Maf Code 33 and tps issues
04-05-2017, 07:06 PM
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Maf Code 33 and tps issues
I've had this car (87 Irocz) for over a year now but am only just now beginning to troubleshoot the code 33. the engine is a mystery, although the man I bought it from claimed it's a 350 bored .060 over.
Today I hooked it up to my laptop and took it for a drive, and immediately noted that at 2000 rpm the Maf is reading anywhere from 50 to 80 Grams per second, clearly a problem. It's worth noting that despite being set to .570v, not one of the THREE tps's I've put in will read above 87.5% when the pedal is on the floor.
The only thing here that's throwing me for a loop is that when the engine is off but the key is on, my winaldl shows a maf reading of 15Grams, and when I push the pedal to wot it goes up to 30grams.
So my 2 questions are these.
1:why would my maf be showing airflow where there is none?
2:why is the throttle affecting my maf readings?
Any help is greatly appreciated, and I intend to see this through till it's fixed so the next guy that has these issues can solve them.
I've noticed that the colder it is outside the more likely it is to throw the code 33, on a hot summer day I can be driving along fine, but if I hit a patch of cool air it'll hesitate and start missing. I've been driving above 2000Rpm to negate the code 33 but I'm worried it's going to run too rich for too long.
Update: so I've run the numbers, and I believe I had found the problem. It looks like the voltage I'm missing from my tps signal wire is crossing over into my maf signal wire. I'm going to confirm this by running a new temporary wire from the tps to the ecm and see if that changes anything. Even if this does fix it im still gonna have to dig into the harness and fix the crossover. More updates to come.
FINAL UPDATE, CODE 33 SOLVED: After banging my head up against a wall for 2 years, and dumping too much money into this project, I finally resolved the issue by doing a simple throttle blade adjustment. A combination of the throttle blades not being able to close fully and the tps being set to that as a base was the issue. I feel like an idiot for not doing this sooner. Thinking through the issue after fixing it, this was clearly the first thing I should have tried.
Today I hooked it up to my laptop and took it for a drive, and immediately noted that at 2000 rpm the Maf is reading anywhere from 50 to 80 Grams per second, clearly a problem. It's worth noting that despite being set to .570v, not one of the THREE tps's I've put in will read above 87.5% when the pedal is on the floor.
The only thing here that's throwing me for a loop is that when the engine is off but the key is on, my winaldl shows a maf reading of 15Grams, and when I push the pedal to wot it goes up to 30grams.
So my 2 questions are these.
1:why would my maf be showing airflow where there is none?
2:why is the throttle affecting my maf readings?
Any help is greatly appreciated, and I intend to see this through till it's fixed so the next guy that has these issues can solve them.
I've noticed that the colder it is outside the more likely it is to throw the code 33, on a hot summer day I can be driving along fine, but if I hit a patch of cool air it'll hesitate and start missing. I've been driving above 2000Rpm to negate the code 33 but I'm worried it's going to run too rich for too long.
Update: so I've run the numbers, and I believe I had found the problem. It looks like the voltage I'm missing from my tps signal wire is crossing over into my maf signal wire. I'm going to confirm this by running a new temporary wire from the tps to the ecm and see if that changes anything. Even if this does fix it im still gonna have to dig into the harness and fix the crossover. More updates to come.
FINAL UPDATE, CODE 33 SOLVED: After banging my head up against a wall for 2 years, and dumping too much money into this project, I finally resolved the issue by doing a simple throttle blade adjustment. A combination of the throttle blades not being able to close fully and the tps being set to that as a base was the issue. I feel like an idiot for not doing this sooner. Thinking through the issue after fixing it, this was clearly the first thing I should have tried.
Last edited by Suekam; 09-10-2017 at 03:14 PM. Reason: Adding Info/issue resolved
04-07-2017, 02:13 PM
#2
Re: Maf Code 33 and tps issues
The maf will show air flow when disconnected. I'm not positive but I think lv8 is in play in conjunction with the tps. Code 33 throws when 45 gps is seen when the engine is first started or less than 1/4 throttle rpm less than 2k rpm. Idle should be about 8 gps .73 volts .
I think the maf receives a 5v ref the voltage get higher with gps flow maxing out at 255 gps.
Sounds like you might have a bad Ecm.
Have you checked the 5v ref grey wire to the tps ?
I think the maf receives a 5v ref the voltage get higher with gps flow maxing out at 255 gps.
Sounds like you might have a bad Ecm.
Have you checked the 5v ref grey wire to the tps ?
Last edited by Tuned Performance; 04-07-2017 at 02:35 PM. Reason: ??
04-12-2017, 12:12 PM
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Re: Maf Code 33 and tps issues
The maf will show air flow when disconnected. I'm not positive but I think lv8 is in play in conjunction with the tps. Code 33 throws when 45 gps is seen when the engine is first started or less than 1/4 throttle rpm less than 2k rpm. Idle should be about 8 gps .73 volts .
I think the maf receives a 5v ref the voltage get higher with gps flow maxing out at 255 gps.
Sounds like you might have a bad Ecm.
Have you checked the 5v ref grey wire to the tps ?
I think the maf receives a 5v ref the voltage get higher with gps flow maxing out at 255 gps.
Sounds like you might have a bad Ecm.
Have you checked the 5v ref grey wire to the tps ?
I will check the reference wire when I get home but last week I did confirm that both the maf and the tps are being supplied with 5 volts. A few months ago I replaced the ecm and the prom with a new ecm from Napa and a street chip from hypertech, the original prom in the car was for a 305. 6months ago I replaced the maf, and last week I replaced the tps. More info to come, I've been seeing up to 80 grams a second under 2k rpm while datalogging.
04-17-2017, 07:44 PM
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Re: Maf Code 33 and tps issues
Issue not resolved yet, but further datalogging has shown the problem to be intermittent, I'm beginning to suspect an ecm grounding issue, possibly a charging system issue. when it trips the codes the dash voltage guage drops from 13~14 to 11~12, which may be a side effect of the limp home mode the ecm enters when the 33 is tripped.
I purchased a new maf relay and made extra sure I plugged it into the right harness, and my idle air is down to just over 8 grams/s which I believe to be the high end of normal. there's lots of electrical tape and crimp connectors in my wiring harness, I'm beginning to think the previous owner was drunk when he worked on this car.
All that aside, I'm in the process of trying to find another daily driver so I can park this thing for a full workover. I'll try my best to resolve my issue and post the results here. My first advice would be if it's in your budget, get a datalogging setup and see what the ecm thinks is happening.
I purchased a new maf relay and made extra sure I plugged it into the right harness, and my idle air is down to just over 8 grams/s which I believe to be the high end of normal. there's lots of electrical tape and crimp connectors in my wiring harness, I'm beginning to think the previous owner was drunk when he worked on this car.
All that aside, I'm in the process of trying to find another daily driver so I can park this thing for a full workover. I'll try my best to resolve my issue and post the results here. My first advice would be if it's in your budget, get a datalogging setup and see what the ecm thinks is happening.