I’m fairly certain I have at least one, and possible three injectors that just don’t want to behave. I’ve been chasing a random misfire for three years now. I know cylinder 3 is misfiring up to four times as often as the others from logging misfire history. But, others also show a significantly higher number of misfires, and it appears to be totally random in nature, as some logs have completely different misfire events. I put together a spread sheet to compare logs, and some logs show more events than cylinders during the previous logs, while other cylinders show fewer than previous logs.
As stated, the missfire is random. No rhyme or reason. Definitely a misfire, and not just surge or reversion. Above 2500 rpm, there is none and the engine smooths out. It feels like I have a burlap bag filled with clothing being dragged behind the car and it just kinda bounces along behind the car at an erratic pattern, but not nearly often enough to be reversion. The other thing that tells me it is a misfire, and not reversion, is I can hold a steady throttle position at 2200 rpm, it can still feel it. But it’s not missing every 100 milliseconds on the dot or any regular time period. I find it doubtful that I’d still feel reversion at 2200 rpm. The cam isn’t that big.
But anyway, not ruling out reversion, or anything at this point, I’ve done the following things to try and eliminate this.
I initially tried moving spark around from as low as 24 deg, to as high as 55 deg in the areas where this is occurring. Still there…. Tried matching all spark tables in this low rpm/low cylinder fill area of the table, no good. There are no spark dips that I can see on the logs. Spark is smooth as butter with no dips….
I logged voltage, and it was 14v, consistently.
I have checked all ground connections I can find, and they are tight.
Last spring I thought it might be a valve spring, so I checked them and they were all good. Found out the valve guides were toast, the combustion chambers and pistons were coated with burnt oil / carbon, so I thought that was the problem! I shipped the heads off and had them overhauled. G-damn miss is still there. NOOOOOOOO!!!
I have changed plug wires, changed three coil packs on the three worst offenders, changed plugs from NGK TR55’s to TR7’s to Denso IT22’s, and now back to the TR’7s. I’ve also changed plug gaps from as high as .050 to as low as .030. When I pull the plugs, they always look good, with none of them being noticeably different than the rest. None of that made any improvements.
Then I thought it might be turbulence between the FAST intake runners and head ports, so I port matched all of them…. While I had it apart, I thought it could be a vacuum leak, so I put all new seals in it. No change.
I then figured it must be fueling, so I recalibrated VE (I have the custom OP system). Every damn cell I can hit is under 2% error, with most under 1% now. That didn’t cure it.
So then I recalibrated MAF. MAF is not as good as the VE table, as the STFT error was a moving target at any rpm under about 2500. I thought I might have a bad sensor, so I changed it out with a new sensor. That didn’t do any good.
MAF error is now under 2% if I’m in a lower gear, higher revs, but it goes to crap the first half of the low table in fourth or higher. Not real sure if that can be resolved with a cam that has as much overlap as mine does.
The car had a K&N CAI, so I swapped that out with a MF103 with beehive, thinking the MAF forward design might help. That did not help.
I then thought it might be a flaky O2 sensor, so I changed them out with some new NTK sensors. No change.
I have checked the engine and exhaust for vacuum leaks with smoke. No smoke sucking anywhere.
Then I thought it could be the TB, as a “tuner” ported the OE 92mm TB. So I sent that out to VMax and had Pete re-work it with his CNC program. No change.
I installed a VMax velocity ring, no change.
I changed EOIT to spray later, after the exh valve shut. This did not help the miss, but did help the idle fuel smell.
I have moved injectors around a couple times, during all the intake manifold and head work. The misfire events seam to occur more frequently (according to the logs) with the four center cylinders than the outer four. I have to admit though, I have not actually took note of which injector got moved around. So I suppose, it is possible that I have reinstalled the injectors in the same holes each time, possibly….
I’m running out of things to change. The injectors I’m running are from FIC. They are new Bosch, 60 pound LS7 injectors.. They were supplied with all the data for the injector tables and I have verified that I input the data correctly. I’m at a loss what else to look at, other than possibly the injectors themselves.
If I’m going to buy new injectors, again, I figured I’d try these ID’s, as sooooo many people think they are the best thing since sliced bread.
What is so different from the ID’s than any other brand? If you have the correct data for the tune, what makes these so much better, and also, so much more expensive?
I am hitting about 67% duty cycle with the 60’s. I do not know how to interpret the flow rates on the ID’s. Would the 725’s be the size I need, based on the duty cycle I am seeing with the 60 pound Bosch injectors?
I have a FAST 102 and am using the LS2 fuel rail and injector spacers. (I have also swapped out the FAST spacers with spacers that go between the injector and the rail, with no improvement either). Which injector do I want to get that would allow me to get rid of the spacers? LS2 injectors?
And lastly, is there something else I should check before screwing around with the injectors?
The car is going into storage here real soon. I have a couple months to ponder this. I’d like to have a game plan and parts on hand before I get the car back out of storage, so I can actually drive the damn thing for once. It’s either that or I’m buying a viper, and leaving it STOCK!
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Originally Posted by Michael_D
