325es swapped to m20b25 not getting enough fuel?

[Joev253]

Hey guys I swapped a m20b25 into my 325es and it idles perfect but when you give it a lot of throttle it's starving for gas.. I'm not really sure what it could be.. Are the injectors on an m20b25 bigger which would require be have a bigger fuel pump? Just really could use some help

[E30_Pare]

Does it stutter up top or do you get a hard fuel cut off? If anything i'd start with a new fuel filter since those seem to be commonly overlooked.


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[matthugie]

The fuel delivery system is perfectly sufficient unless you have a dying pump. I suppose if your external pump was dead the low pressure in tank could supply enough to idle but not enough to completely run. However, if the swap hasn't run otherwise then I'd be inclined to say you have an issue under the hood.

[Regnar75]

when you did the swap did you upgrade to motronic 1.3? IIRC the motronic 1.0 eta injectors are low impedance and the m20b25 injectors are high impedance, i dont know for sure if this would cause the issue you have but i dont think running ETA injectors on a b25 is recommended. also the ETA uses a 2.5bar FPR while the b25 uses a 3.0bar FPR, if your going to m20b25 i would use the whole engine management system (fuel air spark) in the swap.

[E30_Pare]

The fuel delivery system is perfectly sufficient unless you have a dying pump. I suppose if your external pump was dead the low pressure in tank could supply enough to idle but not enough to completely run. However, if the swap hasn't run otherwise then I'd be inclined to say you have an issue under the hood.

When my inline pump died the intank pump over compensated with a 3k rpm idle.


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[Joev253]

It idles fine and if you dont go real fast when you rev it up really high it's fine it's only when you go fast it like kinda cuts out gets sputtery then go normal for sec then sputtery again. I realized I am using the afm from my eta motor so I'm gonna swap that out tomorrow and see could that be it?

[blue plates]

Check timing?

[anokES]

It could be ignition as well, so you might be having a misfire. Change all your spark plugs, and if that doesn't work check your ignition wires and your distributor cap

[cabin]

It idles fine and if you dont go real fast when you rev it up really high it's fine it's only when you go fast it like kinda cuts out gets sputtery then go normal for sec then sputtery again. I realized I am using the afm from my eta motor so I'm gonna swap that out tomorrow and see could that be it?

Could definitely be the AFM. You need to be using the AFM from an m20b25, the eta AFM will not work.

[jlevie]

It idles fine and if you dont go real fast when you rev it up really high it's fine it's only when you go fast it like kinda cuts out gets sputtery then go normal for sec then sputtery again. I realized I am using the afm from my eta motor so I'm gonna swap that out tomorrow and see could that be it?

I'm surprised that it runs as well as it does with the ETA AFM. You must have (as noted) the M20B25 AFM. And the rest of the M20B25 parts (intake, injectors, FPR, engine harness, CPS, and DME).

There could be a problem with the fuel delivery system. Tee a gauge into the rail supply line and see what the pressure is when the engine misbehaves. You can zip tie the gauge to a wiper to be able to see it while driving. Above idle rail pressure should be 43-45psi. A bad FPR, clogged filter, weak high pressure pump, dead transfer pump, or rust in the tank are all possibilities for low rail pressure.

[efficient]

Lol my eta afm made my car run like shit as soon as I swapped in my I afm it worked good

[Yogawrench]

I just did an "E" to "I" swap on a 1988 Super Eta. Did you swap in a higher fuse (30 amp) for the fuel pump? (It's fuse #11 in the panel.) I think the ETA has a 7.5 amp fuse in there.

[jlevie]

I just did an "E" to "I" swap on a 1988 Super Eta. Did you swap in a higher fuse (30 amp) for the fuel pump? (It's fuse #11 in the panel.) I think the ETA has a 7.5 amp fuse in there.

The fuel pump(s) on either variant are the same and draw just a few amps. It is neither necessary nor desirable to use a bigger fuse.

Understand that a fuse (or circuit breaker) is sized to protect the wiring, which in turn is sized to handle the load. Increasing the fuse size without upgrading the wiring can lead to electrical fires.

[Yogawrench]

The Bentley manual shows the fuel pump circuit (#11) requiring a 15 amp fuse for post 1988 cars, and 7.5 for "E" cars. So for the "I" swap we should just stay at 15 amps?

[jlevie]

The Bentley manual shows the fuel pump circuit (#11) requiring a 15 amp fuse for post 1988 cars, and 7.5 for "E" cars. So for the "I" swap we should just stay at 15 amps?

That is a reflection of the change in the fuel tank and pump. From 9/87 on the cars had a 63L tank with a single in-tank high pressure pump, which draws slightly more current than the dual pump system used in the earlier cars with the 53L tank. So the correct fuse is the one that matches the car's configuration, regardless of what engine is used.