Has anyone ever had a weird engine rpm reading on the dyno ?
- Thread starter SVTsamson22
- Start date
Well it'd help if you didn't cut off the RPM scale on the bottom... quick look it goes rich right before 5k (only visible number) and lean at the division before that 4-4.5k? I'm guessing this is a returnless system? Fuel system info would be helpful.
Data logging is a good place to start. Check if there is anything strange going in that RPM range with MAF counts, voltage, fuel pressure, etc. The problem only appears in a narrow band in the middle of the RPM range, makes me think it's a tuning issue.
Is it possible for belt slip to cause something like that ?
The A/F spikes lean right at the start of the bobble....it's going to be tune/fuel delivery issue. Log it to pin point further.
Boost seems rock solid so I'm going to say no. Looks like the pumps start to fall short then the computer over compensates. Common with returnless if not tuned perfect due to the PID controls. You can see it go a touch rich, overshoot lean, over shoot again bad to rich. You know which side of the FPDM the boost a pump is on? If it's after it tends to amplify any misstep the computer makes. Someone like @decipha will have better insight. My guess is tune.
I'd log voltage, maf counts, fuel pump duty, rpm, load, pressure drop across injectors, throttle position. Your pretty up there for stock pumps and a boost a pump.
Last edited:
The pump a boost and fuel pressure module is on driver side I just switched out the fpdm for a new one and put in a new ford motorcraft battery because I was getting low voltage at WOT I'm thinking of going return style and getting rid of the return less to save me the trouble of praying everytime I send it she don't give out on me and the motor goes boom.
I meant before or after the FPDM you can wire is pre or post. I'm a return fan but might be able to just get slightly bigger pumps and ditch the boost a pump and get away with it. Kind of reaching the limit of my knowledge though. Hopefully one of the gurus show up, Kevin who tuned C6zhombre's car is one of the few people I've seen get a nice high volume returnless system working well. Can never remember his tag, he's a mod in the tuning section.
Thanks for the info. What's a good return style set up to go with in your Opinion ?
I love my new Fore setup, very nice pieces but they should be for the price. A lot of Division X guys seem happy too. I'm sure there are more options I don't know about just always like Fore so just went with that and didnt look around too much.
Way back in the day when I ran a BAP, same thing, mine would just cut out at 4k. You should run the BAP before the FPDM. The computer can control it better. Also run the BAP full on all the time. Dont use the Hobbs switch.
Hook the BAP into the brown w/pink wire in the FPDM harness.
My tuner wired mine this way and was back to making full pulls again. You might be close to maxing out the stock pumps at 600 rwhp. So start looking into a return style anyway.
Double.
That's how I set mine up before I switched to e85. Definitely the way to go.
Users who are viewing this thread
