S52 swap fuel pressure question / fuel trim

[ilillund83]

Hey all, my s52 is in and runs great but I had a quick question. I did not replace the fuel pressure regulator or the fuel pump (3bar vs 3.5). Should I? I would not worry about it except I am having a hard time passing CA smog due to high hydrocarbons only at idle.

It seems to me that if it were a low fuel pressure issue I would notice problems higher in rpm and under load in general. On the other hand I thought that it could also be caused by the computer opening the injectors longer to compensate for the lower overall pressure and the fuel trims not reacting fast enough when rpm drops to idle and dumping more fuel than needed causing the high HC issue. ( I might be WAY off on this and could use guidance! )

Thus far I have smoke tested the vacuum system, replaced all injectors, new o2's, new coils and plugs, and quite a few other things but no dice. The computer is clean, all monitors are ready with no faults and the car seems to run flawlessly.

One last bit of info, My long term fuel trims on bank 1 and 2 are +11.7 ( My assumption was this is also caused by the 3bar pressure regulator but again I may be off base here )

Sorry for the long read just trying to get info out there, any and all suggestions would be appreciated!

[ilillund83]

For anyone who comes across this thread in the future, It was indeed the fuel pressure regulator causing my issue. If you do a 6cyl swap this must be changed out as well. It will run and seem normal with the stock ti regulator but the computer has to compensate and can cause issues with trims when returning to idle.

[J!m]

I just saw this but I’ve been running my swap since about 2001 and never ran across this issue.

At first the car was checked at the pipe and within new car tolerance (for a 328 even, not a 3.2 liter) and since been plugged in to the dme to check more recently.

The fuel filter should be new/clean when you do the swap. 1/2 bar is like 7 PSI so that difference is increased with the restriction of a bad/dirty fuel filter.

Good to have this documented but I don’t think this was the root cause. I was going to suggest the secondary air pump efficiency is poor, if the emission check was on a cold engine.

The other thing to do is run it to 1/4 tank and add two cans of “dry gas” which they may not even sell in warm CA. That will clean it up. Also be sure your air filter is NOT an oiled type, and that it is clean or removed for testing.

Keep us posted on other developments.

[ilillund83]

Hey J!M, thanks for the heads up. Yeah I changed the fuel filter when changing the regulator so it very well could have been that my filter was slowing down flow, 3 years old or so. Just glad to have it sorted.
Last night I did the instrument cluster swap and everything works properly except the fuel gauge shows completely empty/light on. I saw on realoem that the compacts used a different level sending unit than all other e36's. Did you have to change this when doing your swap? Thanks!

[J!m]

No issue with the fuel gage. You have to add a wire for the fuel economy gage to work, that’s it. You may have bent a pin or something.

[ilillund83]

Must have been getting tired when I installed the cluster. I pulled it back out and found part of the retaining clip had broken and was keeping the plug from fully seating . All is well!

[J!m]

Yeah those clips were crap when new. Now they’re over 20 years of old...