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540 troubleshooting MAP vs. mechanical gauge
Hi, Trying to troubleshoot a recently purchased 540. Problem is a backfire through intake while applying throttle under load from idle to roughly 1800 RPM. Seems like the motor is lean at this point. And was thinking Vacuum leak. I have an O2 sensor but also have some reversion so do not trust the reading at or around idle, but it does indicate LEAN condition during this RPM range. MEFI-3 ECM. Cam profile 240/248 .621/.632 112 LSA. 4500 FAST throttle body. Stock GM heads MAP at idle reads about 21 inches and 3.2 volts, however a mechanical gauge reads 8-10 inches. Should the vacuum readings match or has the MAP value been programmed into the ECM? Thanks for any advice. |
Have you checked the timing
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Originally Posted by F-2 Speedy
(Post 4709000)
Have you checked the timing
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Did this just start ?
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Who programmed it ? has this always happened from new or just started, fuel pressure @ idle and accelerating
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Did you try another Map sensor ?
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Originally Posted by GPM
(Post 4709050)
Did you try another Map sensor ?
I set up the fuel system. A1000 at 40 psi at idle and holds while accelerating. Fuel system set up exactly to Aeromotive specs. Have tried moving up on regulated pressure. 45, 50, 55, etc.... Compression readings and leakdown results all good. Yes I have tried another known good MAP sensor. Same readings on different MAP sensor. The ECM was programmed by Innovation Marine. I have also tried another ECM with an ASM tune. (540 with 525 EFI cam) It seems to work better with this computer on it but ultimately still have the backfire through intake. Does anyone know if the MAP reading/voltage is programmed into the ECM or should this be an organic reading created by vacuum conditions of the motor. Thanks |
The Map sensor tells the ECM how much load is on the motor, which determines the injector pulse width, basically the fuel. One of your readings is wrong, I'm betting on the Map sensor with that much cam. You need a tuning program with data logging and a laptop so you can adjust the VE table.
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It is likely lean. But....do you have the correct MAP sensor? i.e. a 1 Bar sensor and not a 2 Bar?
If your motor is indicating lean try solve that issue first. I don't care if you think you have reversion, put some fuel into the lean spot and see what happens. Trust the wide band until proven otherwise. |
Originally Posted by GPM
(Post 4709221)
The Map sensor tells the ECM how much load is on the motor, which determines the injector pulse width, basically the fuel. One of your readings is wrong, I'm betting on the Map sensor with that much cam. You need a tuning program with data logging and a laptop so you can adjust the VE table.
Looking at the MAP sensor vacuum reading on a Rinda, should MAP vacuum and the mechanical gauge vacuum match pretty closely? |
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