Gold86vette's problem is far different from Dennis's problem.

Gold86 seems to get the MAF and TPS signals OK at the CPU, yet there is a code 33. I would buzz out the burn-off circut to CPU wires - make sure they get to the CPU connector OK.

Dennis might want to try a new chip. Assuming the TPS is good. I have a good tested Thermomaster '85-'9? chip from HyperTech that he could try. Dennis is at the point where he can try anything except spending more money!!
Dennis - do you want to try my chip? I could give you a performance curve on your chip in my car, also - if you think it might help you fiqure out what is happening. I can also lend you a TPS - if you need to try one.

George

 

George,

I've replaced my tps, didnt need to, but frustration gets you to do about anything. Actually, I verified the tps is good with the autoxray and I made a wire harness to a multimeter to verify as well. I tried my stock prom and my TPIS prom with same the results.
Let me throw one more thing at you. When this problem first started my original maf malfunctioned. It is intermittent and sets code 33 and 34 with a few more I cant remember. Basically, I know that it is bad. However if I put it back on it will not set the code 33 like the new maf will. For example I know that I can make the code set (with 3 different maf, a new auto zone brand, a Bosch reman, and a new GM) by power braking the car to @1800rpm it will see 46 gms/sec and set the code. If I put my OLD maf and power brake @ 1800rpms it will only see @ 39-41gms/sec and will not set the code. My old maf calibrated a little different?


Dennis

 

Your original MAF was likelty a BOSCH unit, the otput is a variable frequency of 32 - 150Hz. If you could look at your MAF output with a scope, you could insure that it is a good clean signal. There could be noise from a pick-up or a ground loop problem. The noise could be getting counted along with the signal, making a bigger difference at lower frequencies, or low air flow. The answer could prove to be a mere matter of properly grounding everything.

I do not know the exact Hz to gms/sec, but I could find out. I imagine that suffient electrical noise to cause a problem would be easy to see on any old oscilloscope. A good test, if you can borrow the scope

George




[Modified by George West, 5:15 PM 11/11/2003]

 

Thanks Guys for the advice. I too believe I have an electrical problem which I think may have started when my fuel was contaminated (some poured something in my gas, about 3 gallons of milky white substance when the new motor had 200 miles on it - now it has about 240). The contamination caused my fuel pump to seize and blow my Fuel Pump fuse. After cleaning and further inspection I have noticed that some of the wires are now bare at the Fuel Pump Relay. After taping and cleaning up the wires near that It seemed to start and run again. Service engine soon or check engine light is always on. Damn you would think I would remember what the light says -its always on. Anyways with barely 200+ miles on it you would think it would run like new. Well guess what today I went out and started it and the code wasn't lit. Something worse it started exploding or popping out the exhaust - about 1 - 2 pops or bangs every 2-3 seconds. God why does this crap always happen to me when I need it the least. Now I need to check the cap, rotor, wires, plugs, fuel system, injectors, etc etc. I can't even handle the first problem. What could be worse than not driving your vet for 1.5 years while it is undergoing major engine / tranny work only to be plagued with problems. I have had this car for 11 years without any major problems or ever getting stranded until now. Now with the new engine / tranny / dana 44 the total investment in the last 2 years is 13,000. Thats 3,000 more than I paid for it in 92'. Needless to say I don't want to retire it for the year hurt so I need some advice. Should I just say screw it and wait till spring and attack the entire electrical system unlooming everything / checking and repairing, should I just go out and buy a new wiring harness, or just put a bullet into the ECM and buy a DFI? This intermittent stuff is killing me. The fact that my auto Xray only communicates with the car only when told the car is an 85 is killing me. The 1.25 second updates are killing me. The lack of overall data is killing me. Not knowing what the right bank O2 level is killing me. Aren't 86 computers supposed to be faster than 1.25 seconds. I have a device I got online from the Polish F body club but it doesn't communicate with my ECM. Could it be my ECM is bad or screwy? Why would it read as a 85 but not newer. I have also tryed 2 other 165's with no differences. One was a 87 f body and the other an 88 vette. Both communicate only with the Xray when set to 1985. Arrrrrrrgggggggghhhhhhhhh!
I am rambling on sorry guys had to vent on someone. I just want to run good and daily drive my 11 second vette is that too much to ask?

PS I want to get some pictures of the wierd wiring and post them here for you to see.

 

If you have a modified engine.....you have to increase the limits for code33 in the program on your prom.....
I've helped more than a few folk tune for more CI/larger cam/TB; and the only solution is increasing the limits.....
As above-if it sets it immed. at idle-then it's a different problem. Check for shorts/opens relays etc.
If you're borderline-you can try-set TB blade for IAC counts of 20 or so at idle/warm-then reset tps volt. to spec. That's about it!

 

Why would an engine with a small (10%) increase in displacement be able to pull more air through a cracked throttle (25%)? Vacuum is on one side of the throttle valve, and atmosphere is on the other - regardless of displacement. Now at full throttle (no throttle plate restriction), the big motor pulls more. But often a big motor with a big cam pulls less at low RPMs, since the cam usually favors high RPM air movement.

It is a possibility that can easily be checked, however. Just measure the vacuum at both sides of the throttle valve at the 25% point (where the code sets). If there is a larger than normal pressure difference, then Drive it's advice is right on. I can easily measure my pressures, if a comparison is needed. My 85 is very fast (12.9 sec), with all stock electronics.

I am guessing that the air movement sensed by all three of the MAF sensors that Chasenme has tried is on the high side. That strongly suggests noise on the lines. It could be from solid copper wires with no resistors, or from improper grounds, or from a floating shield.

I did have a code problem that went away when I switched to spiral wound wires, and added ground straps from the distributor, motor, chasis, and battery. But it was not code 33.

But that is just my not-so-humble opinion.

George

PS - If the frequency of the MAF is only a little high, and only at low RPMs, perhaps the best advice is Driveit's:

"If you're borderline-you can try-set TB blade for IAC counts of 20 or so at idle/warm-then reset tps volt. to spec. That's about it!"



[Modified by George West, 8:56 AM 11/12/2003]

 

George,

Believe me no one wants to find out more than I do what is EXACTLY wrong with this thing.
As for my plug wires they are the spiral core Accel 300+. Noise?
When checking the wire harness I used a cooling fan connected to the maf ground. Then powered the fan through the (power, burnoff ,reference and signal wires). Figuring that they could check good continuity with a mutimeter but not be able to pull any current. I can't find a wiring problem.
I've tried different throttle angles with varing tps base voltage and haven't found anything.However, I havn't tried to set IAC counts to 20 and reset tps. What will this accomplish? Throttle Closed or Open more at idle?

 

Code 33 gone. TPiS burnt me a new chip raising the stock (45gms/sec) threshold on the diagnostic code 33. Car runs great no codes!

Dennis

 

Dennis,
Congradulations! Let's look at the numbers:

At STP, 1 cfm = 34.636 gm/min or .577266 gms/sec
so the stock code 33 limit is 45 gms/sec = 77 CFM

At 1800 RPM the most air your 383 stroker could use would be
VE * 383 * 1800/3456 = 199 * VE

The VE (volumetric effeciency) can be as high as .8, if the throttle is wide open and there is a load on the engine. With the throttle partially closed, let's say that the VE might be as high as .4 when the motor is loaded - such as when you are power braking the car - usually it would be much lower. Remember that the code 33 only alarms if the throttle is at 25% or lower.

SO.... .4*199 = 79.6 CFM. So 79 or 80 CFM at 1800 RPM is a reasonable condition. The code 33 alarm was set for 77 CFM. poopie! Maybe it alarms with code 33 because it is suppose to!

If we try the calculatioins with a stock 350 instead (same VE), we get:
.4 * 350 * 1800/34565 = 72.91 CFM, with the alarm set for 77CFM.

If the stock alarm is set a little tight (which it is, assuming .4 VE), you have done the right thing. One MAF working and another not also starts to seem reasonable - even a +/- 5% calibration difference between units would make one work, and another not.

How much did you change the alarm limit? It looks like 80 is minimum, 88 would be 10% high. 88 CFM = 50.8 gms/sec

This has been quite an education for me. It looks like you can be comfortable with the action you took, but what a lot of work it was for you to get there!

George

PS - the wires you mention are quite good. Only the very low resistance solid copper wires must be avoided. And they can be OK if resistors are added.