MysticDreamer

Hi all

I have come to this forum often and let me say, you all have helped. But I need more help from other Vette owners and enthusiast.

I recently purchased an 85 C4 350. Thinking L98. Not sure. Before I go further, let me tell you I am engine stupid. What I know is what we have done, and that's about it.

When we bought it, it ran hard. Jumping, idled all wrong, sounded like crud. So we bought it to fix it up. We started with the full tune up: oil change, filter change, radiator flush, new wires and plugs, new cap and rotor as well as water pump for good measure.

That seemed to mellow the car out, as it did have the wrong distributor cap. I have put more than 4000 miles on it in 4 months. As time went by, new problems emerged. As we fixed one, another was created.

Let me keep it short, and tell you that as of now, the car idles hard, Dies sometimes. Hard to crank. CHUGGS! at certain speeds or certain shifts it starts chugging. Sometimes so hard it hurts. Other times the car cranks fine, runs fine, and the tires will cut loose and leave rubber.

Now let me tell you what we have done. Some in other fixes, and the rest with this problem.

Replaced ECU, upgraded spark plugs and wires (ac delco) MAP, MAF, IAC valve , o2 sensor and knock sensor. Entire fuel system, rail, injectors, pump, filter, wires to pump, cold start, timing chain and cover, throttle position sensor, throttle body. Took off exhaust at motor to make sure is clear of debris and no issue with catalytic converter. Took out air system, removed the radiator and cleaned out debris around that area. Checked and replaced vacuum lines. Checked compression (160-165) checked psi on fuel (39 psi all 8 pulsate hard) Deleted EGR valve. No difference with that.

I am sure we have done more, it seems so much in so little time. This problem started as we fixed another problem. The car started chugging and rattling. It sounded like a weak powerstroke. So we flushed the fuel system, went to premium fuel, changed the entire fuel system. Now the chugging is still there, but it feels like the car wants to go but something is choking it. I can feel the engine respond but it doesn't go further than that. At idle it seems to lope, but not a natural lope. As I am not mechanically inclined, I am frustrated and about to drive the car to a cave!

Any suggestions would be awesome! And thanks in advance!

87 vette 81 big girl

Very possible a fuel injector is failing or has failed.
Plugged up injector.
What that really means is that the inlet side of the injector has a tiny pressed in very fine mesh strainer screen.
Plugs up very gradual from dirty gasoline.
27 years worth of unknown gasoline quality has gone through since 1985.

Your 1985 Corvette has the BOSCH type 1 fuel injectors.
They each are rated at 24lbs per hour wet fuel flow.

Rebuilt injectors or having your Original 1985 Corvette Fuel injectors are some possible options for You.

BR

MysticDreamer

I did have 5 bad injectors. So we replace all 8 of them. That cleared up the clanking like a powerstroke.

87 vette 81 big girl

Any stored codes ever or recent in the ECM- computer ?

1985 Corvettes had a special 1985 spec BOSCH hot wire MAF sensor & unique under dash mounted electronic MAF burnoff module.

Others will chime in later today for help.

I am more familiar with the 1987 & later C4's.
1985's are similar but unique yet from any other C4 model year.
1st year of the L98 Tuned Port engine.

I own a 87 Convertible.
Fixed many bugs & headache problems myself on it in last few years owning & driving it.

87 vette 81 big girl

There was a bad run of HEI ignition coils mounted on top of the distributor cap for the 1985 & 1986 Corvette model years.

I recall seeing the GM service bulletin on it back in 2007 when I last worked in GM dealership turning wrenches.

Possible you have the original Ignition coil in place yet & it is failing internal.
Be a hard problem for the average home mechanic to diagnose.

Easy to replace the ignition coil though if defective.

Brian

MysticDreamer

We have not pulled codes yet. My husband is a professional diesel mechanic, and we are waiting for the connector to our genisis to come in. We may just take it in to Auto Zone. I am familiar with the Bosch unit and my husband said that is good.

Brian, that is good info to know, I will pass that bit on. I remember hearing talk about a coil on the distributor, but they were not too worried about that just yet. But we just replaced the ECU today so we might revisit that.

I am just tired up dumping money into parts that were not broke to begin with.

87 vette 81 big girl

Its not 100 % required to use a scanner on old C4 generation Corvettes to pull up stored trouble codes.

A simple bare wire steel paperclip is all you need.
Unwind the paper clip,
form it into a " letter U" fashion.
Jump pins #A & #B with the paperclip.
Watch the Yellow Idiot service engine soon light start flashing.

1 flash followed by 2 rapid flashes equals code 12.
Code 12 means the system is OK when checked in self diagnostic mode.

Any other codes will flash in similar manner.

Codes flash 3 times in a row before moving on to the next stored code.

I dont recall all the different codes & what they exactly stand for.

A factory GM service manual or an aftermarket HAYNES will list the codes next to the 2 digit code numbers.

Have something more to work & troubleshoot with then.

Past my bedtime.

Goodnight.


Brian

oldalaskaman

its impossible to put the wrong distributer cap on the early c4's, theres only one. I suggest you quit throwing parts at it and take it to a shop. it seems to be running pretty much the same as when you bought it so you obviously have'nt thrown the right part at it ...yet. since your husband is the mechanic, you should have him post on here, that way info doesnt get lost in the translationBTW, the money you've spent on parts probly could've got you a good running one

MysticDreamer

Thanks Brian, again good info to know. And I will tackle that soon. I do have a list of the trouble codes.


I beg to differ. When I went to buy my cap, Auto Zone had 4 of them. And all 4 were different. The one that was on it, was bigger than the one I have now. I purchased that myself. I appreciate your opinions, but obviously you did not read that the car had other issues, as to why it got other parts. Now, I am at the standstill. Nothing is getting lost in translation. Like I said in my OP, I am car stupid, but I know what we have done because I have been part of 95% of it. Thanks, but no Thanks.

And as for the money, I never complained about money. I Like THIS car, and so does my husband. If not us, someone else or it would have went to a junk yard. We have had fun repairing it up until this point.

oldalaskaman

lady , I've been a mechanic for over 40 years, there is only one dist. cap for the early C4's, nothing else will fit, yours being one of them, good luck

MysticDreamer

I appreciate your thoughts. But I know what cap we took off, and what cap we put on. When it got changed it ran a whole lot smoother.

navy_vette

This is TPI. It's the intake present on the L98. If you have this, it's an L98.


These cars are a very picky.

You really have to concentrate on 3 broad strokes.

Fuel:
You replaced the injectors. That is one of the more common problems. If they were plugged, your fuel filter might be too. They are easy to find a relatively cheap. You also might want to check your fuel pressure. You can get a fuel gauge at Autozone for cheap. This is a really good article on fuel pressure.
*I know that you already check fuel pressure. However, you should also make sure that you don't have leakdown. After it hits 40 PSI, turn the car off and leave it sit for about an hour. You shouldn't see it drop too quickly. It shouldn't be much less than 40 after an hour.

Spark:

New distributor is a good start. If it is brand new, you really don't have to worry about burns or arcing. If you got it from a junk yard, you might want to take it apart and check every single metal piece on and inside it to make sure they are clean. Plugs and wires are new, so they shouldn't be a problem. Using dielectric grease on the connections between the distributor, cables and spark plugs can help. There is also gaping on the plugs to deal with.
Also, check the wires connecting to the distributor as far down as you can. I found out that one of the 12V wires to the distributor was spliced THREE TIMES. Splices cause voltage drop. Voltage drop = cold spark.

Timing:

New distributor, again, is a good start. However, timing is always a problem when dealing with these motors. After I got my motor back from the first mechanic (I'm not going to name names, but they sucked) It started running rough about 2 weeks later. I found out later that they did not tighten down the retainer fork enough. So, every time I cranked the motor or stepped on the gas, the distributor would jump and the timing would go a little more retarded. Eventually, I couldn't start it. Re-timed the motor by ear and it ran great.

The exhaust can tell you a lot. If you have a lot of "smoke" that smells like gas in the beginning but not after a minute or so, you could have fuel leak down. If it smells sweet, then it's coolant. If it's oil... You'll know if it's oil.

And last but not least...
WELCOME TO THE FORUM!!!

After busting you busting your knuckles around this car for awhile, your knowledge will increase. Go make your husband's friends jealous of your never ending knowledge of your new favorite car!

Have fun and take your time. Even rushing a throttle body cleaning can turn bad

MysticDreamer

Thanks tons, I can't stop to read your post, I am on my way out. But that is my engine. And so I have heard about it being picky! Thanks again, I will let you know more tomorrow when I have more time!

1963SS

Welcome to the forum and enjoy your Corvette. We ALL love them. When you do the paper clip trick to retrieve your codes let us know what they might be. A lot of guys one here (myself included) have some experience with what usually causes a particular problem. Looking forward to helping with this and have a great day.

It's always enlightening to have new members that want a properly running Vette. You do realize that pictures are mandatory for all new members. All we do is sit at our computers and wait on pics. Not to be sexist or anything but new lady Vette drivers have got to post pics of themselves. Just kidding, of course, but..........!

Midnight 85

Your first mistake is buying parts at Auto Zone, your second mistake is ignoring oldalaskaman's advice, there IS ONLY ONE distributor cap for a 1985 Corvette! There may be different caps price/quality wise but they are all made the same as far as fit goes.
You've stuck a boatload of money in the car without checking the codes???

nickpe

nnnn

Pwnage1337

Perhaps the idiots at autozone told her that there are 4 different caps. Who knows, they may have the wrong part numbers applied to the search application when they search for 1985 corvette. It wouldn't be the first time it has happened.

Whenever i go to parts stores, i always take the old part with and open the box right on the counter so i can compare them and make sure they are the same one.

87 vette 81 big girl

Don't give up.
Something all of us C4 owners & drivers have in common.

I can not over state how important it is to have a bright hot blue ignition spark present at all times on an EFI equipped car.

A weak yellow or orange ignition spark causes engine misfires & strange driveabilty problems I have seen hundreds of times.

Most modern day mechanics over look the basics.
But the basics are still in place as always.

navy_vette

"This one is a "universal" distributor. I put it on my 81 honda and it worked great!"

Part numbers help. Using the forum's sponsors help a lot. You KNOW that you are getting the right part. Most of them deal with Corvettes specifically. There is only one style distributor that is CORRECT for this car. Make sure they know that it is for a TPI Corvette. They might have been trying to give you a standard Chevy SB distributor. NOT THE SAME.

Trust me, stick with the sponsored links.

oldalaskaman

not to flog a dead horse, but since early in the 70's, when chevy first started using that distributer, and I actually remember when we first saw them, there has only been two versions, the first has 'L' hooks to retain it to the distributer, the 2nd which we early C4 owners have is exactly the same thing only has screws to retain it to the distributer. hope this helps