Just got my L98 engine redone for my 1988 and need some help.
It's about 450hp(300 at rear and over 500ft/lbs of torque with long tube headers, resonators, borlas and 28lb injectors)

Symptoms:

Stock chip keeps thowing Mass Air code.
Put in a chip from a 6 speed and Mass Air problem gone but car runs terribly - loss of power, running rich, hard starting, stalling, and fuel is about $30 a day for a 20km trip!

Ordered a custom chip and car ran great but on the highway Mass Air problem returned.

Desperate and need help with a solution and/or the location for someone who can flash my chip a.s.a.p.

I'm in the Toronto area.

Thanks!

 

Which MAF codes did it throw?

 

I'm not sure about the L98's, but I know that if you push too much air through the LT1 Mass sensor it will pull a code 103 (that you have exceeded the limit of the mass sensor...)

You may want to see what code it is throwing and log it. As you probably know the symptoms of a bad mass sensor as it will cause the car to run erratic, if you suspect it is the Mass sensor, simply unplug it and see if it returns to running smooth... If you replace the mass sensor I'd replace the relay as well...

Hope this helps...

Mo

 

Code 33, Morley.

All sensors and relays were replaced when I dropped the new engine in, Mo.


Thanks for the thoughts; I appreciate it.

I will try the disconnect anyway but my tech guy thinks it's an eprom issue; I just might need someone who can burn chips near Toronto so they can have the car and do it right.


Any other ideas?

Really desperate.

Thanks again to both of you.

 

I got this from somewhere a while ago..don't remember where exactly. Its kinda long but has some good info in it.
The PROM shouldn't be the cause of the problem..but it may make it more pronounced.

There are three codes that pertain to the MAF sensor: Codes 33, 34, and 36. Code 33 (mass air signal voltage high) is set when the computer sees a high mass air reading at low engine speeds. In other words, there appears to be more airflow through the MAF sensor than the engine can physically breathe at a specific throttle and rpm.

Code 34 (mass air low) sets when the computer registers less than 5 grams of airflow at idle or 2.5 grams/second of air when the engine is first started. The mass air wire inside the MAF sensor should heat up after the car shuts off to clean any contaminants from the wire. When this fails to happen, the computer shows a Code 36 (mass air burn-off malfunction). We'll address and troubleshoot each code individually.


The mass air sensor is a simple design. It's comprised of a wire that heats up when the car is running. The air entering the engine through the MAF sensor cools the wire. The more air ingested by the engine, the more air must flow through the sensor. More air means a cooler wire. The computer knows how much air is entering the engine by the temperature of the wire inside the MAF sensor. The air/fuel mixture is dependent upon having accurate readings from the MAF sensor. If there were a problem, a Code 33 or 34 would be set. Once a Code 33 or 34 appears, the MAF sensor will shut down and the car will go into "basic strategy" mode, aka limp-home mode, until the key is turned off for at least 15 seconds. You'll know the MAF has stopped working when, in Chris' words, "You let off the throttle and it feels like an anchor just dropped."

A Code 33 can be set for several reasons. It appears if the dark green wire (circuit 998) has an open circuit or a bad sensor; if the black, burn-off control circuit wire (circuit 900) has power with the car running; or if the system has a bad ground. You must check for an open circuit on 998 at the ECM on connector B12. There are several places to check for a grounding problem. The cast-iron-headed '85s and '86s have the grounds on the rear of the driver-side head. You'll have to pull the wiper motor to check. The aluminum-headed '86s and '87s have a pack of grounds next to the oil-temp sensor and filter. On the '88 and '89 Corvettes, the ECM, dash, and sensor grounds are on a lower lefthand-side bellhousing stud.


A Code 34 could be set for several reasons as well. A bad ground, an opening in the ducting between the MAF and the throttle body, incorrect minimum idle-air setting of the throttle body, or a worn throttle body can all cause a Code 34. Typically, a worn throttle body or a bad ground will set a Code 34 intermittently (every third or fourth time). To see if the minimum idle air is causing the problem, open the throttle slightly as you try to start the car again. If it's easier to start, check the minimum idle air.

To check the throttle body, simply depress the cruise-control bellows and observe if the throttle-body linkage moves laterally instead of only rotating on the shaft. If there is noticeable movement, your throttle body is worn and the engine is getting unregistered air through the gaps.

'86-'89 Corvettes use a powered fuse link and connector that supplies power to the fuel pump and MAF relays behind the battery. The '85 Corvettes do not use relays for the MAF, but instead use a module next to the ECM. This module rarely goes bad; but to check the module on '85 Corvettes, look for 12 volts at connection E on the MAF with the engine running. Then, run the engine for at least 5 minutes, turn off the key, and check for 12 volts at connection D (MAF burn-off). The powered fuse link is a common cause of intermittent MAF codes. Check the connection and wire for a possible open circuit.
The oil-pressure switch is another possible cause of intermittent MAF codes. If the engine feels as if it has an intermittent hiccup with a fuel pump and MAF code set, the oil-pressure sensor would be the place to start. If the switch is bad, the engine tries to start because power to the pump at startup is fed through the ECM's fuel-pump-relay drive (connection A1).

The relays changed in late '87. Relay No. 14089936 operated the MAF power, burn-off, and fuel pump. Although not always accurate, the connectors for the 9936 relay are the gray connector for the burn-off circuit and the black connector for the MAF power circuit. You'll notice that the new connectors are weather pack connectors to seal out moisture.
To check that the MAF burn-off is getting power, look for 12 volts at the MAF connector position E.
If you get a Code 36, MAF burn-off malfunction, it should immediately reveal itself at startup and it won't affect performance. '85 Corvettes will never show a Code 36, only '86-'89 Corvettes. You can check to see if the ECM is calling for an MAF burn-off by running the car for at least 5 minutes, and checking the black wire at connection F (circuit 900) on the gray connector. It should be grounded for approximately 30 seconds. This is the ECM grounding the wire to actuate the relay. If there is no ground, the ECM is at fault. If you have ground, check the power to the relay. If the relay is sending power to the MAF, check that the dark blue wire (position D) on the MAF sensor connector has power.

Chris has spent some time adding wires, meters, test lights, and jumpers, chasing down several specific reasons why Codes 34 and 33 will appear. Here is what he found: The dark green wire from the ECM to the MAF (circuit 998) can short to ground or short together with circuit 450 (black or black/white) and cause a Code 34. To get a Code 33, circuits 998 or 450 could have an open circuit. Recently, Chris has seen a few cars for which the only cure was to run new wires for both circuits. This cured the intermittent codes immediately.
Checking The Minimum Idle Air: The first step in checking the minimum idle air is to put the car into Field Service Test Mode. Do this by putting a spade connector into the A and B positions of the ALDL connector. With the key on and the engine off, the fan will turn on and the SES light will flash. Also, the Idle Air Controller (IAC) will fully close.

 

Morley,

AWESOME! Just awesome!

I've suspected a bad ground - other issues with the car - but never thought about that regarding the mass air.

I'll pass it on to my tech guy and see what happens.

Maybe Friday the 13th will be lucky for me.

Thanks so much! I really appreciate it. Have a great weekend.

 

Morley,

Took your suggestions to my tech guy.
Grounds are fine.

Found a guy to flash eprom.

I hope that's it.

If you or anyone else has any other ideas, I'd really appreciate your thoughts.

 

Under ecm constants is maf high diagnostic (error 33) threshold.
I've found that on any engine with more than a few bolt on mods you need to increase this value from the stock 45gps to about 75 or even 125gps.

 

drive it,

Thanks for the very useful info. Gonna try again to see if wiring problem exists and, if not, will pass on those numbers to Eprom Flash Guy (sounds like a super hero - hope he is).

Take care and thanks again!


UPDATE:
No grounding problems; fuseable link okay, ran new wires on 998 and 450.

Tech guy is convinced that it is an eprom issue and that "drive it" is correct about raising value - to about 120.

Wednesday/Thursday I find out.


Thanks to all for your advice and help!

 

Wednesday/Thursday? Is that what I said last month?

Still no remedy for my MAF 33 problem so I just e-mailed pcmforless and hope they can help me like they've seemed to be helping others here.

Is that the way to go?


So, is it that hard to find a chip burner/tuner on the Toronto area?

Guy we found was totally unreliable. Another guy was clueless about TPI - no software, connector, clue.

I had to come back and give an update after all of the truly great help I have received.

 

I share your pain - similar problem (I am posted also in this section) - but different animal. Mine is an '85 L98, few mods, nothing Too radical, but it adds up to more MAF signal than the threshold for the code to set (code 33, MAF signal high). So far I've been able to work around it by setting the TPS signal higher - turn it up to about .62v at idle. This seems to push the combination of signal readings that the ECM uses to set the flag out of bounds - the combination of MAF reading above 90 (this is for the '85), TPS less than 1/2 throttle and RPM less than 2200 doesn't occur. So far. The real "cure" would be to edit the PROM and change the set point value for that flag. The probem is (for me - not for you) that the '85 chip and ECM does not have the flag settings for diagnostic codes on the PROM where they can be changed - they reside (as far as I can figure out) on the ROM chip - something that is NOT editable. Before I can change the flag setting for this code I'll have to do the upgrade to an '86 or newer ECM.... Deeper and Deeper!

 

Thanks man. Frustrating it is.

You did give some new info that I truly appreciate and never thought of.

Should I luck out and find someone to flash my chip, I'll definitely pass on your situation/solution as well as the others.

Vettes and women: so nice to look at and drive; but, hang around long enough and it's gonna lead to frustration and cost$$$ eventually, huh?


Thanks again!

By the by, ain't givin up my love for Vettes nor Women.

 

Okay. So, after reading all of the hype about PCMFORLESS, I've e-mailed them. They sound awesome and very willing to try to help.

Gonna try to e-mail my dyno results to them and see what happens.

[Please, please let this work - he says to himself ]

 

I hope that works for you. I took the drastic approach and converted to a 1227730 (MAP instead of MAF) because I understand the MAP tuning stuff better and got tired of code 33. Even though there are people running high HP with the MAF, it always seems that had to rig something and I dont believe that it isn't a restriction. I am not recommending it, but it is an option and the swap was pretty easy.

 

Wooooohooooooo!

Got my piggyback chip from pcmforless on Monday, put in in about 10 minutes, took the car for a boot, and man oh man does it rip!

Alvin, you rock! You are the man, indeed!

You have to be for solving so many of my vehicle issues virtually in the dark with just one of my dyno sheets and some e-mailed symptoms and specs.

No more mass air code and now I know what 400+ hp (300rwhp) and 510ft/lbs of torque feels like.

Still have some minor issues with high idle and open throttle in overdrive at high speeds but the car has been running so rich and the idle has been manually adjusted so many times that I think I need to give it a good work over (plugs, timing, idle adjust).

At any rate, I know where to get my Eprom adjusted if that turns out to be the cause.

Thanks to all for your input and, again, to Alvin - the case of beer awaits you should you find yourself in the Toronto area.

 

The high/surging idle and the overdrive situations have been resolved.

Thanks to tech tips, I readjusted the idle and TPS properly and idle is now proper - for my car anyway.

Much to my surprise, that readjustment solved a 10 year mystery for me regarding voltage drops under load with the ac/defrost on.


As for the overdrive issue, it turned out to be the kick down cable.


Thanks again to all!

 

Awesome thanks!!

 

Congrats on ironing out the problems! Alvin is professionalism at it's best!