before i forget to ask, what is ECT.

so, for the first time ever, it didnt do it this morning. ran like a boss. go figure. i am not a fan of car games...

i will try to do some of these things later tonight. i will def. have to get that factory service manual, all i have is a chilton. one thought about testing the MAF again, what if i just unplugged while the engine was running to see if idle changes? if it doesnt, wouldn't this mean its not working? i did this trick on another car i had a long time ago, but i dont know if it would carry over to this one. resitance of all the injectors was good, all of em are between 11.7-12.3.

hopefully i will be able to do the scanning next week, and i'm also trying to hunt someone down with a fuel gauge, cant really buy one right now. i've had nothin but horrible luck with my cars this last month and it has wiped out my bank. tax return is already spent too. Pile it on all at once and get it over with i guess.... LOL.

Thanks

 

thanks, I will definatley "Go Nuts"

 

ECT=Engine Coolant Temperature

Did you have the MAF hooked up, when you ran the car that morning?

You might try to unplug the MAF while idling. It may stall, but should re-fire. Should not hurt to try it.

I hear ya, if I didn't have bad luck, I would not have any.

 

Add this
VATS = Vehicle Anti Travel System
ECM = Engine Control Maybe
SES = Service Engine Sadness
SYS = Service Your Sorrow
MAF = Mass Air Failure
Opti-Spark= Optionally Spark

Here are a few feel free to add oradd better suggestions..LOL
It is amazing how clever you can get aftera few 'adult beverages'...
Dave

 

damn, now i feel stupid. just always refered to it as good ol engine temp. yes, i had the maf hooked up. but it did it later that day on the way home so its just continuing with the screwing with me.

did the maf test, it just about died like u said, then started back up and idle'd a little higher, with the fans on of course. injectors flow tested good. suprised they were able to do it as soon as i brought em in, but they are all good. so just waiting for the scan.. man, seems like i been waiting to do that for EVER.

lol. i like these.

 

got a fuel pressure gauge hooked up!! while doing it, it fluxed between 32-35 psi. i still dont have my scanner yet to scan everything else, but thats the fuel pressure. now, i know on my GTP the normal fuel pressure is 40 ish psi, but thats only a 6. if fuel pressure is wrong, would the fuel pressure regulator be an issue? probably not, since it doesnt always do it. just wondering

 

That is too low. My 93 at idle with vacuum line on the Regulator reads 38psi. With the line off at idle it is 42psi.

If I just go to key on, engine off, it reads 42psi. My 93 FSM states it should be between 41-47 psi.

Low Fuel Pressure definitely could cause a lean condition.

The regulator could be an issue, but taking the vacuum line off of it while the engine is running should see about a 4psi increase in fuel pressure.

Did you drive the car with the gauge on?
Did the gauge drop at Key On, Engine off after a short while or stay steady say 5-10 min?

There is a section in the FSM all about fuel system diagnosis. There could be many causes for this.

 

no, i didnt drive with the guage on. all i did was hook it up, start it up, and watched it for a few. it was early in the morning before work, so i didnt have much time to mess around with it, and i didnt really want to drive with it on. call me stupid, i didnt even look at it with just key on, i didnt even think about it. its ok, i already slapped myself for that one... my brain doesnt work much in the morning lol, still half asleep and all that.

i got the gauge from a bud at work, gave it back to him today, but i decided im just gonna go get one of my own, becuase i have needed one in two other occasions, and i know ill need it more. ill pick one up probably when i go get my other car with the scanner that i left in it!!! that was supposed to be yesterday, but there was an issue. very irritating. its too far out of the way to just go to get it out of the car real quick. especially in rush hour traffic.

guess what tho, when i got gas, then got goin again, at about 210*, it did its little sputter. just one little one. probably nothin to do with it, but of course, its playing with my head.

 

You must either live so far from civilization no one cares or you have some serious mojo with the state troopers. in CT 115 in a 65 and it will be a very long time before you drive that car again..

 

At idle, that pressure is too low. Definitely need to look into that.

FYI, it is generally frowned upon to say you where street racing. The mods do not like it as it is against the rules. Save it for Off Topic, if any place at all. Hopefully, your thread does not get locked for your post, as I think it has been helpful for your issue. Being a new member I would hope they would let it slide on this one.

Talk about racing on the track or closed course, you can do that all day.

 

ok. gonna have to do a better job of keeping up with the rules between this forum and the one im on for my other vehicle.

ya, ill look into it. since im getting a gauge i'm gonna do all the checks again first tho. im gonna take a break from this for at least tonight, or until i get my other car back. this stuff gives me headaches every day. i need a freakin break from car trouble!!

4 mile 5 wide bridge across st johns. no places to hide for them. i see people doing it all the time on there. of course, still doesnt make it any better but i had to do it once...

 

ok. got new readings. couldnt go driving with it, cuz the only gauge i could find to buy had like a 2 foot long line. i couldnt rented one for 100 bucks, but this one was 50, and i get to keep it. so anyway:

key on: ~42 psi. guage did not drop at all, even after a long wait. 42 always. while u can still hear the pump running, it would be about 44 psi, but thats not even for 2 secs. then to 42 psi solid.

idle: ~36 psi. regulator line off: ~45/46 psi

giving it gas.. from the engine since i couldnt sit in the car the psi would go up to about 44 then drop to 34 as soon as i quit, but only for a sec, then back to 36ish. i let it idle for a while till it got above 140, nothin changed, gave it gas, and scared the **** outta myself cuz it backfired when i did that. LOL, never had my head and hands in an engine when its done that, so i jumped a little bit. the whole time idling under 140, i gave it gas quite a few times, and a good amount of it, it never sputtered, or choked or misfired. guess it only does it while driving.

so, you said taking the vacuum line of should be an increase of about 4 psi. mine increased almost 10, so does that mean the regulator is bad? if it is bad, why would it only affect it below 140*(the car has only ever done this once above 140, but it wasnt constant or anything, just a one time little cough.

also, bad news for me. my scanner works with obd1. it can read alot of parameters, but ONLY when it throws a code. it records all the info when it puts the code out. i thought i could tell it to do that on its own, but i cant. i dont know anyone that has an obd1 scanner, so im outta luck there. might have to take it in an have em do thier 90$ diagnostic with their scanner or somethin.

 

Ok, based upon that it sounds like your fuel system pressure wise and injector leaking wise is OK. Those pressure and such are fine. Revving it at idle and such will not tell you much. It has to have a load. I got a hose made for my gauge long enough I can tape it to the windshield and drive the car.

Ok your scan tool will not be adequate. You need one that will display live engine data updating constantly as the engine is running.

Like I have said, before, I believe this issue is fuel related. We have narrowed it down some. Since the pump is delivering the correct amounts of fuel (at least at idle) and the injectors are not leaking down. I think we can reasonably rule that out.

Now that leaves all the sensors and such for fuel control, but your going to need a scan tool capable of displaying live engine data and someone monitoring who knows exactly what the data should be and can spot bad data.

If you decide to take it somewhere that has a capable scan tool. I recommend three things:
1. They are either familiar with LT1 engines/Corvettes or have the resources to learn (FSM, etc..) and the smarts to understand the issue quickly.
2. They are willing to actually diagnose the issue as opposed to out parting the issue.
3. You may want to print out our posting here, to help them get knowledge into the issue at hand.

One thing I noticed your car is running rich as evidence by your black tips. This is the only discrepancy between your car and my buddies 94. His did not ever show signs of running rich. You may even want to pull a easy to get to plug and see if they are black/brown/tan? Just to verify.

The scan tool is going to be needed for live engine data, otherwise, your just guessing. You need to be able to see what the ECM is using as inputs for its fuel calculations. As well as commanded fuel injector pulse width.

 

alright, ill look at a plug tommorow. i still havent replaced em(even though i bought new stuff almost a month ago). been waiting till i have time to do the intake and valve cover gaskets.. did change the fuel filter this weekend, made no difference of course.

well, i have yet to find a shop around here that knows corvettes, so, if i did somehow get my hands on a scanner, other then IPW, what specifically would i need to monitor? i know, loaded question. and as far as the things i would need to monitor, would i be able to find what they need to be at in the FSM you were telling me about? (still havent bought one, been spending too much fixing my other car.) i used to have an aeroforce gauge that scanned everything on the planet, man i wish i woulda kept that.

i remember you saying something about these ECMS being tunable, and since its running rich normally, the only way to fix that would be a tune, right? i'm guessing the only place to have that done would be a good vette shop? (not now, just after i get everything fixed, it would be nice to make sure it has a good tune.) i dont think i could buy anything and do it myself, i dont know enough of what i'm doing for that.

 

You said it needs intake gaskets. Are you just chasing an oil leak? Could be an air leak?

1. While in open loop it's gonna run off of a set of values programmed into the computer, good or bad it's gonna run off of them. It completely ignores the MAF and therefore it has no idea where the air is coming from. I might not actually be running perfect, just "good enough" and you'd never know.

2. When it heats up and goes closed loop the MAF suddenly reads VERY low because the air coming into it is not being registered by the MAF. The engine is really getting more air than the MAF is reading, but fuel is being controlled by the MAF and there you have your problem.

This could be as simple as a faulty intake gasket allowing air to enter directly into the cylinder head. It could be a loose air duct between the MAF and the throttle body. It could be a faulty TB gasket. It could also be any one of the millions of vacuum lines on the car!

Essentially there are a million reasons why you could be having the problems you described that have nothing to do with faulty electronics. Get your scan tool out and start looking, a true data logger would be much better so you can go back and review the data without necessarily having to watch it in real time.

Look at things like the IAC position when it's cold. If it's completely closed, or nearly completely closed yet the car still idles, that's a dead ringer that you've got a vacuum leak. If that is OK, then maybe the problem is between the MAF and the throttle body. Those intake ducts can pop off, and we know what happens to 18 year old plastic and rubber. Maybe you've just got a crack down in one of the pleats on the bottom so you can't even really see it but it's still there. There are so many places you could have a vacuum leak that I'd spend a while tracing all of those possibilities before I spent a dime on it.

It may NOT be an air leak and could be some faulty sensor causing it to run rich when it hits closed loop. This will show up on a scanner as well. The 94 is OBDI and therefore really not all that difficult to deal with. I would highly suggest that you buy a laptop, and buy TTS DataMaster and take a look for yourself. You can see exactly what the car is doing and it has the capability to log for hours if necessary so you can go for a drive then come home and take a look at the results from the comfort of your sofa. Best money I ever spent on my car.

 

not chasing it, i can see exactly where its leaking from, just havent had time to do anything about it.

well i already have a laptop, how expensive is this tts datamaster thing..

1. so, your saying that when the car is first started and its warming up, it ignores everything but the computer? that seems stupid.

2. not sure i understand what you are saying here. i thought that in closed loop, it uses the 02 sensors and the computer decides the fuel off of that.

the tb gasket is new, i replaced that because the old one basically wasnt there any more. and i have taken off the maf to clean it and put it back 100% good, so no problems there, i can assure you of that.

last week i removed and or looked at all the vacuum lines i could physically see or touch and it was all fine. looked like most of it was newish. none of it was brittle or hard, none of the fittings were torn, still, i would need a gauge to tell me for sure if there was a vac leak.
if i did a resistance check on the IAC valve, would that tell me anything?

 

When you first start the car it is running in what is called "open loop" mode. This simply means that the computer is controlling the car running off of programmed values. It knows that when everything is working properly it needs X amount of fuel for X amount of manifold pressure, etc. It does use SOME sensors but it doesn't use them all. The reasoning is simple, it CAN'T. Oxygen sensors measure the air / fuel ratio of your exhaust, but they only work when they are hot.

Consider this, your car has been sitting for a week. You go to start it up, what is it going to look at? Can it possibly get any good data from the oxygen sensors? Of course not. First there is no exhaust to measure, the car hasn't been running. Secondly the sensor is stone cold. Therefore it has to look at air intake temperature, manifold pressure, coolant temperature, etc, and make a guess. It does this based on a table of known conditions. Only once the car warms up and all of the sensors are in their operating range can it start using them.

Example... people say that cars that use MAF over Speed Density systems don't need as much tuning, that the MAF can "tune itself." That's true to an extent, because the MAF can read the actual amount of air going into the engine it can add the appropriate amount of fuel, BUT the MAF has to be working. Many a person has installed say a new camshaft into a MAF car and had a car that was a complete basketcase when cold yet when it reaches closed loop it suddenly "fixes" itself. This is because the car has been running off of programmed values that are incorrect in open loop, but when it goes closed loop and starts looking at the sensors it knows something is wrong and can correct it.

Speed density cars don't have a MAF. Everything they know is based off of a table. Based on known information from sensors they take their best guess and then use the feedback from the O2 sensors to tweak it from there. MAF systems do the same thing, they just have the ability to make a slightly more educated guess. Being said a faulty oxygen sensor will cause a problem. Consider an O2 sensor that always reads lean. The car ignores this until it is warm enough then it starts reading from the sensor. It sees lean so it adds more fuel. The sensor doesn't change so it continues to add more fuel, runs like crap, etc, etc. If everything is working like it is supposed to the ECM will realize that the O2 sensor is just flatlined and not responding and it will actually default back to open loop and ignore the sensor.

Your car is obviously running fine in open loop and lousy in closed loop. This could be a faulty sensor or it could be some condition (such as a vacuum or exhaust leak, etc, etc) that is causing a sensor to provide faulty data. And this is why you have to scan it and data log it. It will show you if the car is in closed loop or open loop and it will show you the output from all of the sensors. From there it should be pretty easy to track down.

There are many data logging systems and pieces of software out there. I have always used datamaster, but others will do the job. http://www.ttspowersystems.com/index.html Spend money up front on the equipment and you'll save it in the long run.

 

I would check the coolant temp sensor that the ecm reads.

 

It certainly won't hurt to check, but if the coolant temperature sensor is not reading properly, IE reading too low, the car will never attempt to go into closed loop mode. If this is happening at a consistent temperature it is very likely that the coolant temp sensor is actually just fine and it's something else causing the problem once it tries to go closed loop.

 

Ok, first off Nathan.

While some of what you said is true, some of it is NOT.

The MAF IS an input at ALL times, not just during closed loop.

FYI, MAP systems do not "guess" they take all inputs, put them into a algorithm and set fuel trim accordingly. Once in closed loop, yes the tweak the air/fuel ratio.

The only real difference between open and closed loop is O2 inputs. In closed 02s fine tune the fuel trims. In open it is ECM controlled based on sensor inputs and built in calibration data.

2nd: His car is running better in CLOSED LOOP not open. If you read the prior posts he did noticed that car sputters before 140 coolant temp, once it hit 140 and in CLOSED LOOP it stopped as he noted.

3rd: His car is running rich as evidence by his black tips, this maybe happening during closed loop or open.

He has verified fuel pressure being ok.
Until we get a good scan tool on it to look at the inputs from the sensors, NO one will know, what the heck is going on. Until then we are all guessing.

Irish, yes your ECM is easily tunable, but if the car is stock and the tune is stock. I'd get the car working correctly first, then worry about the tune. Changing your tune now might band aid the real issue and could potentially cause more issues.