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grillhands

L28e turbo conversion shuts off after 8psi

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I've been driving my conversion for a few months now at 5 psi with no problems. My a/f stays around 11.1-11.6. I bumped the boost to 8psi and the car will turn off like it's not getting fuel. For me to be able to start it again I would pop the hood with the key on and manual prime the fuel lines by moving the flap by hand. Sometimes I can't hear the fuel coming in so I would have to do it twice or more. I have all stock l28e components. My initial thoughts is fuel pump but I don't see the a/f creeping up when it happens. Could be possible that I'm outflowing the afm? I do have the l28et afm handy and a spare l28e afm that I could try. Any suggestions would be great. Thanks

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The AFM is out of the equation doing nothing once you are WOT and on boost over about 3,000 rpms.

 

It is only active in part-throttle  situations and lower RPM's. The stock N/A's "outflow the AFM" at aroudn 3,500 when the box goes to a preprogrammed fueling curve. 

 

it's not a MAF sensor, it is NOT active through the whole load scalar range of the engine giving source feedback for the fueling of the engine.

 

It opens, the ECU/ECCS is "open loop" and on a preprogrammed curve.

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Ok. Thanks Tony. I'm gonna fiddle around a little more to see what the issue could be. I plan on replacing the fuel pump because I think it's the original from 75. The car only has 90k and by the looks of the pump I would bet it was never replaced.

Edited by grillhands

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Partial throttle or wot it doesn't matter.The rpms are around 4.5-5k and it's a complete loss of power. I usually set myself up on a dead road so when it turns off I won't affect traffic. The only way I can get the car to start again is to manually move the afm flap until the fuel pressure builds back up in the system. Once I do this the car is fine. There are no signs of sputtering or misfiring. It turns off abruptly.

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If you drop the boost back to 5 the problem disappears?  Might just be coincidence.

 

If you have a manual transmission, watch the tach when it dies.  If you're still in gear with the key on the tach should still show spark when rolling.  If the tach drops to zero while rolling, that would be a sign of an igntion problem, maybe with, maybe without, a fueling problem.

 

Also, you said L28E, not ET, for engine management.  Is this a cobbled together turbo setup?

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Like was previously mentioned, the stock l28et manifold has an emergency pop-off valve which will vent excess boost pressure at a certain point. Enough that I removed mine in order to run an 8 psi spring. It was a while ago, but I know that I removed it because it would have caused issues at 8 psi if I left it on. It basically creates a boost leak, which would make the car lose power and stumble until the pressure goes back down.

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The Emergency Relief Valve should pop at 10psi, and if you wire your wastegate shut it will lift on a stock turbo and run you along happily at 10psi all day long.

 

Which is, incidentally, where the stock ECCS Mapping ends... Which is why when you take a stock ECCS and start cranking up boost (with the ERV Plugged) it will not make any more power after 10 psi and start running progressively leaner. At 10psi the stock ECCS is around 14:1 at 5,000 rpms....which is fine, but....

 

At only 8psi it will not make you slow down and stop as described. I would still plug it, but I doubt the issue is the ERV. I wired my wastegate shut on my 84 Skyline and ran it on the ERV for about two weeks to see if bad things would happen. It survived. Then I sold it to a guy from WV. He seemed to enjoy the stock boost. Meh.

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I'll take a look at the tach next time to see what it's doing. My setup is stock l28et manifold with turbo, front mount intercooler, locked n/a distributor at 28 degrees. I also have a spa fmu with a adjustable range of 1:1 to 12:1. I have to double check to where I set it

 

I don't think that this is your immediate problem, but the stock fuel pump has an internal pressure relief that I believe was set to ~55psi for non-turbos.  So your rising rate FPR likely won't add nearly as much fuel as you might expect.  

 

For instance, as I recall your stock base fuel pressure is 37psi, and as Tony pointed out the ECCS mapping ends at 10 psi boost, at which point your "normal" fuel pressure would be 47psi.  Fuel flow increases with the square root of pressure, so the most additional fuel you'll be able to add will be about 8% over what was available at 10psi.  If you want to use the FMU as intended you really need to go to a pump that can supply the additional fuel at the pressures you'll require.  It might not be your immediate problem, but it will be soon...

Edited by TimZ

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Fixed the problem. I got a new afm harness because apparently the vibration at higher rpms would rattle the connection just enough to cut fuel. I bought a new 7 pin connector on ebay and now the car runs, idles and boosts much better. Fuel pump is still going in soon. I didn't want to just throw parts at it lol

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