Hi Everyone,

Corvette C4, 88, L98. When warms up - almost every time during the regular driving car spontaneously (single time) starts shaking under load and immediately gives 33 code (SES), which means High MAP. I made a diagnostic based on googling, service book and forums - cleaned all contacts, replaced both relays (burn-in and power), cleaned MAP, replaced IAC and set TPC at 0.55 - same result. Restarting the engine removes SES light, but then it appears again after a couple mins of driving. I connected ADLD cable from RedDevil and used ALDLroid app to log the car behavior - and MAP signal looks very strange for me - most time it shows 0, and appears only when I'm pressing throttle. The signal usually not high (0.5-0.8 V), however, after a while - it becomes way higher (4-5V) during the same style of driving. Seems like this is exactly appears when I receive code 33. O2 sensor diagrams looks good to me - at the beginning it smoothly goes high and then becomes erratic. Do you know where should I take a look? (diagrams are attached)

 

MAF sensor itself most likely.

 

Forgot to add - the car is always in Open loop

 

Which Data stream file (ADX file) are you using with ALDLdroid? 88 is a MAF car. There is no map sensor unless somebody has converted the car to speed density.

Try A028 or A059. Note: the 86-88 and 89 datastreams are very close with only a few bytes that differ between them. I use my own adx files with ALDLdroid, but I will take a look at the provided ALDLdroid adx files.

More info: https://www.corvetteforum.com/forums...post1606633915

 

Then I'd look at the O2 sensor as well, but MAF first.

 

@tequilaboy , this is a valid point. Originally I used the one, which was detected (?) by ALDLroid as a default one, but seems it is not correct.
So I just made additional logging by using 2 different .adx and 2 different applications - ALDLroid (.adx name - A028-L98-LB9-1985-1988-9600.adx ) and TunerPro RT (1985 5.0 (LB9) TBI F Body & 5.7 (L98) TPI Y Body 1226870 $1F.adx). The results a bit different now and MAF seems more stable, but the issue with SES (code 33) still exists (same behavior). For some reasons none of .adx files logs Code 33, but it can be read with paper clip method. During both tests I found strange behavior of IAC sensor - in the middle of the diagram - it falls to almost <20 steps for a second. But I replaced it about a month ago. Open loop during all 15 mins driving though.


TunerPRO with IAC falling

ALDLroid with 028 adx

 

@vader86 The O2 seems to be OK too - it rises slowly and then starts to be erratic

 

I took a look into the ALDLdroid adx files with TunerPro. The A028 file is only 160 baud.

If you're going to use the ALDLdroid provided adx files, I would suggest that you use A059 (A059-L98-LB9-1989-9600.adx) for 8192 baud scanning, but make note of the $32B/$6E datastream differences that I posted in the link above (irrelevant with one exception since this adx doesn't decode every single bit and byte included in the 63 byte datastream: the Burnoff Failure Check Complete flag is not used in $32B).

Monitor the MAF signal with respect to the throttle position. Also compare the MAF signal to the unlimited airflow signal (which is labelled as the MAF Raw Input in the adx file).

Side note: Code 33 should only be set under relatively light load conditions. It should be only set below 14.8% tps (approx. 1.10 tps volts). It is a plausibility check of the maf sensor signal with respect to the throttle position. Likely cause is an open circuit on the maf signal wire.

;--------------------------------------------------------
; ERR 33 Params, TYPE 32 ECM
; >> MAF Sensor Hi <<
;--------------------------------------------------------
LC210: FCB 38 ; If TPS >= 14.8%, disable ERR #33
LC211: FCB 45 ; If Air Flow GT 45 gm/sec, SET ERR #33
LC212: FCB 96 ; If > 600 msec, Set code ERR 33, (Num + Arg * 160)
LC213: FCB 8 ; 800 msec, ERR #33 Min time req. (Num = Arg * 10)
LC214: FCB 128 ; If RPM > Disable ERR 33, (TBL1, NTRPM) 2200 RPM
LC215: FCB 100 ; If Pump Volts <= 10 vdc, Bypass ERR 33
;--------------------------------------------------------

 

Coolant temp ... F ? or C ? Temp is very low if reading fahrenheit .

 

@tequilaboy , I tried 028 file and 059 - and only 028 worked. With 059 I got error - "No response from ECU". Seems like for some reasons I can't connect via 8192 baud (I guess??). But 028 is not capturing error codes at all, which are exist (per paper clip check). Do you know how to enable 8192? (using reddevilriver 12 pin cable).

@C409 - Yeah, thats a good point! The difference between Gauge and ECU is about 50 degrees - when I had 150F in the dash, scan showed 100-110F. Ordered cooler sensor to check if this is an issue.

 

Enable debug logging and check the debug log text file. Typical path on android device: ...\Android\data\com.sgiroux.aldldroid\f iles\debug\debugLog

It may take some time to connect and may work better trying to connect with the engine running.

 

What is the minimum temp for closed loop ?

 

Min Temp for closed loop: 40.25 °C (104.45 °F). Coolant temperature must be greater than the minimum rather than greater than or equal to the minimum, so really 41 °C (105.8 °F).