david scitern Posted September 12, 2021 Share Posted September 12, 2021 hi all. i have a 1991 reatta. have changed a broken o2 sensor, installed missing cam sensor magnate, replaced leaking intake gaskets, replaced idle control motor, new mass air flow sensor, new ecm, new ignition module; fuel psi is 47. have power flushed injectors and tuned-up. ive been a drivability tech since 1983 and have to say my own car is whipping my hinny!!!! lol. the problem does go away when i unplug the mass air flow meter. all wiring is good and have tried yet a second maf sensor??? it acts like a calibration problem: has a eprom # AWAC in it. does anyone know if this is correct? any info will be much appreciated. Link to comment Share on other sites More sharing options...
Padgett Posted September 12, 2021 Share Posted September 12, 2021 That is strange, I show the 4214/AWAC as for a '91 L27 3800 with a manual transmission.ECM is 16137944. Does it lockup in 4th over 50 mph ? What I show for a 91 Reatta is 6748/AWRH (Fed) or 6743/AWRF (Cal). I do not have a .bin for either. Note: the L27 is different from the LN3 and has a larger MAF. Does have the good Delco ignition. Link to comment Share on other sites More sharing options...
Ronnie Posted September 12, 2021 Share Posted September 12, 2021 If surging while driving and your foot is on the gas, that takes the IAC out of the picture. Sounds like raw air is entering the engine that isn't going through the MAF if the engine is surging (not missing) when holding the throttle steady. You should check the part number for the MAF to make sure it is the correct one. I don't think the '91 is the same as other models. If the engine surge feels like all cylinders are losing power and then picking right back up that is another story. Have you done the fuel pump stress test in the How-To guides here on ROJ to determine if the pump can maintain constant pressure? I would start by plugging all the vacuum ports on the engine, including the brake booster,and see if that changes the way it runs. Link to comment Share on other sites More sharing options...
david scitern Posted September 12, 2021 Topic Author Share Posted September 12, 2021 Padgett it does have ecm# 1613944. humm, do you know the maf part number to match the ecm/eprom combo; sound like worth trying rather than hunting down the proper combo....and yes it does have tcc lockup. the rolling adle and surgeing are the only concerns present. Link to comment Share on other sites More sharing options...
david scitern Posted September 12, 2021 Topic Author Share Posted September 12, 2021 yes ronnie have been through all thre basics many times, but thanks much for info. age has taught me well how easy it is to over look things no matter how high experience level a person may have....lol!!! Link to comment Share on other sites More sharing options...
2seater Posted September 12, 2021 Share Posted September 12, 2021 (edited) I can't find my photo of the different MAF sensors but does the sensor that was replaced have a plastic cover that surrounds the sensor wires so they appear to be in the center of a round hole or are the sensor wires just out in the open when removed from the throttle body? Either style will fit the housing but only the sensor with the surround is correct for the one piece Hitachi throttle body and MAF. What does the MAF signal do while this rolling idle is occurring? Edited September 12, 2021 by 2seater Link to comment Share on other sites More sharing options...
Padgett Posted September 12, 2021 Share Posted September 12, 2021 Well, I'd start with the basics: what are the idle command, TPS, knock sensor (oldPA3), O2, and fuel trims doing. Is hard to tell from all of the changes made but, I suspect a vacuum leak (since no MAP have to add a gauge). Do you have lockup in 4th above 50mph or not ? Link to comment Share on other sites More sharing options...
david scitern Posted September 12, 2021 Topic Author Share Posted September 12, 2021 yes i have convertor lockup 50mph and up Link to comment Share on other sites More sharing options...
Padgett Posted September 12, 2021 Share Posted September 12, 2021 OK then you have the proper PROM for an automagic. My listing may be rong. Link to comment Share on other sites More sharing options...
david scitern Posted September 16, 2021 Topic Author Share Posted September 16, 2021 got the car fixed, youll will love this!!!! i installed a reducer shim into the maf sensor air supple port, reduding it 1/16 of an inch........all problems are gone. man that car will go now, lol! Link to comment Share on other sites More sharing options...
david scitern Posted September 16, 2021 Topic Author Share Posted September 16, 2021 no dought it was a calibration issue: thats for all youlls input :) Link to comment Share on other sites More sharing options...
2seater Posted September 16, 2021 Share Posted September 16, 2021 Can you add a photo of what the modification is? I have fooled with the MAF's for both the LN3 and L27, adapting both types to the opposite engine as part of my turbocharging experiments. I have seen the MAF signal bounce around at lower rpms, my assumption is turbulence in the intake manifold when close coupled, so I am truly interested. Link to comment Share on other sites More sharing options...
Ronnie Posted September 16, 2021 Share Posted September 16, 2021 1 hour ago, david scitern said: got the car fixed, youll will love this!!!! i installed a reducer shim into the maf sensor air supple port, reduding it 1/16 of an inch........all problems are gone. man that car will go now, lol! By doing that and it making the engine run right you must be compensating for something else that is out of whack. Most likely unmetered raw air or O2 sensor problem. 1 Link to comment Share on other sites More sharing options...
david scitern Posted September 17, 2021 Topic Author Share Posted September 17, 2021 no raw air ronnie and two different brands of O2 senors have been tried. 2seater i will for sure supply you with a picture this weekend. you can also install a varible resistor on the signal return wire and calibrate it. i will be going to that method soon as to gain varible control......fun!!! Link to comment Share on other sites More sharing options...
Ronnie Posted September 17, 2021 Share Posted September 17, 2021 1 hour ago, david scitern said: no raw air ronnie and two different brands of O2 senors have been tried. If that is the case how could the need to modify the air flow to the MAF be explained? Link to comment Share on other sites More sharing options...
Padgett Posted September 17, 2021 Share Posted September 17, 2021 I'd be putting in a tablet displaying many parameters, CRT only displays one at a time and does not log. Moates.net has everything you need. 1 Link to comment Share on other sites More sharing options...
2seater Posted September 17, 2021 Share Posted September 17, 2021 The MAF uses a frequency up through 10.4kHz, not a typical variable voltage, so I am not sure how it could be tuned? Granted the scale in the EEPROM can be moved around some but the ECM still only has a fixed upper frequency limit as far as I am aware. That is something I need to work on myself as I am using a 3"inline MAF from a Chevy engine I believe. It uses the same frequency range but flows ~50% more air at the same frequency so I don't run out of range in the present turbocharged iteration. Was that a typo on the different O2 sensors? That doesn't have anything to do with air flow that I am aware of. 1 Link to comment Share on other sites More sharing options...
Padgett Posted September 17, 2021 Share Posted September 17, 2021 L27 has a larger capacity MAF than a LN3. Link to comment Share on other sites More sharing options...
Philbo Posted September 17, 2021 Share Posted September 17, 2021 @david scitern Out of curisity did you replace just the MAF sensor itself or the whole MAF assembly? I happened to notice in my manual when I was doing my intake gasket that it says the sensor and the aluminum housing is a matched set. I wonder if that had anything to do with the issue. Link to comment Share on other sites More sharing options...
Ronnie Posted September 17, 2021 Share Posted September 17, 2021 14 minutes ago, Philbo said: I happened to notice in my manual when I was doing my intake gasket that it says the sensor and the aluminum housing is a matched set. Good info. I didn't know that. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now