Need some opinions

S

slow94

Well-known member
So most know I have swapped to a new built 427. For the most part things have gone well but what I'm running into now is a misfire problem. It seems to happen over 5000 rpm and is hit or miss up to the shift at 7000 rpm. So far I have swapped plug wires back to my old set with no change. Put new 7 range plugs instead of 8 range plugs I started with.. no change and the 8 range plugs looks great. Posted on stinger forum and they suggested I change up my grounds to my coil harness (ign1a coils) so I re did those without change. They said the harness they sold me should have been done differently power wise so I redid the power side to better distribute power with no change. Air fuel ratio is low 13's high 12's with 30 degrees timing (E85) generally when it happens so that should be good. It is only at somewhat higher rpms that it happens. All other situations it works fine. I thought it could be injector related but it's not a constant miss and is only at higher rpm and it isn't always perfectly consistent ( I still may send them off to be cleaned). Rpm is saying it is "synced" throughout entire run. This is all first gear testing right now but I may try a 2nd gear pull tomorrow to see. Anything you guys would test?

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FlatOut said:
same ignition and tune parameters as before? Valves adjustment maybe?
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Yep same ignition and tune has only been changed to accommodate the larger engine and target A/F ratio. I asked engine builder about the valves but like me he believes it would be less than 1% chance it could be float. New motor is solid roller cam with springs that are built for boost. NA should be a cake walk for this motor mechanically. Not ruling it out but it's not top of list.

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Can you post your data logs?

There's all kinds of crazy stuff it could be. I've learned what most of the status messages mean and that makes the logs much easier to interpret.
 
Here are a couple... Its not always super clear on the logs but can see short lean spikes when it misfires. Unfortunately, this is just the passenger bank A/F.
 

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slow94 said:
Here are a couple... Its not always super clear on the logs but can see short lean spikes when it misfires. Unfortunately, this is just the passenger bank A/F.
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What dwell are you running? Also when you wired the IGNs you grounded to the head as well as the main ground right? Then used sensor ground?
 
Raymond_B said:
What dwell are you running? Also when you wired the IGNs you grounded to the head as well as the main ground right? Then used sensor ground?
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Dwell was set at 4.0 ms but it was like that before handling 20+ psi boost. The harness came direct from stinger. Before I literally had the coils grounded to my intake and all worked. I have since tied the 8 coil grounds to the driver head and put a 2 gauge jumper wire from there to passenger head. The other grounds for coils I have going to same spot my battery negative bolts to frame. The sensor ground is on firewall and from my understanding isn't as crucial as the others. Stinger has admitted that the company that built their harness didnt exactly do a great job. However my truck never misfired before.

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slow94 said:
Dwell was set at 4.0 ms but it was like that before handling 20+ psi boost. The harness came direct from stinger. Before I literally had the coils grounded to my intake and all worked. I have since tied the 8 coil grounds to the driver head and put a 2 gauge jumper wire from there to passenger head. The other grounds for coils I have going to same spot my battery negative bolts to frame. The sensor ground is on firewall and from my understanding isn't as crucial as the others. Stinger has admitted that the company that built their harness didnt exactly do a great job. However my truck never misfired before.

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Click to expand...

Interesting, when I bought my coils from DIY Autotune they recommended no more than 3ms dwell. So that's what I run, obviously cranking is higher, but that's a short amount of time.

I built my harness as 2 banks of 4 and 10AWG power and main ground on each bank. Then 10AWG going to the back of each head for that ground. Sensor ground is a star lug and dedicated to only sensor grounds.


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From what I understand you can run up to like 7-8 of dwell for very short periods of time but general consensus is 5 ms is about the limit. Stinger recommends trying a lower dwell setting temporarily.. less dwell will help with wiring issues somewhat. Each bank of coils on mine is powered by a 16 gauge wire which they say is enough. I mean it was enogh before I suppose, and old motor was making 400-500 more HP than this one currently is.

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slow94 said:
From what I understand you can run up to like 7-8 of dwell for very short periods of time but general consensus is 5 ms is about the limit. Stinger recommends trying a lower dwell setting temporarily.. less dwell will help with wiring issues somewhat. Each bank of coils on mine is powered by a 16 gauge wire which they say is enough. I mean it was enogh before I suppose, and old motor was making 400-500 more HP than this one currently is.

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Click to expand...

When I was building my harness I looked at the Holley "smart coil" (which are IGN1) harnesses. In the instructions they recommended over a certain dwell and RPM to upgrade the harness wiring guage. That was all I needed to see, it showed me that these coils can draw a lot of amps and if I was building a harness why not ensure there would be no issues? I think DIY also sells a larger gauge kit for the coils too :) Not saying any of this is your issue, but at the power levels you're going to make there's no way I'd run 16ga.
 
Oh BTW, yeah your log looks clean, you can see the misfire, but no indicators that anything is wrong. Where is fuel pressure being logged? Did I miss it?
 
What was your shift rom before. I would think the 16ga is the problem under high rpm load.


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ASAP said:
What was your shift rom before. I would think the 16ga is the problem under high rpm load.


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Shifts before were at 6000-6200. But the truck starts breaking up now around 5000 rpm. I'm thinking max rpm for new motor will be 7500 but likely be under that.

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I'm puzzled by the system working fine with the old motor with boost, but it messing up with the new motor naturally aspirated.
 
FMOS Racing said:
I'm puzzled by the system working fine with the old motor with boost, but it messing up with the new motor naturally aspirated.
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Me too. I lowered the dwell and it improved maybe a tiny bit but still misfires. I have a new set of coils being delivered tomorrow so that is my next step. Maybe I have a coil going bad. If that doesn't do it I will remove the entire harness and inspect all wires and send injectors off for inspection as preventative maintenance.

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slow94 said:
Me too. I lowered the dwell and it improved maybe a tiny bit but still misfires. I have a new set of coils being delivered tomorrow so that is my next step. Maybe I have a coil going bad. If that doesn't do it I will remove the entire harness and inspect all wires and send injectors off for inspection as preventative maintenance.

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Click to expand...

What plug gap are you running? And what do the plugs look like?
 
Hearing your description made me think of two things: point bounce and spark scatter. I think we can safely rule out the first one, and I can't remember the last time the second one came up. If the ignition is all the same as before, the distributor should be OK. But should is also one of my least favorite words lately. What about the oil pump and oil pump drive shaft? Anything new, different, or out of the ordinary with those? Do you have an old fashioned dwell meter you could hook up to a coil and check the dwell to see if it agrees with what you've set it to? Will an old school dwell meter even work with a CNP system? Does your EFI system require the cam sensor you've got to run, or could you drop a cheap distributor in just to see if it changes anything?
 
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