Working on her now

 

Ok,
Timing set to 6° BTDC. Disconnected the EST to set the timing. Then reconnected the EST and turned off the engine and disconnected the battery for a few minutes. Then when I started the car the timing did advance beyond 12°, as it is supposed to. Funny thing I noticed, reving the from the throttle body work perfectly, but when I got in the car and hit the gas pedal the rpm would drop off around 3900. My guess is TPS. Thoughts?

 

But the TPS will read the same whether you operate the butterflies by hand or use the accelerator pedal. So maybe check with the engine off that the pedal opens the butterflies all the way. Maybe the cable is just out of adjustment.

 

Thanks, I will verify that tomorrow.

 

Unfortunately I took one step back after two forward. I attempted to check the voltage in the TPS and adjust it to the correct voltage. My multimeter was not giving me a clear reading. I thought I was at 55 volts, but now when I start the car it won't stay running without me hitting the gas. I used a video on line for guidance. There is a step by step guide here on the forum. I will try that tomorrow. Kinda bummed but learning ad I go.

 

Yeah you need a decent multimeter. Iirc it should be about 0.54v at closed throttle and something over about 4.5v at WOT measured with key on but engine off. There are two set screws to adjust it (I think). I you can’t adjust it properly no mater what you do it will be stuffed.

 

I will go back through the TPS install process and then reassess the voltage. I am confident to figure it out, however it will take a few shots in the dark. I am also going to see if I can find out why my dash has no power. More to follow. Thanks again for the feedback!

 

Something to think about with fuel is the Fuel Pressure Regulator. If the FPR is leaking it will run shitty or not run at all. Pull the vacuum line of ithe FPR and check for fuel in the line ... if so it's leaking.



BAD FPR


I've replaced mine being bad 2 times and I have an 1986.

 

Hello MarkB85Vette!

Have you had any issues with your MAF sensor? The MAF measures the air going into the combustion chamber and when they start to act up they send some really wacky data to the ECM and that could be part of the problem. You will need to use a scanner or something like this to see it in real life. They can be cleaned with great care and the "proper" spray chemicals. The wires in the MAF are like 1/10th of a mm wide so don't use anything that might break one of them.

But the other thing is the ignition system and the health of it. How old are the Plugs, Distributor cap and Rotor and spark plug wires? I have seen plenty of cars run a whole lot better after replacing the consumable parts.

We have seen knock sensors that have failed and they cause the timing to pull back 10* at the start and slowly return the timing unless another knock was heard. There was a Corvette hearing knocking at 4000 rpm recently and it lost power as well due to the computer retarding the timing. A failed knock sensor can send a signal when in fact the engine is not actually knocking or detonating. This very thing happened to my C4 and the car would not outrun a toyota. I put a new knock sensor and I am spinning the rear tires again... It is possible to test a knock sensor, you monitor the output signal and then hit the engine with a ratchet or something metallic to trigger the sensor. I suspect that yours is probably responding to something and retarding your ignition for you. Just a thought...

Be aware though if your knock sensor is bad you will have to install a new sensor. The problem is the knock sensor is at the bottom of the cooling system in the engine block so when it comes out of the block your coolant will flow out as well. The best thing to do is to plan a coolant change when you change a knock sensor. Again, if you had a real time monitor you would see these things on paper or a screen.

I don't think an engine that only revs to 3900 rpm is being caused by the TPS. Or the IAC.

How old is the Oxygen sensor? If it is over 24 months old or 50k miles of use then replace it. The signals get weaker (Narrower) over time and they start to lag which makes it harder for the engine to keep the proper air/fuel ratio since the O2 is not reacting fast enough. Contrary to Popular Opinion the Oxygen sensors have a specific lifespan, they can continue to work but not as accurately as a new one will. A new sensor will help regain the performance and economy we enjoy with our Corvettes. Since we only have one it won't break the bank to buy a new one. Newer vehicles have as many as four O2's on them.

Last thought, How about your catalytic converter? If they get plugged up the engine will start and idle fine, once you step on the gasoline they just sputter and cough. Remove your O2 sensor and see if you have pressure blowing out the hole while the engine is running. Even a partially blocked catalytic can keep the engine from revving normally.

Hello GregMartin,
You have lots of good ideas and I see you helping others regularly. I commend you Sir! You Sir, are a "True Gentleman" trying to help those on the Topsides of this world of ours. I have never been to Australia but I have heard how beautiful it is from family that went there. I have been in over 44 countries so far but not down under. I was invited to the Prime Minister of New Guinea's home for a Bar-B-Que as I entertained him and some of his associates on a trip to Mexico one time to see our Hybrid Solar Power Systems that we used to build for villages with no power. Taking a group of Aborigines on a tour of Mexico and meeting with the Mexican President and Senators was a "True" experience of a lifetime. We did a system on Coconut Island off the coast of Australia.
In my earlier years I was a glutton for punishment and bought a BSA 441 Victor as a basket case (Literally). I spent a lot of time acquiring "Went worth" tool's to fit the BSA. It was an experience building a Running 441 without a shop manual...
Then several years later I was ridding a motorcycle while a buddy was on a BSA 650 twin and we were zooming down country roads in the dark when LUCAS "The Prince of Darkness" took over the BSA and shut off the headlight in the midst of a tight turn. It took us a while to get that bike back to the highway... It took longer for my buddy to heal his broken arm!

May you all "Be Well and Stay Well"

 

Hello to all,
Greg, my ignition is all new. New plugs, wires, distributor rebuilt. The TPS is now perfectly at .55v and goes up to 4.3v at full throttle.

As for all.of the other suggestions, any could be a problem. I looked in my Chilton manual and it did not show a knock sensor on the vin 8 engine. But that may be an issue. As for O2, Cat, and all of the other suggestion, none of this possible problems have been ruled out. But the TPS is good, the car drives fine if you accelerate slowly. Once you hit the gas is drops out. So the first question, does the 1985 L98 have a knock sensor?

 

Good morning Chris
You’ve given Mark many good suggestions here. I think the next step is helping him to get a scanner hooked up. Being an old control systems guy I want to know what the ECM is thinking.

Also thanks for your kind words. There are quite a few people on this forum like yourself that have plenty of experience and are willing to help. I kind of live by the moto if you can help you should and this forum gives me that opportunity. I certainly don’t know everything but I’ve had lots of cars over the years, been involved in motor sport, and worked in control systems, that all helps when diagnosing faults on these early computer controlled cars.

If you get the chance to come to Australia I’m sure you would enjoy it and my door is always open. It is a long journey particularly from the eastern states. I’ve been to the US three times, the west coast with work, the west coast with the family (take the kids to Disney Land etc), and NY with the wife. Apart from the 16 hour flight I’d like to spend more time in the United States, in general the people are warm and welcoming and the country is beautiful.

Oh and I’ve have a few British cars over the years so I’m quite familiar with “Lucas prince of darkness”, also prince of failing in the wet, which always surprised me considering the amount of rain in England.

 

You guys should come to south Texas, Corpus Christi has some of the best beaches and fishing in the world. Thanks for all the advice. Seems to me, since I do not have a scanner, need to get one, the knock sensor seems like a good choice along with the O2 sensor. If I accelerate slowly the car runs great. But won't respond when you punch it. I hope all.of you and your families are well.

 

Hi Mark
All of Chris’s suggestions could be the problem or it could be fuel pressure caused by an number or things including the regulator. It really is just a process of working through the list of most likely to least likely.
The quickest way to work out what’s going on is to interrogate the ECM and probably measure the fuel pressure because I don’t think the ECM has a fuel pressure input.
So the fuel pressure is easy there is a Schrader valve on your fuel rail. Hook up a pressure gauge and see what it’s doing. When you rev the engine it shouldn’t move. The real test is to tape the gauge to your windshield and go for a drive. If the fuel pressure drop when engine load is applied them we found the cause of your problem. If not we need to hook up a scanner and see what’s going on. On these old cars WinALDL is popular have a look at this link to get it and see how it works.
http://winaldl.joby.se/
It sometimes takes a bit of effort to get it going but I can help you with that and once you do you will thank me.
Oh and one more thing you do definitely have a knock sensor. It is at the base of the block on the RHS. If your coolant system doesn’t leak then you should be able to remove and replace the sensor without much coolant running out because of the vacuum. Also there is a torque setting for the knock sensor, if you do it up too tight it become too sensitive. I thick the torque setting is about 14 foot pounds but I’m not 100% sure.

 

Before this Bat Beer virus I could get a direct Qantas flight to Houston so it was on the list to visit your neck of the woods.

 

Nice! And thanks for the program download. I will use this to figure out my car, as well as verify fuel preasure

 

You will need to make or buy a cable. I bought one that didn’t work then I made one from the directions on the website and it worked fine provided I put the 10k resistor Between pins A and B.
All the cable does is invert the RS232 signal.
In the mean time you could short out pins A and B on your ALDL connector and check for codes. It works like this you short out A and B and turn the key on. The check engine light will flash once then twice then a longer pause. It will do that three times. That is code 12 ie once = 1 and twice = 2. So it flashes code 12 three time. Code 12 means that you are in interrogation mode it will then flash each error code the engine has three times. For example if you had a code 44 the check engine light would flash 12 three time as I described above, then I would flash four times pause briefly and flash four time again. It would do that three times and then flash 12 three time again indicating that there are no more codes. It can sound confusing but it will be obvious when you do it. If you had two code up say 43 and 44 this is what you would see:
12 12 12 43 43 43 44 44 44 12 12 12
For a list of codes look on the internet or in your FSM when you get one.

 

I have not chased the wires yet to get power to my dash. That is one of the next things I plan to address.

 

Oh so you mean nothing on the dashboard has power? I thought you just meant the LCD, tachometer, speedo, etc. The Check Engine light is on that panel in the center of the dash next to the switch panel and above the radio. That’s also where the seatbelt warning light and handbrake lights are located.

 

Ya, I know where all of those are, the guy I bought the car from installed a new instrument cluster that works just fine. I am guessing when he installed that he disconnected power to the rest of the dash. There are no indicator lights, radio, and such working. The heat and ac come on but dont blow very well. I have to see where it is unplugged. All of the fuses are good to go. When I get the dash power on, I can start checking codes.

 

Yeah OK
i think the biggest problem with these cars is all the d$@kheads that have bastardized them in the past. I think there is an Auto Meter dash that was made as a replacement for the LCD panel. I imagine if that’s what was used the wiring should be mostly intact.
Anyway good luck with that.
Edit: I guess it’s something like this
https://www.ecklerscorvette.com/corv...1984-1989.html