Hey guys, I need some help bad. Last week my mass air went, guy before me removed the front screen and a leaf took the hot wire out. Got a new mass air and now I have another problem. the car idles at 1500 RPM and has a stumble when you hit the throttle. Now when I disconnect the mass air and run the car, it idles normal, but still has the stumble(obviously because the ecm has no reading how much air is going to the motor). What would cause this? The car is a 350 vortec heads, edlebrock lower and runners, mild cam(comp 08-501-8) .488/.495 210*/218* 24#/hr injectors. I burnt a chip to compensate for the larger injectors and it worked for a a couple weeks before the mass air broke. I can't pull any codes because I need to run the serial wire from the comp to the obd port. I have 2 maf sensors and they do the same thing, tried a diff comp and memcal. Anyone have any ideas? Also pinout C on the mass air that runs to the computer, how much voltage is suppose to be there when the ign on?

did you try setting your minimum air?

Yes I have. I made sure that the IAC was all the way in and nothing in its way. Unpluged the sensor so that the ecm could not adjust it anymore and still does it. there are no vaccuum leaks as I can smoother the car by putting my hand infront of the intake.

when i had that issue, it was due to the harness/plug. i pushed the wires up, the idle dropped to 700.. pushed the wires down 1500rpm. was hell on my transmission till i figured it out.

Are you talking about the MAF plugin? Also is anyone able to tell me how much voltage is suppose to be on pinout C on the MAF?

yeah.. the maf connector itself. I think it purely had to do with age and corrosion inside the plug. one way it was making good contact, the other it was not. I scored a new connector, cut the old one off, and soldered in the new one. the connector i got from a sponsor of this site that sells a mess of different plugs and harness pieces. can't remember the name though

That is basically what I did too. There is a new connector on the car and it worked for a week. I think I may have found the problem but not sure. I connected a voltmeter to the signal wire on the maf and grounded the other side. I get 5V when the ign is on and the car is off and maf disconnected, and 2.5V when the ign on and car off. I tested another car and it had the same thing. Now I tested while the motor was running. On my car the voltage was at 0.6V at 1500RPM and on the other car it was at 1.2V at 1000PRM. Why is there that much of a difference between the two cars and is this normal?

Went home last night and pulled the codes, the only one that was set was 12. Any Ideas?

code 12 is the diagnostic code that shows that your check engine light is working and your onboard diagnostics is working as well. you have nothing to worry about.

LOL i wish I had nothing to worry about. Ya I know code 12 is set basically all the time when the ignition is on because if I am not mistaken that is the dizzy reference code, and it is not spinning so that is why it gets set. Now I have even more weird news. When the car starts I take the battery off and everything goes hay wire. The gauges move however they want, the car hunts for an idle, and then when I put it back on the car idles at 1500 again. Checked all the grounds over and over again. The other thing that I noticed is that with the maf connected the IAC wants to open up to let more air in and that is why it idles so high. Once I take the maf off the intake, but the harness is still on the idle drops and runs normal. What is going on?

Have you tried running it with the alternator disconnected?

I would do some datalogging to check the values being used/seen by the ECM.

Ya I tried with the alt disconnected and it still does not run right. I borrowed a scanner from a buddy and connected it and low and behold he does not have the cartridge for my car. So I have to find one so that I can do that. Any other ideas?

Please don't disconnect the battery while the car is running. Possible to damage at least the alternator also can have high voltage spikes, etc.
In early cars with a "generator" that was a valid test ; if car stayed running then it was "putting out". HOWEVER alternators are completely different..... they can be damaged or cause damage to the modern cars' electronics.
Sorry , can't help with your problem though.

The voltage spikes were noticable but nothing crazy, I had the headlights on to draw the power away from the car.

I am back at square one and not sure where to go with this. put the new alternator on the car and that issue is fixed. but still havehe high idle and stumble. it looks like the high idle is caused by the IAC wanting to retract for some reason, and the stumble looks like the timging is all over the board when you hit the throttle. I need someone to shed some light on this issue, or give me a direction to walk in. Also I tried to put a scanner on the car and for some reason it didnt pull anything jsut kept saying that it was disconnected. I know the serial wire from the ecm to the aldl plug is correct. Is there something special that I need to do in order for the scanner to recognize the car? BTW the scanner is a Snap ON 2500

hows your tps sensor voltage looking at when at idle?

TPS is at .54 volts and increases smoothly as the throttle opens.

I think those two functions (IAC logic and spark advance) both rely on DRP's from the distributor to determine engine RPM.
You could verify the engine RPM by hooking up a scanner or datalogging.

You said unhooking the MAF makes the problem go away, but you've tried another MAF, with no fix.
Have you tried disconnecting the ESC connector so that there is no spark control?

Ya I disconnected the ESC and also put another one on the car. they both check out. I even went to the trouble of seeing if the ESC was supplying the 8-10V to the ECM and it was, it had 9V constant. The Knock checks out as well. Now you said something about a DRP, What is that never heard that abbreviation before? Also I tried to put a scanner to it and it jsut said disconnected. Tested on my brothers blazer and it works fine. Is there anything that I need to do special for this thing to talk to the ECM? or should it interface automatically. The reason i ask is becuase I have seen and heard that with some cables you need a 10K resistor to jump A and B before you can get any info of the ECM.

DRP = Distributor Reference Pulse or Period. It's the trigger signals coming from the distributor.

I think most people buy the $40 cable and use the free software out there. It's in the stickies in the DIY PROM section.

Now I have three questions. First, is the DRP the same thing as the megnetic pickup within the dizzy? Second, if that went bad would the car even start? Third how would I check that? Does it spit out a voltage when cranking? A resistance check?

hrspwr,man i hop someone can get ya lined out on this,cause mine ids doing the same damn thing!!! I know what your going through man!

Ya man it is starting to become a real pain. What exactly is yours doing? Also to the other members. To test the pickup coil in the dizzy, how many volts should it be outputing when you are cranking the motor over? If I am not mistaken it should be ACV.

Ya man it is starting to become a real pain. What exactly is yours doing? Also to the other members. To test the pickup coil in the dizzy, how many volts should it be outputing when you are cranking the motor over? If I am not mistaken it should be ACV. Also how do I test the module in the car?

i have replaced the complete dizzy on mine,and every sensor on the thing,ecm has been replaced also.thought i had a vacuum leak,,replaced intake and runner gaskets.so i have no clue.i have been checking out the stand alone sd wiring harnesses,will probably convert over before doing my engine swap.

To be very honest with you, I am no closer than I was 2 weeks ago when this started. I have checked every sensor on the car and they all seem to check out fine. The only two things that I am not 100% sure on are the pickup coil/module and the Mass air. I have two mass air sensors and they both do the same thing. I am hopefully going to test those sensors on a buddies car and see what it does. The other thing that I am going to do is burn a chip and put a rev limitor in it at about 1500-2000 and see what the car does. IF it hits that and stops, then the pickup and module are working as they should and sending a good signal to the comp. IF it revs past that by a fair margin then its time to replace, I would think. The reason I am doing this is because I cant get a darn scanner on the car in order to see what the ecm does. SO I have to back door it lol

well this tpi stuff is sorta new to me,but i have done the stand alone speed density conversion in a 88 chevy truck,plus i have read that tuning the sd is alot better or easier than the mass air,but i dont know for sure,as i said,its still sorta new to me,lol

do you use yahoo messanger?

It seems that everyone is going away from the problem. When the MAF is unplugged, it idles fine. When the hot wire was taken out and the new MAF put in, did you replace the relays? That is where the problem is if you can unplug the sensor and it runs normal. Replace the relays and you should be fine. By unplugging the MAF, the computer goes to a base setting and uses it because it isn't getting the info it needs from the sensor. So again, REPLACE THE RELAYS! Both the main MAF relay and the Burn-off relay.

How sure are you it is the relays. I have tested them and they work, the mass air is getting the voltage it needs and everything. I even went and bypassed the relay and gave the mass air 12V to see if it was and it does the same thing. Now, do the power relay and the burnoff relay rely on each other to work? As far as I can see they are good

i had similar problems,found that some dumba$$ had jammed a test light in all the connectors including the ecm plugs ,car would do all sorts of weird stuff,i replaced every sensor,the ecm and module and distributor and after a short while the gremlins came back................always probe from the back of the connector.......anyway i had to pick up a standalone tpi sd harness.and now it runs better than new.<<<<<<<<<<<< i have been all over the forums and all these problems are with maf cars,all very similar complaints.>>>>>>>>>>>the 7730 sd ecm was used in a lot of other cars and is smarter faster and more reliable.also i had trouble with reman maf being out of calibration.

http://www.larryselectricsite.com/TPIKIT.html $375 new harness,ecm and prom.

How did you test the relays? Just because you here them click doesn't mean they are good. Think of this. When the leaf took out the hot wire in the MAF, it did something to the circuit. Unplugging the MAF shows there is something wrong with the circuit, not necessarily the MAF itself, but something with the circuit. The ECM goes to a default setting with this sensor unplugged. Relays are a known weak point in the circuit. The relays may test ok when you put power to them, but if the circuit is not complete and you are doing a voltage drop test, you will always see 12v. When hooked up, what voltage do you see coming out of the relay when the car is running? The relays usually cause the MAF to do this when they have high resistance in the contacts when activated in the relay. This is how I know the relays may be bad. I also have my ASE in this with a 2 year associates degree in automotive, diesel and industrial technology. Use a volt meter and not a test light on computer controlled circuits. Try testing it the way I described and you will find your answer.

I have already tested the relays because there is 12V when the car is running and I even took the relay out and put 12V to the maf itself with the same result. I always use a voltmeter when testing circuits, the only time a use a test light is for circuits that I want to know if there is power, or if the cuircuit is suppose to illuminate a bulb. I ordered the relays yesterday and should be in today. I really hope that is the issue because this is becoming a big pain in the arse.

Hey guys, I think that i may have found the issue with the car. I noticed that when the car is running at 1500rpm the maf voltage is about 0.6V. when I took a look at the bin I was using that voltage, the maf says that the car is flowing about 6-8g/sec. When i matched that up to the Max airflow table it looks like the car under 500rpm, and that is why it wants to increase the idle. I am going to mess around with the tables a bit and see what that does. My question is, why would two mafs do the same thing and be out so much? Is there another way to calibrate the maf and not the bin?

stupid question, but does this MAF you're using have the screens in place? just a though, there IS a reason why people pull those screens out.. though not always the smartest.. second though, how the HELL did a leaf get in there, no filters or something?

Not stupid questions. The maf that was on the car, the person that had it before me took out the front screen and left the back. A leaf got in there because I had the car running and i took the air lid off to see the filters. I guess it got in there at that time. Now, why the hell is my maf only reporting so little airflow, even tho there is tons of air going thru the darn thing? Replaced the relays, the maf is getting 12V, the ground is good, the signal wire is good, the analog ground is good, burn off is good and works, all seperate from eachother and no shorts, no codes set by the ecm. The maf is reporting .6V at 1500rpm which is about 7grams/sec and should be about 76grams/sec, 10x the amount of air. Anyone? Maybe one of the guys from the tuning section can help me out here

After two weeks of bruised nuckles and lots of profanity, I found the gremlin. I bought some pigtails to replace the old and broken ones that were on the harness when I got the car. The IAC harness was the worst. I soldered two wires backwards because as I cut one I soldered it in, well the person before me had them in backwards too. The one thing that I dont understand is the car ran for 2 weeks prior to all of this happening. I still have an issue though. Still has that stumble/misfire. Mostly does it when the motor has a load, but does it a bit on idle too. The more I run the car the worse it seems to get. I am going to start with teh basics, wires, cap. rotor.....Any other ideas?

ohm out your injectors, may also have an issue with your ignition control module

I tested the injectors before, they are all at 15.9-16.1, but I will do it again. Ya i think it might be the module because it seems to only do it when the car starts to warm up and mainly under a load