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Old 12-12-2010, 09:47 PM
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1992 K15 Blazer Help!!!!

Hey all, my 92 full size Blazer is giving me hell. Its a 5.7 tbi with 700r4 4x4
Im getting a loud hissing sound from my tbi and it coming from the iac
my check engine light is flashing rapidly when the key is just turn to the on position and also when the motor is running. I pulled the codes and im getting the 12 code which is normal and Im getting code 51 which is faulty prom. The truck idles very high(1200-1500rpm) and when you stab the gas it stumbles and bogs almost completely out. Its almost impossible to drive it, seems its getting too much air or gas and just bogs out when you try to get on it. I have change fuel pump, filter, EGR, IAC, and TPS and have had no luck. Im completely ignorant when it comes to these computer control vehicles. any kind of help will be surely appreciated

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Old 12-12-2010, 10:49 PM
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Check powers and grounds for the code before replacing parts...the hissing could be plugged exhaust and would explain the lack of power. Hope this helps.
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Old 12-12-2010, 11:26 PM
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hissing

did you follow the instructions for the AIC adjustments when you installed it?
It's not an R&R item. Just like the TPS, if you don't get it right, it won't run right.
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Old 12-13-2010, 05:38 AM
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Well I know its not plugged exhaust because it has brand new exhaust.
I did not adjust tps or iac when I installed. Could it be that the ecm or prom is bad and isn't comunicating with the Iac? I am getting the 51 code. Also the temp gauge isn't working inside, would this cause system to malfunction as well.
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Old 12-13-2010, 05:51 AM
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The computer adj. from info acquired from all sensors including the temp.
When the engine is cold it needs more fuel AND air. Info from the TPS,02, temp, MAP, EGR, and rpm are all a factor in the operation of the IAC. After the engine warms up, the comp. goes into closed loop and should idle down.
On open loop the hissing is normal but it is more noticeable when the air cleaner is off.
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Old 12-13-2010, 06:05 AM
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The thing is even after the engine runs for 15 mins its not idleing down, and when you try to drive its like its getting too much air or fuel. It bogs down when you try to press the gas. I just went out and removed the ecm.
it say service no. 16146299 awld. Im going to try to pull the prom out clean it and see what happens.
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Old 12-13-2010, 06:12 AM
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Check for vacuum leaks............
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Old 12-13-2010, 06:15 AM
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Ok, why is the checking light flashing fast.
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Old 12-13-2010, 09:32 AM
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they normally make a loud hissing sound if you take the air cleaner off.

I'm guessing that you have a '299 ecm in that?

Did you mess with the prom? Your flashing light and high idle is it being in limp home because of either an ecm or prom problem. If you messed with the prom, pull it out, pop it out of the carrier and make sure all the pins are straight. once you have them straight you'll want to spread them _slightly_ wider than they want to sit in the carrier (maybe about a 1/16" total) and pop it back in. when you pop it back in it should sit with all the pins firmly pressed against the plastic seated in their grooves, if any aren't fix them before trying to seat them back in the ECM.

If that doesn't fix it I would check to see if there are any bad grounds (easy way is to just attach one of the ecm grounds to a known good ground since they're all strapped together inside the ECM), but you probably have a bad prom or ecm if straightening and reseating the prom doesn't help. They can be tested but you probably wouldn't be asking this question if you had what you needed to do that.
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Old 12-13-2010, 10:18 AM
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Quote:
Originally Posted by Elkyblack
Hey all, my 92 full size Blazer is giving me hell. Its a 5.7 tbi with 700r4 4x4
Im getting a loud hissing sound from my tbi and it coming from the iac
my check engine light is flashing rapidly when the key is just turn to the on position and also when the motor is running. I pulled the codes and im getting the 12 code which is normal and Im getting code 51 which is faulty prom. The truck idles very high(1200-1500rpm) and when you stab the gas it stumbles and bogs almost completely out. Its almost impossible to drive it, seems its getting too much air or gas and just bogs out when you try to get on it. I have change fuel pump, filter, EGR, IAC, and TPS and have had no luck. Im completely ignorant when it comes to these computer control vehicles. any kind of help will be surely appreciated
A loud hissing sound would certainly make one suspect a vacuum leak. If form the IAC it's most likely in that area. Code 12 is basically the system saying it checked itself and finds no computer errors, i.e. "you can trust me".

The high idle makes it sound like the IAC is bypassing too much air. This is a pretty complicated circuit and could be reading something else wrong such as believing the AC is on when it isn't. The IAC goes thru a bunch of steps to achieve and maintain idle under several operating conditions. One of these is that it parks itself after the engine is turned off. A constant high idle sounds like for what ever reason it isn't doing that which is prbably also causing your furious blinking CEL light when you put the key in as the computer does keep track of what position the IAC valve is in.

This system is also sensitive to battery voltage and hence engine grounds and general cable and wiring quality including a host of connectors.

Code 51 is saying that either a sensor or the computer itself is having problems, That's a pretty general code. I'd run the engine idle speed up manually and disconnect the IAC to see if it sets a code 35 that would tell you whether the computer is watching that thing. There is a plug on the side that has an idle throttle plate set screw, knock the plug out and you can plan with the throttle plate position to keep the engine running with the IAC out of the circuit.

Bogie
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Old 12-13-2010, 01:25 PM
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Code 12 means that it's detecting the condition that you set that let you read the codes (in other words, if you're reading the codes you're seeing a code 12 no matter what)

Code 51 means that the ECM cannot read what it expects from the PROM (chip)

the IAC _IS_ a vacuum leak, which is why it sounds like a vacuum leak

Unplugging it will prevent the pintle from advancing so you will likely have a constant high idle. When you turn the key on, it advances the pintle till it bottoms in the seat and then backs it off a set number of steps according to the programming in the PROM till it starts, then once it sees an RPM over 250 it will assume it's running and advance/retard the IAC pintle till it gets the idle called for in the prom. Turn the key on wait a second and then unplug it you'll also see a high idle, since once it calibrates itself (advances the pintle to the seat) it opens the IAC enough to act like you partially holding the throttle open.

You can unscrew the IAC, advance the pintle by hand and screw it back in, but if you screw it in tight enough to force the pintle back you can damage the IAC (they usually talk about wrecking the motor in it, but usually what happens is that the threaded section breaks off), so that is not a good way to test it. There is a dealer tool that looks like an odd shaped foamy ear plug that drops in the IAC passage and blocks it off.

All this doesn't matter, the ECM can't read the prom, setting a code 51 and is putting it in limp home mode (basically a high idle, some medium timing and fuel setting, supposed to get you home when things are AFU, but often the car doesn't run well enough to do that), and NONE of the rest of this means anything till you figure out why. It is acting correctly for when it can't read the programming on the prom.
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Old 12-13-2010, 01:30 PM
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Unless you have the test pin grounded, the flashing CEL (check engine light) means it's in limp home mode. If you have the test pin grounded then the flashing light indicates warm up mode, and once the O2 sensor is warm it will flash 1x per second at and a/f ratio of 14.7:1 (stoich) and faster or slower depending on how rich or lean it's running.
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Old 12-13-2010, 02:21 PM
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Ok heres the deal, I went to the bone yard today and found another ecm.
My original ecm is service no. 16146299 AWLD and the one I picked up was
service no. 16146299 AWHC. BTW this ecm came from a 92 Van with 5.7
I put this new ecm in and checked it for trouble codes and it only gave me code 12. So I tried to start the truck and it wouldn't start at all. So I put my original cpu back in and it started but ran very poor. I took the prom out of the bone yard ecm and put it in my original and check the codes and it only showed code 12 when before it showed 12 & 51. I tried to start and it wouldn't start. So then I put my original prom inside boneyard ecm and it gave me both 12 & 51 codes, tried to start and it would start and run for 1 sec then die. Does the AWLD and AWHC at the end of service number means they are completely different. This thing is driving me crazy and I dont know what else to try. Please help!!!
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Old 12-13-2010, 03:46 PM
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You should get a code 12 entering and exiting diagnostic mode. First code12 then code 51 for trouble and then code 12 again. My old Dynasty mopar did the same thing with 3 turns of the key to enter diagnostic mode but a different code #. Most onboard computers operate in the same fashion when entering diagnostic mode. Have you priced a new ECM yet? I've heard of sticker shock on some model's but a buddy of mine had problems with his Buick this summer like yours and got 1 new for only 100 bucks at AZ . I'll bet you've spent more than that already and it still ain't right. The computers have to be a direct match to be compatible with the sensors by the year of the vehicle and model because of emissions standards which can be different for different vehicles. One wouldn't think it would be that big of a deal being that your engine and year are the same as the van BUT, that's why the ECU has different #'s. At this point if I were you I would break down and take it to a good garage and be done with it instead of throwing more money at it.
I've been through this with my old 88 F-bird 5.0 EFI. so I can relate to what your going through. Hope this helps some. I'm surprised Latech hasn't jumped on this one as he is schooled on stuff like this pretty well.
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Old 12-13-2010, 05:12 PM
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I called tbichips.com this evening and he said the ecm I took from the boneyard was actually a ecm from a 5.0L van, he stated that if I did use that prom in my computer it should have ran. Maybe you're right It would prolly be best if I take it to a garage. Thanks for all the help
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