MAF/injectors and now car is running like garbage. Help!

[ksizzler]

I recently rebuilt an M20B25 and swapped out my M20B20. I have a 173 ecu. I had everything in as stock and it was running strong once i found all the vacuum leaks and minor issues (engine temp sensor, TPS out of adjustment). I purchased a 2.7" miller maf conversion (Gen III) from Ireland Engineering(installed chip in correct orientation and soldered the correct wires). I also upgraded to 17.5lb green top bosch injectors added an adjustable FPR to bump fuel pressure up to compensate for the larger injectors (tried a range of pressures from 35psi up to 60 psi and the stock 43psi). Settled at 50psi as it at least gets me to work and back. Once said items were installed the car started running like garbage. Idle is at about 1300rpm at all times and will ocasionally drop to 750ish and then right back up, soon as i touch the accelerator to move, to 1100-1300rpm. It hesitates and bucks through the rpm range up until it hits about 4k. The engine barely can pull the car up a hill at 4k in second gear. Also the engine really loses power and bogs at WOT. It will pulls harder at 3/4 throttle than it does at WOT. I'm at a lose of idea. I've followed the maintenance manual and tested every possible cause of erratic/high/low idle and everything checks out within limits. every relay and fuse has been tested and is the correct one for perscribed position. I've pulled the ECU and checked perscribed pins at the ECU connector in accordance with the manual. Now my question is what the hell is going on. I'm about ready to push this car faster off a cliff. Does the ECU lose its adaptability when the MAF/chip is installed? Is the MAF/chip combo not accepting the larger injectors? the only thing i havent done was revert the injectors back to the stock 14lb. I'll be doing that tonight. If anyone has experience or has had a similar problem please chime in and let me know what you have checked or what your fix was.
Sorry about the novel and dryness. just wanted to be detailed as possible on the issue.

[downforce22]

I had some driveability issues like this. Are you sure you don't have a vacuum leak? Is the car missing on a cylinder or firing on 6? Those were my problems, one cylinder's spark plug was fouled. With larger injectors and higher fuel pressures you are probably running rich. Maybe lower fuel pressure closer to stock 3 bar?

Was the car running right before the maf? I would think it would be pretty easy to remove the chip back to stock, and replace the maf with the afm to see if that helps. Obviously you soldered a wire, was it the right one? Can you reverse it to try unning with the afm?

[Denny]

I recently rebuilt an M20B25 and swapped out my M20B20. I have a 173 ecu. I had everything in as stock and it was running strong once i found all the vacuum leaks and minor issues (engine temp sensor, TPS out of adjustment). I purchased a 2.7" miller maf conversion (Gen III) from Ireland Engineering(installed chip in correct orientation and soldered the correct wires). I also upgraded to 17.5lb green top bosch injectors added an adjustable FPR to bump fuel pressure up to compensate for the larger injectors (tried a range of pressures from 35psi up to 60 psi and the stock 43psi). Settled at 50psi as it at least gets me to work and back. Once said items were installed the car started running like garbage. Idle is at about 1300rpm at all times and will ocasionally drop to 750ish and then right back up, soon as i touch the accelerator to move, to 1100-1300rpm. It hesitates and bucks through the rpm range up until it hits about 4k. The engine barely can pull the car up a hill at 4k in second gear. Also the engine really loses power and bogs at WOT. It will pulls harder at 3/4 throttle than it does at WOT. I'm at a lose of idea. I've followed the maintenance manual and tested every possible cause of erratic/high/low idle and everything checks out within limits. every relay and fuse has been tested and is the correct one for perscribed position. I've pulled the ECU and checked perscribed pins at the ECU connector in accordance with the manual. Now my question is what the hell is going on. I'm about ready to push this car faster off a cliff. Does the ECU lose its adaptability when the MAF/chip is installed? Is the MAF/chip combo not accepting the larger injectors? the only thing i havent done was revert the injectors back to the stock 14lb. I'll be doing that tonight. If anyone has experience or has had a similar problem please chime in and let me know what you have checked or what your fix was.
Sorry about the novel and dryness. just wanted to be detailed as possible on the issue.

OK I can tell help you.

I can tell you right now that the problem is your running rich.

Basically your car fuel pressure to start should NOT be raised it should be at stock 42PSI always.

Bigger injectors mean you have to scale down the fuel (do you have the Miller WAR chip or just a normal burned chip?)

Let me know...

[barry]

Ok so I have the same problem, I'm going to have it smoke tested, The only thing I haven't changed are the spark wires, I run 19lb injectors and a Bosch MAF and the miller base chip, when I first installed the miller system the car ran really well except for the idle was about 1200. I keep reading about certain things that cause non starting, rough idle etc. these cars are old and when you change or add something I think you need to make sure its done right. So i'm going to take my car to a older BMW mechanic with the right software and knowledge to get the car tuned properly.

[ksizzler]

The car was running tits prior to the MAF on the larger injectors. No WAR chip just the one supplied with the MAF. I read over the miller installation manual more times than i could count prior to doing a thing. I know for a fact i did it correctly and a my buddy was sitting right there watching me do it and agreed it was correct. So basically tonight i swapped back to the stock injectors. I dropped the fuel pressure back down to 3bar/43psi. Now the car will start and idle rough as hell and is beyond rich. Idle is about 750. Trying to move the thing is out of the question. I put all new plugs, new wire set, cap and rotor before the engine went in. I'm not 100% positive on zero vacuum leaks. I did check every spot i read about in other threads andand used a little ether on all the potential leaks and found nothing. I'll have to look into getting a smoke test done once its running to be sure. I'll check the plugs tomorrow just to be sure and if they are all kosher i'm just going to revert everything back to stock and see what happens. It shouldnt be too hard to undo the maf and solder. I'll keep you guys posted on the results. Thanks for droppin some knowledge!

[jlevie]

Okay, ditch the MAF and revert the car back to the stock chip and AFM. If it runs fine then there could be a problem with the MAF, the chip, or installation.

[Denny]

At this point good idea on removing the spark plugs as they are probably soaked. when I was having a similar problem I also checked the compression on the engine at the same time I cranked to rinse it out...its always good to check anyways.

My problem ended up being the connection grey wire to blue/red in the harness being loose but I could not hold an idle and you can.

revert back to stock if you can and have all the components to eliminate the MAF/CHIP from the equation.

[BMW_325i]

Is the MAF tune for stock injectors or 17-19lbs?

50 psi doesn't sound excessive if the green tops are M50 injectors which are 17.5lb/hr at 3.5 BAR (where stock pressure is 3 BAR).

I had the same setup and got best results at about 3.9BAR, no hesitation or flooding etc.

But after about 9 months i did change to injectors with same flow at lower pressure as i was concerned about stressing the fuel pump, given i don't know its age/history.

[E30-325iS]

Check that you have not plugged the MAF connector upside down. It is possible to fit it 180 Degrees out.

[ksizzler]

So an update on the issue. Maf is a gen three and has the tab so it only plugs in one way. I checked the cap rotor plug wires and plugs and all i found was that the plugs were a little dirty. I cleaned them up and reinstalled them and still the same issue. For shits and giggles i played with the fuel pressure again and found that the higher the pressure the better it ran. So (i know its stupid and not a good idea but) kept going up with the fuel pressure and at 70 psi the car ran perfect. This leads me to believe that the injectors are clogged and only at stupid high pressure is enough fuel getting through to let the engine run. I'll be sending the 17.5 lb injectors off to get them sonic cleaned and flow tested. Once i put some injectors in that are positively doing their job i'll give yall another update and let you know the outcome. Thanks again.

[BMW_325i]

It's also handy to have a wideband O2 / lambda sensor so you can see AFR's, takes some of the guesswork out.

[Aahj]

Just installed a Miller MAF conversion with the supplied chip with stock injectors and am having the same exact issue.

Car was running like a top before the install. Did you find a resolution to this issue? Anybody else have this problem?

Car runs extremely rich, black smoke out the exhaust and won't rev past 4500 rpm at WOT.

I have a 1987 325is with the 153 ECU

Thanks for any info you can provide!

AJ

[jlevie]

Are you sure that chip will work in a 153? If meant for a 173 (a safe guess) it won't be right for a 153.

[Aahj]

Yup, they even list it on their website. They offer the MAF conversion for the 153 ECU and it's written directly on the chip as well.

Just put it all back to stock and it runs like a champ. So either the chip or the MAF sensor is at fault.

Will call them tomorrow.