If that goes to your MAP sensor, then yeah that could be a BIG problem but judging by the 1-way valve in that vacume line it's probably vacume for your accesories. This leak will cause a slightly high idle if the IAC can't close enough to compensate. A vacume leak of this nature just acts like you opening the throttle blades slightly more.

I wish you would get some real diagnostics done. Either barrow a laptop and do some datalogging or pay a shop to hook up a snapon scanner. There is something major going on and if you know what your doing your ECM will tell you exactly what it is.

 

yeah its going to the shop at the begining of march if i can swing it and have them tell me whats up. How much is a scanner? If i could i would just buy one if they aint too much. Im not sure exactly what the hose goes to but i know that it goes a few different places. I will take a look tomorrow.

 

On my 88 Form. The hose you circled goes to the heater/AC/vent
controls. I also have a Y fitting before the brake valve and I think that hose used to go to my cruise control (which doesn't work and never did since I've owned it) that I removed.
I know it doesn't go to your MAP because that hose connects to the back of your TB .
Still good though, you fixed a possible vacuum leak!

 

If you have a laptop, or you can barrow one, you can get a cable for less than 50$ ready to go, or make your own for 10$. WinALDL is free, and does more than a snapon scanner could ever dream of.

Like I mentioned earlier, with a MAP based system a vacume leak really doesn't matter. The MAP sensor will see the change in vacume in the intake and compensate for it. The worst problem it can cause is a high idle if the IAC can't cycle down far enough. While were discussing it, your IAC is nothing more than a controled vacume leak around the throttle butterflies.

 

im taking your advice monte. I have a laptop but the battery dont work. I have winaldl on my computer and some other one also. I know a little bit of electronics so im gonna make the cable whenever i run over to radio shack and get the connector. I have the resistors and transistor. If i just run the car at idle will it tell me what is going on wrong or am i going to have to buy a power adapter or an inverter to drive around with the laptop and see. Thanks for all the help so far also.

 

Just hooking up to the ECM with the car off will allow you see whats going on with most of the sensors. Once you get hooked up slowly sweep from idle to full throttle (with the car off) and watch your TPS readings for dead spots or wacky readings. Also take a quick look at your coolant temp, if your sensor goes screwy it'll usually read really low like -20 or somthing in that range. Your car will run but will be drowned in fuel. Winaldl will also let you check the codes. With the car running you can see what your map readings are (should be in the 30-40 range at idle) and make sure your ecm is getting a good clean RPM reading. I had a coil go flakey and my RPM readings would go haywire whenever the miss would happen. If absolutely everything looks fine then you may have to do some driving around and see which way the O2 sensor dives when the miss happens. If it dives lean, you have a fuel delivery problem, if it dives rich you could have an ignition problem. If you can get the miss to happen while power braking then you should be able to get a good snap shot of whats going on without driving the car. Also keep an eye on your knock sensor, it may also point you in the direction of the problem.

You'll be able to rule out a lot very quickly by datalogging. Let us know what you find, and feel free to post a log of the problem. We can probably get you pointed in the right direction pretty quick with a good log of the problem.

 

well here i am already to go out and do it and i just looked at my laptop for the 9 pin connector and my computer dont have it. I didnt even think to look. I feel stupid. Is there any other way to hook it up? I have 4 usb ports and IR port 2 of the firewire ports. S video and the 16 pin which i think is for a monitor. I cant believe this. Got my toolbox out to make the cord and everything. Hopefully there is something else that i can and get this to work.

 

nvmnd. I went out and bought a usb to DB9 connector cable. Hopefully this will do the trick. I really want to try this and see what comes up. I will be letting you know.

 

There you go Don't forget to set Winaldl up for you ECM (746). Also make sure your using the schematic that doesn't require the external 12v source, you shouldn't need it, and make sure you leave out the 10K resistor between A and B our ecm's don't need that. Just some newbie mistakes I see happen alot. Good luck

 

alright this is what i got and hopefully i got what soemthing i can use. I didnt throw any codes. My rich flag was flashing in and out every few seconds or so. the idle/cool flag was on. But anyways the tables. Well i dont know how to make the files fit because i saved all the files but they are going to fit. Do you know how i can make it viewable to everyone. I didnt have anything show up in red either. I only did it at idle because i dont have the means to take the laptop around with me yet. How do i do it from here. Can i open the files with a different program or make a link accessable to anyone. I just dont know how to do it but i think that i have all the info.

 

Two things.

First, the IAC is a vacuum leak, yes. But you still want to minimize its use if you can, because the more air flowing through the IAC, the less air there will be going by the throttle blades, and in TBI, that's one of the mechanisms that aids fuel atomization.

Second, you said if you get a miss, and have an ignition problem, the O2 will read rich. It's the opposite. It reads the fresh O2 (unburned or partially unburned fresh mixture, which includes O2) as lean. To prove my point, when my #7 plug wire was shorting to my exhaust manifold, causing a miss, my O2 sensor read low and my BLMs shot up.

 

i guess i will do it like this. I saved the file in a wordpad and i will just write the numbers down.

1st number i guess is time. Goes up at 1.2s intervals
2nd number alternates from 128 to 132
3rd number reads 8 all the way down
4th - 173, 5th - 15, 6th - 39, 7th - 0
8th - anywhere from 60 to 66, 9th - bounces from 23 to 26
10th - 35, 11th - 142 up to 144
12th - varys from as low as 66 to 118, 13th - 0, 14th - 0
15th - 0, 16th - either 130 or 194
17th - anywhere from 134 to 137, 18th - 130, 19th - 19
20th - 150, 21st - 126, 22nd - 2221, 23rd - 14 or 15
24th - 206.8 up to 208.9, 25th - 0, 26th - inbetween 32.9 and 34
27th - from 575 to 625 (RPMs), 28th - 3.6, 29th - 144
30th - low .3 to mid .5's, 31st - 13.4 - 13.7, 32nd - 19
33rd - 150, 34th - 121.8 up to 124.5, 35th - 0
36th - 0, 37 - either 1 or 0

I dont know if this helps (hopefully it does) All i did was save my log file and open it in notepad and read the numbers across. Maybe tomorrow i will just write them down. I will try and get back and check it out tomorrow. Maybe someone can tell me if this looks ok. Thanks

 

hey monte, where can i get a winaldl cable from ready to go?

 

Here's a copy of my last WinALDL log for reference. Note that the my LO3 still had a few minor problems at the tim eof this log, but ran pretty well most of the time. I've edited the header at the top of the file to make it easier to read. To take advantage of this, open the file in WORDPAD and set the program to disable word wrapping (View --> Options --> Rich Text --> No Wrap).

I've renamed the file with a .bmp extension. First, rename it to .ZIP and then extract it with Winzip, WinRAR, 7-Zip, etc...

 

it wont let me rename it to a .zip file. Maybe i am just confused. Maybe you could tell me a little more. I would like to see how your table looks.

 

I think i got this now to where i made my own table and can put it on here.

 

sensor data

 

As for the flag data and im not sure if that is needed or not but it is as follows
BLM enable
idle/cool
reference pulse occured
closed loop
rich flag
air divert solenoid on
no a/c requested


i think that is everything. Let me know if you can tell me anything by these numbers. Hopefully it says something.

 

Huh...I replaced my battery today because it's been on the edge of dying for the last year. It's always read the proper voltage, but didn;t have the current to support anything properly. I went out to start the car today and it would only click. The voltage had fallen to 11.77V. I replaced it with a decent 850CA battery from AutoZone and the ride is MUCH smoother now from idle all the way up to 6500RPM. It pulls much harder at any RPM and the exhaust smells a little better now.

Please note that I've had this battery checked and everyone says it was OK. I knew otherwise. It just didn't act right. For a quick check, you could swap a battery from another car in to see if it helps. It's a shot in the dark, but worth a try. Chances are you have multiple problems and you're locating & fixing them one at a time.

Also check that the "stove pipe" on your air breather snout isn't stuck in the "cold start" position. Just remove the snorkel from the breather and look down the end. You shoudl be able to see all the way to the filter. If that little trap door has stuck shut it would be just another problem, but easy to check & fix.

 

im not quit sure where you are talking about. Just kind of learning as i go. A little more detail would help and i will def. check that.

I think that my battery is ok. In the winaldl program it said it was reading high 13's or 14. I was also reading and from what i understand with the BLM at 128 that is right where it is suppose to be at least for idle. Im also guessing from what i read that the other numbers look alright except for the IAC. i think i read somewhere that about 10 is the number you should be reading but im reading 14 or 15. is that high and if so whats that mean.

Im trying to get it so i can put the laptop in the car but the laptop battery is dead. Trying to figure out a cost effeciant way to hook it up so i can run it and check it out.

 

I am going to try changing the battery also. Actually have one downstairs from a car that just recently got junked and battery was pretty new. Maybe try that in some short time.

 

Best case scenario is for the BLM = 128 at all points. As for the computer datalogging, you can run most notebook PCs off of a 100W power inverter. Should be able to score one new for ~$40. Just look at the power supply input rating. Multiply the volts x amps to get the power inverter minimum rating, but 100W should be more than enough for pretty much every notebook PC.

What I meant when I was talking about the "stove pipe"...On an LO3, if you look at the air breather from the top of the engine, it's circular in shape. There is a metal "snout" coming off of it which connects to a plastic "snorkel" which then leads to the front of the car. Completely ignore the plastic part for the time. If you look at the metal snout, there is a tube coming off the bottom which heads down to the exhaust manifolds. There is a thermal sensor in the air breather itself which operates off of intake manifold vacuum and lets a flap inside the snout flip to an open/closed position. The whole purpose of this is to divert warm air (warmed by the exhaust manifold) into the throttle body in very cold conditions. Once the engine warms, the flap changes position and blocks the hot air from the exhaust manifold and only allows cool air from the outside into the engine. If the flap gets stuck in the "warm" position, the engine will still run, but poorly because it will be intaking hot air from around the exhaust manifolds. This may or may not make much sense now, but just look underneath the metal snout and you'll see what I'm talking about. If you remove the plastic snorkel you should be able to see all the way up it to the air filter. NOTE: The thermal sensor in the air breather can also be another source of vacuum leak if it's plastic line is cracked -- another one to check

My battery always read perfect on the volts (i.e.: always between 12.5V & 14.7V -- depending on a variety of conditions), but didn't have the ability to supply an ample current for the engine. It was enough for the engine to start and run, but just didn't operate very well. This confuses the living crap out of me because it takes A LOT more current to start the car than it does to keep it running. The car always started (slowly, though), but because it started at all, I would expect it to keep running w/o a problem...whatever *severely confused*...

To rename the file to .ZIP, you can do that through DOS by issuing the command "ren log.bmp log.zip" or you can do it through Windows Explorer, but you'll have to show file entensions first. To do this in XP, open Windows Explorer and click the Tools menu --> Folder Options --> View and uncheck the box which that says "Hide file extensions for known file types". Hit OK a few times and now you should see all the file extensions. Simply change the .bmp to .zip and you're ready to go. I'd suggest rechecking the box after you're done to avoid accidentally changing a file extension when you don't mean to.

 

Your BLM's are very good, most stock vehicles aren't that close. Also your IAC is a bit low for stock, I know you read that we shoot for about 5 to 10, which is true, this helps to keep the IAC from being able to alter the idle too much. Stock usually runs around 60 to 70 counts when warm. I say yours are low due to the vacume leak you found. Nothing really jumps out at me with a big red waving flag. Which means it's an intermitten problem. These are harder to diagnose. Didn't you say you could get it to miss when you power braked it? If you can get it missing for a few seconds that should get you enough data to see whats going on. It sounds like to me your chasing an ignition glitch. I did the same for months, it ended up being a ground screw inside my distributor.

Check out walmart for that power inverter, they are around 30-40$, and very usefull for other things besides datalogging.

 

im not really sure what powerbraking is. I havent been able to drive the car around yet but im hoping that i can a power inverter shortly. Maybe even today. Im hoping. There is a 400 watt inverter at home depot for $40. Im thinking for the dollar that is the best bet.

The only thing with the problem is that it never really cuts and in and out. After the car warms up and get driven around for a minute the violent jerking happens when accelerating. It just wont go away after that. It always runs good when its really cold. After it warms up its bad. I can see where it would make intermitten contact and maybe cause a short to ground and make it cut in and out causing the violent jerking but wouldnt it do it while it was cold too?

 

power braking: The act of simoultaneously appying the gas and brake to load the engine.

 

Have you pulled/checked/changed your plugs yet?

 

A vacum leak would cause the IAC to be low???

If so, why when I unplugg any vacum hose the car revvs up???

I think violentgod is going a good thing here. I think there must be some kind of wiring glitch or something??

What kind of shop could check this???

 

A vacuum leak will definitely make your IAC counts low. The ECM has a table that it references to get a starting place for the IAC upon startup. It then constantly watches the RPM and references another table called the “desired RPM” table. If the idle is not within 25 rpm (this constant is changeable too) of the desired RPM then it will remove or add IAC counts till the idle falls back into line. Soooooo, if you unplug a vacuum line, then your idle will shoot up, then the ECM will start closing off the IAC valve until the desired idle is reached. The only time it won’t get back to the desired idle is if the IAC bottoms out and there is no more room for adjustment. This is also where having too low of a thermostat is a bad thing. In some cals 160 degrees references a higher idle than 190, so your car may not idle the same with a colder thermostat….not that this has any bearing with what’s going on here.

Back to the problem at hand, you say it doesn’t act up until the car is warmed up. This probably means the car goes screwy once you enter closed loop. In closed loop the only sensor that the ECM looks at that it didn’t in open loop is the O2 sensor. Have you replaced your O2? These sensors may look good on the scanner, and the ECM thinks it’s getting a correct signal, but in reality the O2 is skewed either way lean or way rich and still flipping back and forth across .450 volts like normal. Most of the time O2 sensors just get unresponsive, but I have seen them just “go lean”. You could also have an exhaust leak up stream of the O2 sensor, this will also mess with things. The popping and jerkiness you describe sound like a lean condition. A rich condition is usually characterized by a bog followed by the engine clearing out and continuing to rev. Ahh but you describe the miss under heavy to full throttle, which is when the ECM enters Power enrichment mode (PE), in this mode the ECM ignores the O2 sensor because it’s only accurate at 14.7 to 1, if your blm tables are skewed to the lean side of things, the ECM will use this correction to likewise richen up your WOT mixture. If your BLM’s are rich, the ECM will ignore them at WOT.

As you see your problem doesn’t appear to point to a sensor problem, which makes me think you have a mechanical problem. I.E. coil, bad ground, or intermittent fuel pressure problem.

 

i can never get up to full throttle. As soon as it starts jerking i let off the gas because if i give it anymore it will probably stall. Not to mention if it doesnt i dont want to get whiplash. I wish it would warm up a day or 2 in here so i could check some things. As the car gets warmer the worse it gets until it just really doesnt want to go.

 

It sucks, but that's a good thing because the problems will be easier to locate.

Did you ever get around to checking the timing?

 

Hey there. I have not back all the way thru your posts, but how is your EGR system? Valve, solenoid, etc???

Weird, but aftermarket EGR valves SUCK for our F bodies. The ones you have to take your OE number and find the correct washer to fit the EGR valve!!!

you have seemed to have done everything else, but please check the EGR system completely. Had two mechanics that i talked to about my car and mentioned your issues and that is the first thing they said to do. REPLACE WITH OE. You can get it off of GMpartsdirect.com for about $61 includes tax and shipping/handling.

Good luck. I will try to read back to see what you have done and then see what i can do to assist.

 

Is your vaccum still at 17 psi???

 

$61 is not bad at all, because when I went to replace mine *Twice...Grrr* I got the Borg Warner for $70 and I still had to do the stupid metal washer thing.

OE & OE-type are sometimes just different enough to be a pain...like O2 sensors...

I saw that he had 17" vacuum, but that was with the leak. I was wondering if it's possible to do a vacuum check on the entire intake menifold for leaks? I haven't gone through the valvetrain geometry to see if it would work, but it may. Now I'm curious.

 

To be honest i am not sure if you can check the entire intake vaccum pressure. There are several vaccum lines on the intake, but if there is a leak whether on the throttle body lines, intake or intake gasket, etc than your pressure would be less than 20 no matter what. Am i correct?

i am getting ready to replace my O2 sensor with a Bosch. Any known problems with them?

 

Oh, yeah. Out of all the OE-type replacement parts, I've never heard more complaints from anyone (including myself) than on the Bosch O2. Please, please, please get the AC Delco and be done with it. Within a few weeks, my Bosch was half-dead and I hear this all the time.

One possible explanation is that I've been told it's slew rate is MUCH faster than what the older GM ECMs were designed to deal with so every time the ECM take a reading of the O2, it's in the process of a cross-count and is inaccurate. The Delco O2 sensors are supposedly much slower and it's almost like an averaging of the O2 samples when the ECM checks it.

 

LT1 PCMs, which are light years faster than these TBI ECMs also hate anything except GM O2 sensors, so I'm not sure about that one...

 

Should there be vacum at idle???

On my car there is none on idle or when powerbraking!

Its normal in park 17hg (i think its HG).

 

Yes it is in./Hg. Anyway the normal vacuum pressure reading is:

idle: a steady reading from 17-22 in./Hg. Should be closer to 20, but 17 is bare minimum acceptability.

So does the needle stay steady or does it fluctuate at idle? If it fluctuates then from what to what?

Does is fluctuate as idle/speed increases? If so from what to what?

So, in a nut shell what happens to the needle under different idles? Check the pressure consistantly for several minutes and watch the gauge. Slowing increase the idle as you watch the gauge. Check what it does and then watch it as the idle decreases.

Let me know!!!

 

The idle is sometimes steady, and mostly jumping about 50-100rpm. Its not jumping, but more so going from to, and back.
It idles at just under 600rpm, and jumps to 500 and up to 600.
When given gas the car has no jump in tach and its smooth up the RPM's.
With the HI-6s the tach is jumpy during start up and idle can be a bit jumpy. However the car runs much better with it.

I don't mean to steal the thread, I just think both the poster and I have the same problem.

 

Vacum< nope! vaccum< nope! Vacuum>right! Without it, your motor wouldn't be running.

 

Basically, what i am asking is the vacuum pressure reading fluctuating. there are about 5-6 different causes of vacuum flucuations.

1. Needle on vacuum gauge fluctuates from 15-20 at idle suggests sticking valves or ignition miss.

2. lower reading around 15-18 or so but steady pressure gauge readings may suggest late ignition or valve timing, sticky throttle valve, leaking carb or manifold gasket.

3. a needle that drifts may indicate improper carb adjustment, minor intake leak at carb/throttle body or manifold.

4. Needle on pressure gauge vibrates excessively at idle, but is very steady as engine speed increases suggests worn valve guides.

5. Needle fluctuates as engine speed increases may suggest a plugged cat, weak valve springs or leaky cylinder head gasket.

So, vacuum can be present but low, fluctuating etc and THIS CAN be an indication of the status of your engine. Obviously, no vacuum and your car would not run.

Again, please check your EGR system if you already havent. If you have an aftermarket EGR valve take it off and put a .40 caliber bullet in it and it may work better, LOL!!!!!!

Seriously, your EGR valve MUST BE GM OE. Your O2 Sensor MUST ALSO BE GM OE. our cars HATE aftermarker O2 sensors and EGR valves.

I have spent hundreds on diagnosing mine and having same issues as yours in the past and it was my ****ty autozone EGR valve and Bosch O2 sensor. Who would have thought!!!

GOOD LUCK.

 

is there a way to check the egr and o2 without just replacing them. Im pretty sure its not my wires becuase i have had a bad wire burnt right through and this feels totally different. My car would at least acclerate when i gave it gas. It may have been slow and shi**y but it did it. It is really hard to accelerate with the car like this witout it jerking and feeling like it wants to stall. This is much more violent. Is the IAC how you read your vacuum pressure or do i need to get a gauge to read it.

I dont mind at all hellraiser

 

you will need a vacuum pressure gauge. Get that from autozone, etc. All you really have to do is unplug any vacuum hose leading into the intake and connect it to your gauge. I check mine by removing the vacuum hose that is connect to bottom of air cleaner. It's the one that runs from the front of the throttle body to the air cleaner. That should be fine.

Also, take some carb cleaner/break cleaner and spray it at base of throttle body while car is running and around every intake bolt and around where the intake mounts. If the car changes performace (wants to die while you are spraying it in those locations) then there is a vacuum leak there. Obviously, car must be running and dont spray cleaner into throttle body to test vacuum. It obviously will change performace.

That same gauge has the ability to check your EGR valve as well. you can remove the vacuum on the EGR valve while car is off and pump it up with your gauge and see if the vlave holds pressure or not. Another simple way of testing EGR is by seeing if the EGR diaphram is moving freeling while the car is off. Simply reach under the EGR valve and place your finger in one of the holes as see if the diaphram moves freely or if it is stuck. If its stuck simply replace it. Dont go thru the trouble of trying to clean it.

If you need a new EGR valve the BEST place and BEST price believe it or not is GMpartsdirect.com. Awesome site and it's OE.

Your O2 sensor can be tested but you need certain equipment to do so. It's usually tested by making the car run lean by removing some vacuum hoses and seeing what the O2Sensor does and then making the car run rich by shooting some carb cleaner in throttle body and again seeing how the 02 sensor responds.

Best to have a cert. mech test your 02 sensor.

 

Well i went and checked to see to see if the diaphram was stuck or not and def was not moving. So i guess at some point i will have to try and get a new egr valve. Maybe in a week or 2 because i am broke.

have you tried this already hellraiser? I think i was reading on one of your other posts that you have replaced this already.

 

If your EGR vlave diaphram is not moving/stuck then replace it. It will cost you about $60 from GMpartsdirect.com. You can try cleaning it/soaking it with break cleaner and then see if it works better.

Just found out that O'riley Auto Parts has Borg Warner EGR valves which are DIRECT OE replacements for our f-bodies. Come to find out that Borg Warner makes them for GM, lol

Good Luck!!!

 

so when the cars not running just sitting there the diaphram should still easily move inside the valve? I also read that the egr port be clogged can cause the same signs of a bad egr vavle. Yeah it looked to be 62 shipped from gmpartsdirect. Can the egr valve cause the car to run this bad. That violent jerking during acceleration. Either way i think the egr valve is bad.

 

I doubt the EGR alone is causing that. Though a non-functioning EGR will give the same symptoms as too much part throttle spark advance. If, however, you also have a problem at WOT then the EGR is probably not to blame.

Also, you should try to press the diaphram with TWO fingers, one on either side of the plunger rod. Even a new valve will be hard to move with one finger on one side of the diaphram because the rod binds internally. It's just not meant to open that way. Even with both fingers, it will take a firm push.

 

I got it to move but im pretty sure it was stuck because it took a whole lot to move it when i got it out but then it started moving a little better. I dont want to start the car up right away because i moved the TB to get at it and spilled a little bit of gas. Im not sure if its the problem either but it might of been a little problem.

 

also phlaxus - i can see all the way down the "stove pipe". Its open if that is how ya say it.

 

The stove pipe is the part that comes up from the manifold, i.e. the vertical part.