I'm having a problem finding information on testing a MAF sensor on a 1989 IROC-Z. Due to the cost of them I would like to test it before purchasing a new one. Would sure appreciate some info on the matter! The car I'm working on has no error codes stored in the ECM but won't start unless I prime it with gas then it runs terrible but it will run. I know better then to dump gas accross the MAF sensor so I know I have'nt ruined it yet this way. But the car has been worked on by other people and who knows what they have done. I bought this car from my little brother and it quit running around 3 years ago. He spent over $1200.00 having it worked on by other people (PROFESIONAL MECHANICS) and nobody could get it to run. They all said it needed a new wiring harness or it was shorted out in several locations and they would have alot of time and money invested ect... Well I've been working on cars for over 25 years and enjoy doing it so I bought it and decided I'm going to fix it myself. Well I took it home and after about 2 hours of trying to get it to run or do anything but give me erratic codes I decided to get back to the basics since the PROS couldn't seem to get it fixed with all the high tech stuff they had. Well long story short I checked the timing and they had it in 180 degrees off. As soon as I installed it properly all the erratic stuff corrected itself "who would figure". Well now after I put all the car back together after the last so called mechanic worked on it (it sat at his shop for over 3 months after which we had to go get it and haul it home all tore apart, wiring out of the harnesses, computer hanging by the wires ect... ) P.S he only charged $450.00 for his services!!! I think you all get the point. Anyway I have the car where it will start but it has to be helped to do so by priming it with gas. I have good fuel to it 43 LBS in the fuel rails, my noid lights flash properly when running. I've checked all the pinouts on the ECM for voltage and everything tests out. I,ve checked the TPS voltage is fine, Ect... Basically I've tested about everything and all tests fine but I can't find the info on how to test the MAF sensor with my volt tester, and I'm not the type of person to just throw parts at this car. Heck!!! thats what everyone else has been doing and it didn't work for my Brother. This car only has 60,200 miles on it and ran great before it quit 3 years ago. He was going down the Hiway and it just shut off. I believe that the ignition module is what actually was what went out that day. I had the old one that the original mechanic took out tested and it was bad. But I'm affraid that after the mechanic put the distributor back in 180 off he started probing and guessing and probully ruined some of the sensors. I've seen a MAF sensor go out before by people squirting fluid accross them and I'm thinking the PRO Mechanic did this. I can see what looks like squirt marks inside the intake. I would sure take any help I can get to figure this one out. When I prime it with fuel it will start right up, run good excellerate properly for about 7 or 8 seconds till the extra fuel in the runners is used up, Then it will just idle roughly. If I open the throttle it will start to rev up then run out of fuel and die and it will have to be primmed again to get it to start back up. If I don't touch the throttle it will stay running rough but not die. I've let it run for over 20 minutes and During this time the injectors are pulsing properly, the fuel rail is holding around 40 lbs of fuel pressure, no error codes are being created????? Please Help!!!!
Supreme Member
Can you datalog? That would be the easiest way. You could then see the maf voltage.
Heres something that might help. This is the calibration table from the 'vette ARAP prom. Shows the output voltage vs. flow. You should see around 7 or 8 grams/sec at idle with around 40-50 g/s when you blip the throttle. If it can do that then Id look elsewhere for the problem for now. One thing that can help is to gently clean the wires with a light solvent, althogh the stock mafs have screens at both ends, which woudl make getting to the wires hard.
Heres something that might help. This is the calibration table from the 'vette ARAP prom. Shows the output voltage vs. flow. You should see around 7 or 8 grams/sec at idle with around 40-50 g/s when you blip the throttle. If it can do that then Id look elsewhere for the problem for now. One thing that can help is to gently clean the wires with a light solvent, althogh the stock mafs have screens at both ends, which woudl make getting to the wires hard.
Code:
LC5B3 FCB 23 ; TABLE SCALAR
;
LC5B4 FCB 8 ; 8 + 1 LINE TABLE
;
; g/Sec BIN VDC #/HR
;----------------------------------
LC5B5 FCB 93 ; 8.4 0 0.00 0
LC5B6 FCB 36 ; 3.2 64 0.18 25
LC5B7 FCB 50 ; 4.5 128 0.37 35
LC5B8 FCB 69 ; 6.2 192 0.55 48
LC5B9 FCB 93 ; 8.4 256 0.73 65
LC5BA FCB 121 ; 10.9 320 0.91 84
LC5BB FCB 155 ; 14.0 384 1.10 108
LC5BC FCB 197 ; 17.7 448 1.28 137
LC5BD FCB 248 ; 22.3 511 1.46 172
;----------------------------------------------
;----------------------------------------------
; MASS AIR FLOW TABLE #2
;
; ARG = GMS/SEC + (256/SCALAR)
;
;----------------------------------------------
LC5BE FCB 48 ; TABLE SCALAR
;
LC5BF: FCB 8 ; 8 + 1 LINE TABLE
;
; gms/SeC BIN VDC #/HR
;----------------------------------
LC5C0 FCB 119 ; 22.3 512 1.46 172
LC5C1 FCB 133 ; 25.0 544 1.55 193
LC5C2 FCB 147 ; 27.6 576 1.65 213
LC5C3 FCB 163 ; 30.6 608 1.74 236
LC5C4 FCB 180 ; 34.1 640 1.83 264
LC5C5 FCB 198 ; 37.1 672 1.92 287
LC5C6 FCB 217 ; 40.7 704 2.01 314
LC5C7 FCB 237 ; 44.5 736 2.10 343
LC5C8 FCB 254 ; 47.7 768 2.19 368
;----------------------------------------------
;----------------------------------------------
; MASS AIR FLOW TABLE #3
;
; ARG = GMS/SEC + (256/SCALAR)
;----------------------------------------------
LC5C9 FCB 83 ; TABLE SCALAR
;
LC5CA FCB 8 ; 8 + 1 LINE TABLE
;
; gms/SeC BIN VDC #/HR
;----------------------------------
LC5CB FCB 147 ; 47.7 768 2.19 368
LC5CC FCB 158 ; 51.2 800 2.29 395
LC5CD FCB 170 ; 55.1 832 2.38 425
LC5CE FCB 182 ; 59.0 864 2.47 455
LC5CF FCB 195 ; 63.2 896 2.56 488
LC5D0 FCB 209 ; 67.8 928 2.65 523
LC5D1 FCB 223 ; 72.3 960 2.74 558
LC5D2 FCB 238 ; 77.2 992 2.83 596
LC5D3 FCB 253 ; 82.0 1024 2.93 633
;----------------------------------------------
;----------------------------------------------
; MASS AIR FLOW TABLE #4
;
; ARG = GMS/SEC + (256/SCALAR)
;----------------------------------------------
LC5D4 FCB 135 ; TABLE SCALAR
;
LC5D5: FCB 8 ; 8 + 1 LINE TABLE
;
; gms/sec BIN VDC #/HR
;----------------------------------
LC5D6 FCB 156 ; 82.3 1024 2.93 635
LC5D7 FCB 166 ; 87.5 1056 3.02 676
LC5D8 FCB 176 ; 92.8 1088 3.11 716
LC5D9 FCB 187 ; 98.6 1120 3.20 761
LC5DA FCB 198 ; 104.4 1152 3.29 806
LC5DB FCB 210 ; 110.7 1184 3.38 855
LC5DC FCB 222 ; 117.1 1216 3.47 903
LC5DD FCB 237 ; 125.0 1248 3.57 965
LC5DE FCB 255 ; 134.5 1280 3.66 1038
;----------------------------------------------
;----------------------------------------------
; MASS AIR FLOW TABLE #5
;
; ARG = GMS/SEC + (256/SCALAR)
;----------------------------------------------
LC5DF: FCB 207 ; TABLE SCALAR
;
LC5E0: FCB 8 ; 8 + 1 LINE TABLE
;
; gms/sec BIN VDC #/HR
;----------------------------------
LC5E1 FCB 166 ; 134.2 1280 3.66 1036
LC5E2 FCB 176 ; 142.3 1312 3.75 1098
LC5E3 FCB 186 ; 150.4 1344 3.84 1161
LC5E4 FCB 196 ; 158.5 1376 3.93 1223
LC5E5 FCB 207 ; 167.4 1408 4.02 1292
LC5E6 FCB 219 ; 177.1 1440 4.11 1367
LC5E7 FCB 230 ; 186.0 1472 4.21 1435
LC5E8 FCB 242 ; 195.7 1504 4.30 1510
LC5E9 FCB 255 ; 206.2 1536 4.39 1591
;----------------------------------------------
;----------------------------------------------
; MASS AIR FLOW TABLE #6
;
; ARG = GMS/SEC + (256/SCALAR)
;
;----------------------------------------------
FCB 255 ; TABLE SCALAR
;
LC5EB: FCB 16 ; 16 = 1 LINES IN TABLE
;
; gms/SeC BIN VDC #/HR
;----------------------------------
LC5EC FCB 207 ; 206.2 1536 4.39 1591
LC5ED FCB 213 ; 212.2 1552 4.43 1637
LC5EE FCB 219 ; 218.1 1568 4.48 1684
LC5EF FCB 226 ; 225.1 1584 4.53 1737
LC5F0 FCB 233 ; 232.1 1600 4.57 1791
LC5F1 FCB 240 ; 239.1 1616 4.62 1845
LC5F2 FCB 248 ; 247.0 1632 4.66 1906
LC5F3 FCB 255 ; 254.0 1648 4.71 1960
LC5F4 FCB 255 ; 254.0 1664 4.75 1960
LC5F5 FCB 255 ; 254.0 1680 4.80 1960
LC5F6 FCB 255 ; 254.0 1696 4.85 1960
LC5F7 FCB 255 ; 254.0 1712 4.89 1960
LC5F8 FCB 255 ; 254.0 1728 4.94 1960
LC5F9 FCB 255 ; 254.0 1744 4.98 1960
LC5FA FCB 255 ; 254.0 1760 5.03 1960
LC5FB FCB 255 ; 254.0 1776 5.07 1960
LC5FC FCB 255 ; 254.0 1792 5.12 1960 
If you cannot datalog, you can test the ACTUAL output of the MAF (not what the ECM thinks it is doing) with a voltmeter.
Back-probe the dark green and black wires at the MAF connector, start thr engine, and read the voltage at idle.
Datalogging is all good and great, but it doesn't differentiate between a failing MAF and failing connection between the MAF and ECM.
Back-probe the dark green and black wires at the MAF connector, start thr engine, and read the voltage at idle.
Datalogging is all good and great, but it doesn't differentiate between a failing MAF and failing connection between the MAF and ECM.
Supreme Member
Disconnect the electrical connector on the underside of the MAF. Should run fairly well, although a bit rich...if your problem appears to go away, look at the MAF, MAF relays, poor connections, etc. If it runs the same/has the same issue, MAF (and circuitry/components) probably isn't at fault.
Also, MAF cars are a bear to start and run properly with any leaks between it and the TB, like a cracked MAF hose, poor seal, etc.
Also, MAF cars are a bear to start and run properly with any leaks between it and the TB, like a cracked MAF hose, poor seal, etc.
Supreme Member
Quote:
Originally posted by Vader
Datalogging is all good and great, but it doesn't differnetiate between a failing MAF and failing connection between the MAF and ECM.
Thats why I was asking if he could datalog. If the computers A/D is seeing the MAFs output, then you definatly know that the system is reading in a signal. Alternativly, you can test the output right at the ECM connectors to make sure its getting a signal.Originally posted by Vader
Datalogging is all good and great, but it doesn't differnetiate between a failing MAF and failing connection between the MAF and ECM.
Member
The only thing I can say is from my own experience. This may or may not do you any good. I had a 350 ZZ1 motor installed with an accel computer. About... a few months after that, I was driving down the road and... the car shut off. Dead as a doornail. I came to find out the accel dfi computer was fried.
The... <insert terribly offensive word of choice here> shop I had the original and repair work done at claimed accel said I jump started the car backwards, fried the computer and wouldn't cover the replacement and made me pay 500 for a new computer. This being back in 1994. Anyway, that last bit won't help anyone, I just wanted to complain, lol.
You might wanna look at the computer, especially if you have any aftermarket computer eq attached to it or some such.
The... <insert terribly offensive word of choice here> shop I had the original and repair work done at claimed accel said I jump started the car backwards, fried the computer and wouldn't cover the replacement and made me pay 500 for a new computer. This being back in 1994. Anyway, that last bit won't help anyone, I just wanted to complain, lol.
You might wanna look at the computer, especially if you have any aftermarket computer eq attached to it or some such.
First of all I want to Thank You guys for the info it is well appreciated. I've been working on this for a few days and haven't been getting very far. And as for datalogging dimented24x7 as of the present time I can't but on monday I will be able to. I'm making up a patch cable to solder into the wiring under the dash so I can hook my laptop up to it and watch the computer. I have a 1995 Corvette that I run CAT software on and know how to write spread sheets and input it into my Prom ect.... I haven't gotten it done on this car yet because I thought I would have it running before now and didn't have the info to compare it to anyway. Thanks alot for the charts it gives me what I've been needing. My brother has my laptop borrowed and lives 50 miles from me and I'll get it back from him on monday. He has a 1994 Firebird and we have been both writing bin files and trading them back and forth for a couple of years now. Therefore I'm pretty comfortable with the fact that my ECM is good. It isn't acting bad and I can usually tell real quick or not if one is or not. Until monday I'll hook up the car the way Vader suggested and test it. I sure appreciate the pictures and everything you provided it take time and effort to do this and it is appreciated. I'll let you folks know how it tests out in the next day or so. I'm kinda thinking that the MAF is going to test out fine though, but want to be certain before I continue on to the next step. If I find the MAF to be good I'm going to pull the fuel rail and injectors and check them. I've already done all the voltage tests ect... and I have 13.67 volts at the injectors and 43lbs of fuel pressure and they have a good visual pulse when i hook up my Noid lights on them. I'll wait till after I run the laptop on it though so I can see the pulse in action. A little more accurate than looking at my Noid lights flash. Anyway "Thanks Again" for all the info folks. I've been working on cars for 25 to 30 years and really enjoy doing it as a hobby. I just became a member of thirdgen a couple of days ago and think this is a great site!!!! I never knew it even existed. A friend of mine told me about it and I've spent several hours so far this weekend just browsing around it and have even tried to help a few others out with what I know. It sure is neat to have found this site!!!! I see that there area several divisions around the country you guys ever get together for events and stuff????? Best Regards: cabsales1