What are some signs that the Mass Air Sensor is bad? I think mine is bad, but would like to know what experiences some other people have had with them. I am relatively new to the TPI scene. It is on a 1985 IROC-Z 5.0L TPI. Thanks in advance.

 

if it is the maf only there will be a ses light, code 34 and code 36 for the burn off relay which sometimes a light will not come on for, depends on the cars mood i guess...my burn off circuit went and when i started my car, it fired right up, then immediately died with no light...after i couldnt figure out what the hell was going on, i took it somewhere where they said it was the maf, so it was replaced then the problem started all over again...turns out the burn off relay wasnt working which is why the maf was f'd up...the moral of the story is that a burn off circuit costs 20 bucks and the maf cost 200 so...

 

What is a burn-off circuit and where is it located?

 

I am going to try to describe what my car is doing. When I first start it up when it is cold, when I go to take off, it barely runs until I can get at least 1000 RPM out of it, then it is fine. When slowing down, it will idle down to 500 RPM or lower, barely running. Also, when I stand on it, it has a horrible surging above 3000 RPM or so, but it is not consistent. It doesn't seem to have any problems in the mid-range, but off-idle and wide open is where it is having problems. I know this isn't much to go on, but I would appreciate any input. Thanks in advance.

 

hm, sounds pretty crazy...the burn off circuit superheats the wire sensor in the maf after the car is off to burn off all the sht build up or whatever to clean it basically but by what u said, this cant be the problem...are u getting any ses light?...with all idle problems, clean the sht out of ur iac valve and check ur tps and clean the whole throttle body with carb cleaner...if ur not getting any codes, im not really sure what else to tell ya, someone should have more info

 

I think I need a new burnoff relay as well. I got code 36 but I also was told that my burnoff relay is bad. I'm getting low fuel pump voltage as well. Does anyone know what that problem might be?

 

I am not very enlightened when it comes to TPI's. What is the IAC valve, and how do you check the TPS? Will a burn-off relay fry a MAF unit?

 

the iac valve is under the throttle body on the left side, it controls the idle basically, take it out and clean it with carb cleaner...check in the tech boards, there is a article about it and also the tps which is a sensor also on the left side of the throttle body it needs to be set a certain voltage- check the tech article...the burn off relay can fry the maf...
also check out iroczone.com tech boards

 

Ok, here goes.

On the 1985 TPI systems there are NO burnoff or power relays. Both of those functions are handled by the MAS module, which is a very expensive little box that is piggybacked on the ECM.

With that said, your problem with the very low idle and off idle hesitation could very well be caused by the PROM chip. There was a service bullitin on the early TPI's for those problems along with a false code 34, torque converter lockup problems and others.

If the PROM chip was never replaced in your car you need to do that first and see if any of the problems remain.

 

see, someone knows what theyre talking about

 

At this point the car has a Hypertech Stage 1 chip in it. It has had this since I bought the car. If this gets too involved, I am just going to pull the setup that is in it now and drop in my carbureted 350 and eliminate all the FI crap. I would rather not until I have a chance to put another set of heads on my 350, but I don't think it would take many parts on this FI stuff to equal the cost of the heads I want to get.

 

Ditch the hypercrap. Last time I checked the Factory chip cost $44 from Chevrolet. By your idle it sounds like they copied the bad prom info from the first GM chips.

Also, you may want to look into getting your injectors cleaned and flowed.

A bad MAF will usually set a code and turn on the ck eng light, but don't count on it. Other symptoms are; spitting black smoke, stalling as soon as you take your foot off the gas, stalling while idling for long times (stop lights etc)

 

What would be recommended to use to clean the injectors?

 

It will entale either removing them and sending them off to Crusin Performance, or another place that does that work or making your own injector cleaning rig. Do a search for it, someone here made a simple, easy to use injector cleaner. But doing it yourself you won't be able to flow check the injectors to be sure they are performing like they are supposed to.

 

After driving the car to lunch, when it is cold, it acts like it has a carburetor on it. When you try to step on it too much, it bogs out temporarily and then takes off, and when you WOT, it really bogs bad. It gets tremendously better as it warms up. The idle problem goes away, but it still lacks some on top end, you can feel it surging a hair. It acts like it is lean. This all just started a few weeks ago. Would putting K&N stock replacement filters on it cause this?

 

Not in the least.
If you truly think your MAF is bad, unplug it and try to start the car, I'd bet it won't start and if it does it won't stay running very long.
The problem you describe with acceleration when the engine is cold is exactly what one of the symptoms of the bad GM chip was, "cold drive away problems" were the words they used, it would surge and chuggle and lunge when trying to accelerate when cold.

 

But what about the top end? Could it be related? Also, I'd hate to have to put a stock chip back in. I think the car runs pretty well for a 305 car. A friend of mine had an 86 TPI Z28 and my car is over a second quicker than that one. Mine seems to run good. I'd hate to lose that.

 

The hypercrap only makes adjustments to WOT fuel and spark.

The reason your car is a second quicker is that it had a 215hp engine and in 86 it was 190 hp, also the state of tune of your engine and his probably played a part not to mention rear gears.

 

Where would be the best place to try to find a stock chip? It would be worth a try to fix my car.

 

^^^^^

 

If you need the part # for the chip to order one I still have mine.

 

What is it?

 

HLM 3800, Prom chip for 870 ECM

 

Last night I was sitting in my car, the idle was alright, but when I went WOT in neutral, it revved up to about 3000 RPM and then started surging really bad, like I was hitting a rev-limiter. When I let off a little bit to probably 3/4 throttle or so, it revved on up without any problems. Any ideas? Thanks in advance.

 

you need to hook a scanner to it, it sounds like under or over fueling is happening.

 

Poor driveablity will consume dollars like you wouldn't believe. Before you start changing the expensive stuff like the computer, do the cheap stuff and go easy on your wallet.

If you have the trouble codes, that's a start. But what you need is to methodically check everything that affects the spark, fuel and air to make sure they are working properly.

Plugs, wires, secondary ... when's the last time you had the cap off? Mine looked like something from the Titanic, even though you can eat off any other surface in the car.

An MAF that doesn't work ... doesn't work. You won't be able to even light the engine, or it will only start in a limp-home mode. Unless it is throwing a specific SES code, I don't think that's the place to start looking.

IMHO, you want to check the following:

Make sure that fuel pressure is consistent, and within spec. Low fuel pressure will cause most, if not all, of the surging and hesitation. If you ever ran it dry, it's about ten times more suspect to fail, and if it's almost 20 years old, you got your money's worth. Might be time for a new one. And look at the filters, too, might have got a bad load of gas somewhere.

Giant caution flag: the fuel tank is almost impossible to access, and anytime you ever use gas, you have to treat it just like the explosive it is.

Injectors need periodic maintainence, regardless. Most service stations and oil change places will have a "hang-on" pressurized system that bypasses the engine fuel system and runs off a strong, concentrated solvent. The early GM injectors are highly susceptible to fouling and again, given the age of your car, this is something easily fixed.

The throttle body can coke up massively. My 39,000 mile Formula has had its TB removed and cleaned three times, and will get it a fourth before spring. The dimwit GM design that put the port near the throttle blades practically guarantees sticking. Remove it, clean it FRONT AND BACK in brake solvent, blow out the passages, then reinstall with a new gasket.

Then you can reset the Throttle Position Sensor and the Idle Air Control. You adjust TPS with a multi-meter, pretty straightforward if its working right, there's a tutorial on the board. The IAC is simply a reset, no adjusting to speak of. Get the service manual for your car, it's pretty easy, too. My GM manual says don't ever get solvent on it; if it's that nasty, it needs replacing.

There could be some other things going haywire, such as an EGR valve hanging open, a bad O2 sensor or even a CLKC knock sensor can even cause problems.

See if your library has the shop manual for your year and engine.

There is a clear, simple trouble shooting decision tree for driveability with tests to perform and suggested actions. Give it a try, and you should get to the right answer, eventually.

 

Thanks for the tips. I do appreciate them. I picked up a used MAF sensor over the weekend and changed it and my car is back to normal. I have heard from many the if the MAF was bad that the car would not run at all. I am not sure what wass wrong with mine. I do need to do a thorough tuneup on the car, but in the middle of winter is not a good time. We'll see though. I have not run the car close to dry on fuel. I don't let it get much under 1/2 tank of gas, but that doesn't mean a previous owner didn't do it.

 

Im really confused on this right now, you all say the car will not start without the MAF? that is wrong, because, my car, the MAF is unplugged, because it is no good, and i have to buy another, my car bogs when i have it plugged in, but when i have it unplugged, it runs ok, it still bogs, but however, my car will start, never have problems starting it either, im confused?

 

No, the car should start with a bad MAF or disconnected one. It will run i either "limp home" mode or on a preset air/fuel raito table (not optimal).

 

Would a bad MAF cause my car to stall or should I say miss at 3500 rpm?

 

A bad MAF can cause all sorts of problems at every RPM setting depending on what exactly is wrong with it.
If you have a "miss" at just one RPM level don't go replacing a $500 MAF to try and fix it. It is highly doubtful that a bad MAF would cause a problem at just one particular RPM.
You need to hook up a scanner and see just what is going on when you see the problem.

 

is it a bad thing running without a MAF sensor???

 

In a word, yes. Gas mileage will go in the crapper for one

 

yikes, yes, gas is bad for me since i dont have it, well i have it, but the lil wires inside it are gone, anyways to fix it? and what can happen runnin with it like that? every seldom my car will die when i stop

 

my car will start then run for a few seconds then slowly start dropping rpm and die help its putting out a code 42