junkyard_dog72

This will be a long post separate from my project thread because its an off string of issues.

To start, it has a miss when you give it gas upon start up. After a 5 minute or so warm up period, it runs right. Or it ran right until the next set of issues. That problem still exists.

The problem originated about 2 weeks ago when I took the car on a trip from Cincinnati to Indianapolis and back for the speedway cars and coffee. On the way there, it averaged about 85 MPH at 25-2600RPM. It ran like a dream. On the way back from the track, I hit traffic for about 20 minutes starting and stopping, then began driving at similar speeds on the way back. At around Rushville, IN the car got loud like an exhaust leak. I stopped for gas at the next exit at Love's Truck Stop. It still seemed to drive fine until I got off the highway in Cincinnati, where it was still incredibly loud and began running like garbage for the 4 or so miles home off the exit. It had a miss, backfire, and did not want to move. Upon arriving home, I thought it had bad gas because the injectors were screaming loud. It then proceeded to get quiet as I let it idle to burn what I thought was bad gas. Fallowing this, the car would not start because the starter went out. After replacing this it started.

Later that week, I drove it 25 minutes on the highway to work, where it began to get loud sounding like an exhaust leak and loud injectors. I once again let it keep idling, where it got quiet and ran smooth. On the way home, it got loud once again and made the same struggle as above off the exit. i stopped at the Meijer off the exit, where my dad met me to see what the issues were. He then drove it home where it ran loud, but had no miss in it.

We thought it was catalytic converter related, so we gutted what was remaining in the catalytic converter and adjusted the TPS.

My dad drove it earlier this week on a 20ish mile drive with no issues. Today, I drove it 5 miles, then came back in an hour, drove it home another 5 miles where it began having the same poor running and exhaust leak sounding issues.

Short Summary: Upon first driving it, it runs great. It is smooth and as quiet as a Corvette could be. After some driving, it gets loud then follows by running rough with a miss and exhaust leak type sounds.Oil pressure stays consistent at 80, water temps and oil temps are all normal.

VikingTrad3r

my first gut is distributor related.

that said, you will want to do the usual stuff:

1. borrow a fuel pressure tester and stick it on the windshield taped towards you and go make the car create the issue. eradicate fuel pressure as an issue.

2. pull the cap to inspect it. just make sure everything looks allright under the cap. i say this because i had similar symptoms and my strap on the top of the rotor was gone and the arcing from the bottom of the coil to the point actually ran the car but got real bad at rpms. not the same as your symptoms but worth looking at cause its easy.

3. idle it in the dark and spray a mist of water over the plugs and wires to see if the light show starts for you. could be as simple as spark plug arching.

4. any codes?

thats as far as i can think right now.

junkyard_dog72

Thanks for the quick reply! I'll start with the fuel gauge on the windshield. None of the noises are knocking or ticking noises, but it's definitely not right. Once again, thanks!

junkyard_dog72

https://www.corvetteforum.com/forums...e-project.html

Here is a link to the original build threat. Last night I tried starting it with the same poor running issues

mickey5

How about a blown head gasket? Missing and noise after it heats up...maybe.

junkyard_dog72

I'll check on the oil to see if it is milky when I get back to the car for the day. I had checked it previously and it appeared to be normal. I appreciate the suggestion

mickey5

Nothing would show in oil or coolant if the gasket breached to the outside and would make a steady pulsating noise.

junkyard_dog72

I used a SNAPON Solus Pro and scanned the car quickly last night. It showed a code 33 MAF and the TPS was reading too low at .44. More will be done tonight

VikingTrad3r

Hey Junkyard,

When you used that scanner on your 85, did it force the car up to 1000rpm ?

that is what happens when i use tunerpro rt and an aldl cable.

junkyard_dog72

Don't go with this 100% but I believe it did for a second or two, then dropped to normal idle. How do you go about scanning with your car? Is it a computer program you are using or is tuner pro a scanning device?

VikingTrad3r

using tuner pro rt with aldl cable.

i have NEVER found a way to scan an 85 without the ecm being forced into field test mode which forces the car into a 1000rpm idle among other things.

if you have a chance to double check it id sure love to know if tou are able to observe normal operating behaviour of the 85 with that scanner.

gerardvg

Hi
I also use tuner pro and noticed the 1,000 rpm when connected,
I have found some scanners do not have that effect.
They were just plain hand held commercial ones that plug into the ALDL ..

junkyard_dog72

Today when setting the idle I had to unplug the scanner due to it idling at 1000RPM.


After working on code 33, the issue still remains. On a test drive the car ran fine on regular roads. Then randomly, there is noise from the engine that sounds almost like a tapping while under load. Engine runs normal until warm and accelerating under load (accelerating to merge on expressway) and remains. There is a decrease in power as well as popping under acceleration once the noise starts.

All noise comes from the top of the engine mar injectors but does not sound like a knock or tick. I have data from cold start and beginning of warmup from the scannner, then from when the issues immediately began. I'm working on putting those in a spreadsheet for comparison. This one is baffling for sure. Car has 125,000 on it.

VikingTrad3r

gerard if you recall or can dig up which scanner it was (old but maybe still avail on ebay??) i would really like to know. its the 1 issue sith 85's. would awesome for the community to know!

sounds like its closed loop issues only???

gerardvg

Hi

It was around 6 or 8 years ago before i started using tunerpro, i cannot recall what the scanner brand was. They went out of business, i remember he set the idle via IAC counts you can only do that at normal idle. I cannot do that with Tuner Pro

gerardvg

Hi

I have photographed and attached the 85 shop manual code 33 diagnostic pages below, once you have a look and do some tests you should be able to diagnose the problem.

It sounds to me that the popping noise you are hearing when warm is from backfire, i have come across this in the past thinking it was a MAF issue. Actually was a knock senor issue retarding the timing way to much, with an already retarded distributor due to the blower.

You need to find a friend who has an 85 corvette, then you can swap the MAF or burn of module as a quick test.
Pity i am in OZ, i have a spare MAF Burn off module ...ECM.. Distributor.. EST module you name it, when you live on the other side of the world you have no option but to pay Premium local prices or international shipping ..
You cannot find a bargain when you need a part fast....

The 85 MAF is a one year only, the 88 MAF is the only other one that works on the 85.
I got a replacement MAF from Ecklers, make sure the MAF is a hot wire type.
There are some that have no burn off wire, they look different inside so check carefully.
I got one of those weird ones from corvette central, it did not work and they could not care less.
That is the last time i will use them, it was for 85-89 it said on the box....

Make sure the CAT is not blocked, rev the engine and see if the exhaust flow is the same at each muffler outlet.
A blocked cat or muffler can choke the engine..

The 85 only burn of module used to be dirt cheap, i got a spare before word got out that they are quite rare...
Below is a link to one on ebay...

http://www.ebay.com/itm/1985-Corvett...dYH21M&vxp=mtr

Silver85

I think the issue is in the EPROM and not the scanner itself. Part of the .bin file has a timing bump when a scanner is connected. When Greg with Blower Works programmed mine he took that out.

junkyard_dog72

Prior to below we did the MAF and TPI reset.
Here is the data pulled from the past two days, each chart has the description on the top right of when it was taken:

junkyard_dog72

I started the car up again today and after some closer listening it sounded like a Loud clicking noise as compared to a tick or a knock. Oil looked okay, so no change there. I'm not sure if this is an extension of the car's miss on startup throttle like before or if it is completely unrelated.

Edit: thanks to all who have read this and tried to help out, I appreciate it. It hurts not driving the Vette on nice days!

Dt86

Your block learn is maxed out at 160. The ECM is seeing a lean condition and adding fuel. You have unmetered air getting sucked into your engine from somewhere. Check your exhaust manifold bolts to see if they are tight.