Hey guys,

I have a 1985 Vette that i've been tinkering with for the past 3 months to try and get it running right.

I've been lurking on the boards trying to diagnose the issues and while the car is running better it is still not running well enough to drive.

Right now the car will start and if idling it will knock REALLY hard....usually it will stall out in less than a minute but it pops are knocks really hard unless you get it above 2000 or so RPMs. It does this while you are in gear or not in gear (it's an automatic)

When I got the car it didn't run and the guys before had tried for months to fix it, but they never could even get it started...it now starts at least...

So far i've replaced...

Fuel Pressure regulator
ECM (whole computer board)
Fuel Pump (the guys before installed some generic one that only got 30 psi)
Rebuilt Distributor
Knock Sensor
Cleaned the injectors
The fuel system wasn't holding pressure at all after the new fuel pump so I replaced pretty much the whole system and now I get good pressure 39psi that holds without issue.

What's got me confused is that even tho it knocks like hell the computer never turns on the Check Engine light.

I've timed it (without the ECM) and set the timing to 0 degrees and when you hook up the ECM the timing swings wildly up to almost 6. I've tried then timing it to 6 degrees without the ECM and then the ECM will time it well off the scale (around 11 or 12 degrees)

I am totally out of ideas at this point....I feel like i'm close but i'm just missing that one thing that i need to check.

Thoughts?

 

Oh almost forgot I replaced all the wires since alot of them were really cruddy looking, and all the spark plugs. And battery...lol

 

When you set the timing to 6 degrees with the wire disconnected, the timing will show around 22 when you connect the wire.

 

That is exactly what I'm seeing...(i'm working on it right now as i post this)

I got it timed directly on 6 and the ecm sent it well over the notch.

So it sounds like my timing is ok? Why is it still popping so hard..? Would it help if i posted a video of it doing it?

 

http://youtu.be/VkIMrmcNj-4

here is what it does..this is a video from today

 

Double check your firing order. Sounds like you might have wires crossed. Check wires (ohm them), check plugs (any insulators cracked??)...did you build the wires or were they precut?

Firing order should be: 1-8-4-3-6-5-7-2. Distributor turns clockwise.

Did prior owner have the valve covers off? Did PO try and adjust the valves? Can you tell if there is a new VC gasket...that might give you a clue if he took the covers off.

 

I don;t see where you bought a FSM ?
You can't diagnose an engine thats 100% computer driven with these specs that are ALL critical and adjustable.

Can;t be done.

How are the harness grounds?


get your FSM first.

Next, after you get that set of books, Go read on the MAF and its relays. Get your TPS set to spec, set the timing with the ecm/dist wire D/C as instructed, and order a set of injectors. I can assure you that IF you got your stock inj clean (which you did'nt) that does nothing to help with the antique nozzels and worn out solenoids and clogged baskets. Replacement sets are $250 from FIC. Gasklets, o-rings and everything.
I guess you Ohms tested the inj hot and cold? Anything below about 12 is outta spec and considered to be junk. 16 is good.

The inj are NOT the reason its burping and backfiring but that will help with getting it to be street ready. The stock inj are trash. They ALL fail. Either thru weak solenoids or trashed internally they were a cheap, poor design that is the very first thing to be replaqced when an engine will not run.

Did you go thru the EGR system and make damn sure that the egr valve is working? hows the solenoid and the vac lines? Other vac lines? leaks?

Theres LOTS to do yet. If you had been doing this with a FSM you;d already be done...

I worked on C4 vettes for 20 yrs before I got my first real FSM. I learned MORE in the following weekend than I did the previous 20 YEARS.

Get the books.

BTW...
The harness grounds and the elec system is so fragile that almost ANY dirty connection or contact will cause it to misfire or backfire.
I spent my weekend taking the harness apart and cleaning and shining all the contacts on or near the battery...to relays, the jumper pole, cables themselves. Age causes things to corrode. Corroded connections change resistence values. The C4 lives by resistence signals that it uses to control everything on the engine. Low voltage reference signals and resistence...probably the 2 most delicate things under the hood and the 2 most overlooked because nobody understands the system. Every control system on the car uses ground path completion thru the ECM to manage the engine. NOT hot wires or "powered" sides of circuits. On a C4 everything is hot all the time...its the ground side that matters. Thats what makes a $100 FSM worth whatever the car would sell for..or more.

 

I just watched/heard the video...

get a new MAF "power relay" (same as burn-off) or get both ($8 ea) and then drive the car while you wait for your new bosch III fuel injectors to arrive.

Its MAF. If you're lucky it's only a relay. $8 vs $250 for good MAFs.

 

Thanks for all the feedback...I'll tinker with it some more today if I can.

I traded a 93' S-10 with 250k+ miles on it for the car...so I expected it to be a bear to put back together. The PO was a 19 year old guy, and when it stopped working him and his buddies just started throwing parts at the car. We honestly don't know what all he did, we have found a few parts that he's replaced with non-compatible parts by using the repair manuals. But i'm sure we've not found them all.

Thanks for all the help tho, i'll take a look at the firing order.

I'm looking at the MAF and I don't see where any part of that is 8 bucks...do you have a link to it?

 

I don't think the PO tried to adjust the values...it looks like all he did was replace the "easy" parts.

I'll check the firing order.

 

Ok I was able to pick up a relay from NAPA on the way home and it is running better, but it still knocks. The old relay was VERY dirty and corroded. So I'm sure that was some cause of it.

I searched that whole car for a burn off relay but I was unable to find it. Are you sure an 85 c4 has one?

i'm guessing now it's the MAF unit itself. We were able to get her to back out and back into the garage under her own power but she soon stalled out. It seems like when the engine is hot it runs worse.

Ideas?

 

The 85 has a mas air module under the instrument panel. it's a one year only module. If you find a few, buy them because they are around $300 new.
I would try redoing the wires on the distributor to ensure that they are in the proper firing order.
I would replace the distributor cap as well. Those things crack with severe weather changes, and the spark can jump around inside the distributor.
At least buy some contact cleaner and spray it out and wipe it out with white paper towels. The white towes will let you know when it's clean inside.
use some sandpaper to clean the contacts inside, and on the plug terminals.
As far as the knock goes, I have a 86 corvette longblock for $700 that runs good with a new cam and lifters and timing chain.

 

**UPDATE**
Just for giggles I unhooked the MAF plug and it ran like a top. I was even able to drive it around the block, she ran like a champ. Literally sucked gas but whatever I was just glad it moved.

I have a new MAF on order from NAPA.

Thanks guys!

 

Thats great !

You beat me to the next step.... I was going to suggest that you unplug the MAF and see what happened...the hope is that the ECM will see that as a major failure and set it to run OPEN LOOP all the time, which should be running near normally.

Your new FSM will describe what OPEN loop and CLOSED Loop mean...

basically OPEN loop (OL) is the ECM running the engine from a program thats installed from the factory. The MemCal chip & CalPak have all the necessary info to make it run but it cannot adjust or tune itself to changing conditions. Its limited in what it can do. It won;t pass a smog test for example...its unable to adapt and run perfectly.

Closed loop means that the o2 sensor has come up to operating temp and has completed the last link in the chain of sensors to "close" the loop...so now the ECM is making decisions based entirely on sensor input that must stay within a certain range...or you get the SES lite...service eng soon.

You said early on that you were not getting a SES,...I'd look at the bulb and see why. A dead MAF should make the SES lite up the Whitehouse Christmas tree in December.

Anyway, glad you got it figured out. Enjoy your car.

BTW..
sorry about the $8 confusion...I forgot that it was 85 that used the module to manage the MAF instead of relays that most other yr models utilized...relays are dirt cheap and most often whats wrong....the MAF itself was pretty reliable. The module...well, you know what that cost...GM only did that for 1 yr thankfully.

 

Well with the MAF unplugged the dash lights up like a Christmas tree. With it plugged in we get no SES light, that's a little oddball..it's almost like the computer knows the MAF is there but it just doesn't get all the data it needs from it to make the car run right.

With the MAF unplugged tho it does run like a top...sounds great, lots of power...zoom zoom. The only thing I noticed was that it was SUCKING GAS like no ones business. We started with almost a full tank and after driving around the block to get up to temp we had a little over 1/4 of a tank left. The range meter said we only had 14 miles left. HA.

I"m assuming that this is because the car is just throwing gas at the engine with no brains as to how it's supposed to adjust.

Thoughts?

PS. on the MAF actually going bad...the problem is that we have NO WAY of knowing with the PO did. We know he screwed around with it for months before dumping it. Nothing is to say that he didn't take that piece off and try to clean it, which in turn made it worse. Also coupled with the fact that when we removed the power relay it was burnt up. NO telling what kinda voltage that kid put on that line. I"ll post of pic of the relay here in a sec.

 

http://youtu.be/j-ACkbvnIAA

Here she is on her maiden voyage out of garage...haha

Just a quick video of us driving down the street.

Here is that burnt out relay
http://twitpic.com/aba3q5

Here is the shiny new relay
http://twitpic.com/aba44z

 

STOP and PARK !

That is impending disaster waiting to explode ! ! ! !

first, pull the dipstick and see if it smells of gas. See if there is TOO MUCH oil in the crankcase.

Your engine cannot burn 15 gallons of gas in as many minutes.
Its flooding the cylinders with fuel thru shorted injectors OR a blown fuel pressure regulator. Pull the vac line off the regulator and see if its wet with gas.

One or the other.;....but which ever it is you CANNOT start that engine until its fixed or you WILL hydro-lock it and it will blow a piston to pieces or send a rod thru the bottom. There is also risk of fire and explosion from the pan being full of gasoline and raw gas being in the cats/exhaust. Think about it...if all that gas was not burned, where would it be?

Either injectors OR the regulator.
Figure out which and we go from there.

 

We just replaced the FPR and the system holds a steady 39psi so I don't think it's the FPR I'll check the dipstick

 

sounds like fuel gage to me. don't see how an engine can run like a top with fuel flooding the intake.
I would verify the fuel level first.

 

You beat me to it...so I went out and looked again and I have no oil in the pan and I really don't think the injectors are stuck open. The car doesn't smell "gassy"

That being said, the car hasn't moved under it's own power in 8 months with the PO and 6 weeks with me, until last night. I've personally had the fuel pump and assembly out 3 different times, so it's entirely possible the gage is bad or the fuel level was not what I thought it was.

How is the fuel level calculated on the car? It's it a sensor or is it a float?