - volt and a half. The fact that it varied at all is what bothered me. I changed the ign sw and it went away. Just something to check. I have a thread of hints if you decide to change it.

HTH

Thanks Don, I think that's a good place to check too.... I've had a few instances of the truck not wanting to start when warm (the infamous purple wire issue), but in my case I've been thinking it may be ignition switch related (I just got done pulling the park/neutral switch and recalibrating it to make sure it wasn't causing the start issue).

I'll do the relay isolation of the ignition feed to the ECM and if that doesn't solve it I'll look at your threads on the ignition switch swap.

 

[WyoSyclone]

Re: Voltage or Fuel Problem??

Well, I just did another data run, after having relay isolated the injectors from the ECM. The good news is that the "ignition voltage" at the ECM now stays at exactly 13.5 or 13.6 and never varies from there, from idle through WOT :woot:
.... The bad news is that I still have this damn variation in my Inj DC and Inj BPW, causing the RPM to fluctuate under WOT.

Me thinks I may be looking at a fuel supply issue. :banghead:

 

[skipztt]

Re: Voltage or Fuel Problem??

fuel filter????

 

[cloneman315]

Re: Voltage or Fuel Problem??

sorry man ,you will get it,but that mod does help big time

 

[WyoSyclone]

Re: Voltage or Fuel Problem??

fuel filter????

That's definitely the easiest thing to check.... so it's off to the parts store tomorrow

 

[WyoSyclone]

Re: Voltage or Fuel Problem??

sorry man ,you will get it,but that mod does help big time

Yup, it's awesome seeing that voltage stay rock solid! :tup:

I'm really wondering if this thing has a 255 pump in it.... I'll try the filter first and if that doesn't cure it, it looks like it's time to pull the bed off
I've been wanting to get into the tank for a while anyway cuz my fuel gauge reads way off (by 1/4 tank).... I thought cleaning all of the ground might have cured it (I think it helped, but it's still not right).