Bangkok Dean

I have been having problems with the motor not running or stalling for 3 years now. I now can get it started after I found a broken vacuum hose going MAP sensor. But it would still stall dead and restart easily. So I replaced the ignition module and pickup coil in the dizzy. So now it runs good at highway speeds but still stalls after sometime at slow speeds.

I hear a lot of air noise similar to when the motor is cold. Also in overdrive at slower speeds it sound like there is detonation.

As you can see in my other link I don't have a way to check codes.

Any ideas?

https://www.corvetteforum.com/forums...wo-a-dash.html

TheBlaster9001

Have you set timing? TPS/IAC calibrated? Will a code reader not work on your ALDL setup?

Sounds to me like you have a vacuum leak still. The air noise you mention makes me think so, unless you mean a different air noise? Try and find where the noise comes from, there's a few tricks out there for finding leaks, usually you can get close by ear though.

If you hadn't mentioned the air noise, I would suspect the IAT sensor is not working right.

Bangkok Dean

The air noise is from the IAC, In the past that sucking noise was only when cold starts and went away when warmed up.

The timing was set at 6 degrees, following the instructions on how to set timing. The pinging is only when in 4th OD gear if I shift to drive bring the rpms up the pinging goes away.

I don't have a code light in dash so no way to get codes. Working on that now.

aklim

When my IAC opens up, there is a huge sucking noise. Maybe it is that? Only way to know what is going on is to scan it for data and forget the codes.

aklim

Maybe you hear it more when the IAC opens up more? I don't hear much over the engine noise till I get past 80 counts.

How do you know there is pinging and not something else? Have you scanned it to see?

Forget the codes. Get a scanner. Codes MAY only point you in the right direction. With a scanner, some people with may be able to tell you what the data says is going on. People place too much faith on the codes. It is a crude system that doesn't do much.

Bangkok Dean

As no one in this country has a scanner, so it is only guess work.Thanks

For 3 years I have been struggling with the stalling problem.

Still considering scrapping the TPI and getting a good old dependable carburetor. It would sure save me money and aggravation.

Over here no one used a GM V8 only a Toyota V8 and I know why.

aklim

Why can't it be you? https://play.google.com/store/apps/d....scan&hl=en_US

All you need is an android phone and a scan cable. IT will come in VERY handy when you have an issue so you don't throw parts til it works. Look at what I just bought to replace my broken one. https://www.ebay.com/itm/AutoXray-EZ...72.m2749.l2649

TheBlaster9001

Huh, I haven't heard an air sound on mine before. Since timing is set right, and assuming engine is stock, pinging is likely the result of too little fuel, or low octane gas. How old is the gas? It might need to be replaced. My girlfriend's 86 had a year-old tank, and it rattled like a snake it knocked so bad. Shut it off quick, siphoned, and refilled, and it fixed the pinging.

Now, too little fuel could be the result of bad sensors - which would also explain the poor running. For MAP cars, like yours, the fueling is largely determined by the MAP sensor (which seems to be working since it didn't start without it connected), IAT sensor (which I suspect may be faulty in your engine), and TPS.

So check that the TPS is calibrated correctly, and if/once you get a way to read codes, replace the IAT if it has a code. At least that's where I would start.

aklim

Pull of the hose going to the TB from the air filter and listen carefully when the engine is trying to raise the RPM or force it to raise the RPM by turning on the AC or covering part of the butterflies.

If there is insufficient fuel, I would check the fuel system first for pressure. Can't check volume unless he does a WOT run with the gauge taped on the glass to check for delivery under load.

I would scan the thing and someone can do the same here with an identical engine under similar conditions so he has a baseline to see if the MAP is correct. I'd do it but my system is far away from his so my baseline is incorrect. If it is the IAT, again, he needs to see if it is reporting right by hitting it with an IR thermometer and scanning to see if the ECM agrees.

IIRC, there is no way to do adjustment on the TPS for his car which is SD. Mine cannot. It accepts the initial value at start as baseline voltage even if it is not at 0.54V. So whatever voltage at startup is 0% throttle. I'd forget the codes and have him get a scanner to see data. The codes are at best vague and at worst, misleading, IMO.

TheBlaster9001

Ah, that makes sense, I didn't realize that MAP cars didn't need adjustment with the stock ECM. I agree codes can often be misleading, but they cost you nothing and are easy to pull, and when you follow the instructions in the manual for each code, you can sometimes get the answer you need. But having the raw data is more useful, as it can help understand when an issue happens, as well as what else was going on when it happened, as opposed to the codes just telling you what happened.

aklim

The MAF TPS is slotted while the SD cars are just holes.

Bangkok Dean

Fuel pressure is a steady 43 lbs.

To give you some idea what my system looks like.

Bangkok Dean

That scanner is sold. Not sure what scanner I actually need?

aklim

You said it was a 1990 motor SYSTEM so it should have

.

Bangkok Dean

On my plug I only have three wires.Now I wonder what system I actually have?

I do have the DataMaster-8D program on my laptop but have no idea how to read the data after scanning.I could run that again if I could sent the data to someone who can read it.

aklim

Odd configuration Looks more like an ECM other than corvette Maybe F-body?

Bangkok Dean

I bought the setup in 2010 from arizona.

Like I said it runs OK till it gets hot 180 degrees and after some time driving at low speed, the motor just shuts off but starts right up.
It is now fues related or spark.

This has been for 3 years now.

TheBlaster9001

Does it shut off out of nowhere? Or when you hit the gas from a stop?

Bangkok Dean

Mostly applying the brakes, not hard stop but slowing or just lightly tapping the brakes. It dies but putting it in neutral and rolling turn the key off and it starts right up.

BTW, what does the manifold air temp sender do?Can it cause my problems?

TheBlaster9001

Manifold air temp (MAT), also known as intake air temp(IAT), is a primary input sensor in MAP-style engines like yours. Without getting too in-depth, it is responsible for helping the computer determine how much air is actually coming in to the engine - the Manifold air pressure sensor can tell the computer how much pressure the air is at, and with the input from the IAT, it can know the temperature of the incoming air. Using the combined gas law, Pressure * Volume = k (a fixed amount of air, for example, the volume of your intake) * Temperature. So the computer knows the volume of air incoming based on the MAP and IAT sensors. I had mentioned above that I would suspect that the IAT/MAT is bad on your car, as without it, the computer can only guess about the amount of fuel to mix with the air.

Pressing on the brakes killing it would also make me wonder about a vacuum leak in the booster. Do you have vacuum boosted brakes? Any chance they are bad? You can try disconnecting the brake booster line, plugging it, and seeing if the car will die.

Edit: to make my answer to your question more clearly, yes, I do believe that a bad MAT could cause stalling/shutoff. But if the actual use of the brakes is what kills it, it may be a vacuum leak. But should it die regardless of if the brakes are pressed, then the MAT may be at fault.