When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
As the title states, I'm getting codes 33, 34, and 36. They popped up after I found a dirty looking ground on the firewall that I cleaned up while chasing an issue that led to the engine flat out cutting out stone dead at random and also where it would lose all ignition for fractions of a second once warmed up. After cleaning the ground, I took a long test drive and the codes popped up immediately but the original issue didn't present. When I was having the cutting out issues, there were no codes.
With the codes present, the car seems to run just fine. Maybe down on power a bit, but I'm not sure. It drives and idles normally. Unplugging the MAF makes no difference at all in how it runs or which codes show up. I did note that when I start the car, the wire doesn't glow like apparently it's supposed to for burn off. I did replace that relay 2000 miles ago, but when that failed, I don't remember it throwing all of these codes. I can't find any damaged or strained wires.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Originally Posted by Tuned Performance
Is the maf reporting gps to the ecm ?
Okay, what's gps and how do I check it? Side note, after a short drive today, on restart 40 minutes later, it bounced between 500 and 1500 rpm a bit until I put it in gear and it settled down back to normal. It started to rain, not sure if moisture affected something.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
The ecm sees grams per second, you can see ecm data with older otc pathfinder or snap on mt2500 or tunerpro rt using $6e adx file. Have you troubleshoot the code 33 or 34 with fsm ?
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Originally Posted by Tuned Performance
The ecm sees grams per second, you can see ecm data with older otc pathfinder or snap on mt2500 or tunerpro rt using $6e adx file. Have you troubleshoot the code 33 or 34 with fsm ?
The only tool I have to diagnose with is a paperclip. I work on my own cars out of a 1 bedroom apartment in the street, I don't have a garage or a lot of equipment. This is the only OBD I car I've ever had. Everything else is newer and much easier to diagnose since I can use a laptop and the appropriate software. Forgive me for not knowing all the acronyms, like FSM, I've had this car over a decade and this is the first non-mechanical issue it's had.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Thank you, I'll have to wait until it stops raining to be able to check this. Looks like I've already followed all of the diagnostic steps for 34 except for the last one, checking for 12V at the red wire on the MAF. My instinct from the moment I saw these codes is that the MAF failed, but I want to verify that before spending the $170 for a Delphi replacement. The Bosch doesn't seem to be available new anywhere. You mention using a program on my laptop to help aid diagnostics, but I don't have an OBD I connector for my laptop, only OBD II, so even if I downloaded that program, it still wouldn't be able to interface with my computer.
Thank you for the help, I'll report back whatever I find!
Waiting for the rain to stop so you can work on your ride is a fun time right? I'm still there as well. Keep at it, using the factory service manual and doing proper diagnostics is the way to success.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Yep, that's an expensive cable. The fun thing is if I buy it, I'll be able to diagnose the problem more easily, but then I won't have the money to buy the part to fix it. So please, I know using the factory service manual and using the proper diagnostic tools is the best way to go and suggesting it is like me asking which cam is the best to get more drivable power out of the 5.7 and you telling me I should just buy an LSX to put in.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Project cars are very expensive hobbies, and part of it is affording the tools that you need. Consider adopting a can-do mentality and find a way to get it done. Dropping $200 on a book and a cable is not the same thing as a $6k motor swap.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Originally Posted by Komet
Project cars are very expensive hobbies, and part of it is affording the tools that you need. Consider adopting a can-do mentality and find a way to get it done. Dropping $200 on a book and a cable is not the same thing as a $6k motor swap.
I've had this car for 14 years, it's not a project car or a hobby that I suddenly realized I got in over my head. It's my spare car, I've driven it across the country a couple times, Connecticut to California, and it's been modified some in that time. This is a continuation of the only problem that has stumped me for a long while, because it was intermittent for so long and it was a couple issues playing together. I'm now feeling like I'm toward the end of it, and I'd appreciate if there would be some understanding that money is tight and I need to fix this problem for as little investment as I can. A can-do attitude is what I have, what I don't have is a can-pay attitude. When I did have the money to get those things, I never had a problem that required them. Is anyone in the habit of buying things they don't need just because the possibility may exist that they need them at some point?
The motor swap comparison is just to highlight that $200 may as well be $6000 or $20000 for that matter, because I don't have it to spare just because it'll make my life easier.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
I followed the procedure below, and according to what's here, the proper diagnosis was a bad MAF. So I replaced it with a new Delphi unit and it's producing exactly the same codes as before, 33, 34, and 36. Even with the MAF unplugged, those are the same codes produced. I've searched and searched, and no one else has had this same problem that posted about it. Most people seem to have either 33 or 34, but not both. And the one guy I found that did have both also had a completely different running condition to go with it that was solved with a new MAF, if I recall.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Not to be an a**h***
Unless you are able to datastream what the ecm is doing and understand TPI systems, it's very hard for a remote stranger on the internet to help you.
If you changed the MAF and condition still exists, it ain't the MAF. Please check the entire MAF circuitry for integrity and functionality. All you need is a cheap ohm/voltmeter... and patience.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
I understand it's difficult without all of the diagnostic tools, but I didn't have the money to buy the tools and the MAF, so I kind of got stuck. I've checked the wiring for the MAF, burnoff relay, and MAF relay for shorts, bad grounds, and power, and all seem to be good on that front. I don't know if there's much else I can do without the proper diagnostic tools, so I'm not sure there's anything more to be done until life settles down enough to be able to get them. It generally runs fine with the codes but if it's been running recently, it sometimes won't idle on startup without holding the gas for a few seconds until it settles in. Which is a recent symptom. Starting to feel like the Chevy gods are just screwing with me.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Here's some more
Looks like Code 33/34 are generated by ECM when MAF readings are outside certain parameters. I don't know what they are exactly.
;--------------------------------------------------------
; ERR # 33/34 Params
; >> MAF Sensor Hi/Lo <<
;--------------------------------------------------------
LC21E FCB 167 ; If TPS > 65.2%, then use for MAF Default
; CALIB = Arg * 2.56
;
LC21F FCB 21 ; Gms/sec Scale factor
; gms/sec/IAC Count
; CALIB = Arg * 256
;
LC220 FDB 1024 ; 4 Gms/Sec default air flow offset
; CALIB = Arg * 256
For ECM to generate a code 36, ECM has to received a voltage between 0.4-1.90v upon engine shut off when burn off relay is activated. That's easy to check. Just probe B12 and record voltage immediately after shutting down engine.
;----------------------------------------------
; ERR # 36 Params
; >> MAF Burn off Diag <<
;----------------------------------------------
LC22C FCB 3 ; 0.3 Second Dly prior to Burn off
; CAL = Arg * 10
;
LC22D FCB 6 ; 6 fails req for ERR #36
; If HLM air meter
LC22E FCB 95 ; Fail B/O test if HLM A/D > 95 (1.90v)
;
LC22F FCB 20 ; Fail B/O test if A/D < 20 (0.400V)
Having said that, for the ECM to generate all these codes, I suspect the MAF is not producing any signal on B12. Why? You already swap the MAF and it's not the problem. So you should look to see if there is even power going to the MAF.
Good luck
Last edited by SbFormula; Dec 28, 2023 at 03:32 PM.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Originally Posted by Jack_88
I understand it's difficult without all of the diagnostic tools, but I didn't have the money to buy the tools and the MAF, so I kind of got stuck. I've checked the wiring for the MAF, burnoff relay, and MAF relay for shorts, bad grounds, and power, and all seem to be good on that front. I don't know if there's much else I can do without the proper diagnostic tools, so I'm not sure there's anything more to be done until life settles down enough to be able to get them. It generally runs fine with the codes but if it's been running recently, it sometimes won't idle on startup without holding the gas for a few seconds until it settles in. Which is a recent symptom. Starting to feel like the Chevy gods are just screwing with me.
Because the ecm is running on a default program in case of MAF malfunction or you are on limp home mode.
Last edited by SbFormula; Dec 28, 2023 at 02:43 PM.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Originally Posted by SbFormula
Having said that, for the ECM to generate all these codes, I suspect the MAF is not producing any signal on B12. Why? You already swap the MAF and it's not the problem. So you should look to see if there is even power going to the MAF.
Good luck
I appreciate the notes, some things I can check into. I do know the MAF is getting power when it's running, I checked B12 and it's getting about the same voltage the alternator outputs.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Originally Posted by Jack_88
I appreciate the notes, some things I can check into. I do know the MAF is getting power when it's running, I checked B12 and it's getting about the same voltage the alternator outputs.
That should not happen. Voltage on B12, when engine running, should be between 0.50 to 4.XX volts (warm idle to WOT)
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Originally Posted by SbFormula
That should not happen. Voltage on B12, when engine running, should be between 0.50 to 4.XX volts (warm idle to WOT)
I thought that was green that was supposed to be like that. From how I read the diagram, the voltage for red comes from the ECU at 12V, through the MAF power relay, and into the MAF. Where's the voltage stepping down? For the record, I've been measuring directly at the plug while everything is hooked up, I have a little wire that fits in there and comes out. I haven't been measuring anything at the ECM pinouts.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Originally Posted by Jack_88
I've checked the wiring for the MAF, burnoff relay, and MAF relay for shorts, bad grounds, and power, and all seem to be good on that front.
And how exactly did you do that? It takes time, method and patience. It means unplugging all relays, back probing ecm, etc..
Sorry to ask, but I've heard (we heard) many times "I've checked" & "all seem to be good"
You have to check what B12 is doing at the ECM connector using the original MAF (not Delphi). That will tell you if a signal is being sent.
KOEO you should get around: 2.5V
Engine running at warm idle: around 0.5-0.6V
Immediately after turning off engine, 0V followed by a brief reading that should be between 0.400-1.90V.
The codes are generated by the ECM upon what it is reading on B12. So that is where you need to look first and back track.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Originally Posted by SbFormula
And how exactly did you do that? It takes time, method and patience. It means unplugging all relays, back probing ecm, etc..
Sorry to ask, but I've heard (we heard) many times "I've checked" & "all seem to be good"
You have to check what B12 is doing at the ECM connector using the original MAF (not Delphi). That will tell you if a signal is being sent.
KOEO you should get around: 2.5V
Engine running at warm idle: around 0.5-0.6V
Immediately after turning off engine, 0V followed by a brief reading that should be between 0.400-1.90V.
The codes are generated by the ECM upon what it is reading on B12. So that is where you need to look first and back track.
I was measuring voltage and resistance values between the plugs at the relays, MAF, and ground. Any shorts or breaks in the wires would have shown themselves.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Originally Posted by SbFormula
B12 is Dark green!!! It's the MAF input.
I think I misread a reply somewhere and thought B12 referred to red. I've not checked anything at the ECM itself, I've checked every value from under the hood.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
I really appreciate your help, I'll check B12 at the ECU and see what sort of signal it's getting. I'll also check for continuity in the wires between B12 and the MAF, and for a potential short to ground.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Originally Posted by Jack_88
I think I misread a reply somewhere and thought B12 referred to red. I've not checked anything at the ECM itself, I've checked every value from under the hood.
You have to check what B12 is doing at the ECM connector using the original MAF (not Delphi). That will tell you if a signal is being sent. KOEO you should get around: 2.5V Engine running at warm idle: around 0.5-0.6V Immediately after turning off engine, 0V followed by a brief reading that should be between 0.400-1.90V.
B12 is the lifeline for the ECM. If the signal is non existent or outside certain parameters, codes are generated. You start there. Once you get some data, you'll have to back track, if necessary, to figure out why the signal is outside parameters.
I'm not saying I have all the answers. There could be some nasty gremlins. ECM can do bizarre things if grounds on engine, body and battery are not good.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
FYI and knowledge
When you unplug the MAF, the ecm relies on the IAC, RPM, TPS and tables to generate an estimated MAF reading. The signal on B12 becomes 0V, thus generating a code (most likely 34). On a scanner tool, it's hard to see because MAF voltage on B12 is not part of the data available through OBD1. The only clue you will get on scanner is, at idle, the MAF reading will be stable, holding the same value with constant RPM, instead of bouncing around a bit. The red line is MAF g/sec, the green line is MAF voltage. Notice how the red line is smooth when green line is at 0volt (MAF defective). Then, once MAF comes alive, the green line indicates voltage and the redline starts bouncing a bit.
I know... You are going to say "How am I suppose to know this?" TPI systems are complex and very sensitive. Throwing parts at them can be a nightmare approach.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
ummm...
Was just thinking
Did you clear your codes after installing the new MAF? Otherwise they might take a bit to clear themselves. IIRC, it's 50 cycles, depends on your tune.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Originally Posted by SbFormula
ummm...
Was just thinking
Did you clear your codes after installing the new MAF? Otherwise they might take a bit to clear themselves. IIRC, it's 50 cycles, depends on your tune.
So, yes, that was the issue after the new MAF. I reinstalled the original, checked the voltage for the MAF at the ECU, and it wasn't meeting the expected values. I installed the new one, and it was giving the expected values, and the codes cleared themselves by the time I finished checking all of the voltages. I've put about 150 miles on it since and had no codes, no misfires once warm, and it feels like it has all the power it ever did. So, until something comes up, I think that covers it.
To summarize what my issues were;
-Intermittent MAF codes
-Stumble when taking off immediately after startup
-Loss of ignition and stumbling when driven for a while, particularly under throttle
And each of these solutions were the things that made notable differences to the problems, but all problems weren't solved until all of these things were done;
-New ICM
-Cleaned bad ground on the firewall
-New MAF sensor
This was really annoying to diagnose because it was multiple faults in differing stages of failure and the issues were all intermittent. It wasn't until the MAF got much less intermittent recently and the help in this thread that it finally made sense. Thank you for all of the help, and I really hope this lets me use the car more regularly again without much issue. It still leaks oil, but it's not a big leak, so I'm not worried about it yet.
Re: Codes 33, 34, and 36 but it runs fine - '89 5.7
Originally Posted by Jack_88
Thank you for all of the help, and I really hope this lets me use the car more regularly again without much issue.
You're welcome!
If you still have the original Multec injectors, be ready for more problems ahead. Might be a good idea to change them. When they start to fail, you will get all kinds of "gremlins". Get yourself a back-up ECM while you can, because they fail too... intermittently What else? Fuel pump is a lot of fun to replace too!!!
BTW, did you use the Delphi MAF? What kind of voltage did you get at warm idle on B12?
