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1985 Corvette runs rough at idle after warm up, error 44, 45, 54

 
Air_John
V-6 Camaros rule!
Posts: 26
Joined: 08/09
Posted: 01/04/13 08:48 PM

One of our 1985 Corvettes (the black one, hers), started running rough after it warmed up, running around 198 degrees or so, not getting too hot. 200,000 miles on this one. Sometimes it acted rough at highway speeds. Passed Calif SMOG test here 4 months ago. Engine ran great until it reached operating speed. First showed an error code of 54 that is the fuel pump circuit fault or mixture control solenoid fault (not used on this engine), or ECM failure, so the book said. Pressure gauge showed fuel rails around 32 so I replaced the pump and tank filter, showing 40 now. Replaced the main fuel line filter also. Replaced the fuel pump relay and harness connector, replaced the oil pressure switch at back of the intake manifold/block (Napa OP6624 and OP6638). Replaced the spark plugs with AC Delco CR43TS, still ran like crap when warmed up, most of the time.
Then I started getting code 44 (lean mixture), then 45 (rich mixture). Replaced the Idle Air Control (Master Pro 2-IAC1 21738), got the same codes. Replace the Oxygen sensor, the one I removed looked good and was a little sooty black (BOSCH 12014). Cleared the codes again, ran OK for a few short runs, then codes 44 and 54 are back again. I ran a fresh new wire from power back to the fuel pump directly, that did not help. (Unswitched power is always hot to the oil pressure switch, then goes to the fuse panel, then to the fuel pump, the fuel pump relay is only used when starting the engine, then becomes dormant and the oil pressure switch keeps the fuel pump operating). I removed the vacuum line from the EGR valve and blocked it off, thinking it was sticking open and not closing at idle speed, same results. I can not see the operation of the EGR valve, I am not wanting to remove the plenum to get at that valve if I do not need to do that. What am I missing here?  

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waynep71222
My first time was in a Chevy
Posts: 181
Joined: 04/12
Posted: 01/04/13 10:27 PM

john...    i have a bunch of stuff for you to check....

first off....  lets look at code 54.. low voltage on the fuel pump circuit...

the fuel pump voltage circuit is measured at the ECM at pin B2    a red wire on circuit 120..

i would really like you to run this voltage drop test... first... i have found a lot of ground issues on C4 corvettes... this only takes a few minutes...  please practice this test on another car or truck to get some practice ..

print this test... follow it...  post results by number

1..___________________

2.____________________

3.____________________

4.___________________


this chart i created below is a printable image like a photograph...

~~~~~~~~~~~~~~~~~~~~~~~

VOLTAGE Drop Testing

~~~~~~~~~~~~~~~~~~~~~~~

after doing the voltage drop test on the ground i have another place i would like you to perform the same test...

using a set of  jumper cables.. black side from the negative battery post under the hood.. with the other end inside the drivers footwell so you can get at it...  the red side hooked to the Engine block someplace.. intake.. bracket.. something attached firmly to the engine block..   these are both on the negative side...

engine running... headlights on...   working under the dash board...    volt meter set to 20 volts DC...   measure the red jumper cable end to the black jumper cable end...  0.04 volts MAX...

measure the from the black jumper cable end  to the ALDL terminal A   0.02 volts max..

measure from the red jumper cable end to the ALDL terminal A ..  0.02 volts Max..

why am i having you test this...     pin A on the aldl is attached to ECM pin A12 and D3... but also to the back of the engine block.. this is the main GROUND circuit for the ECM..  there is also a separate and totally necessary ground circuit on pin *** that is attached to the back of the motor also..

yes this is complicated.. it might take you half an hour to print and run these tests...

this is the first step that i do on most cars...   code 54 is causing me to have you run the additional testing... as if you don't have a good ground for the ECM via all the proper ground connections.. you won't have enough electrons at the ECM and the signal voltages will be wrong and THROW codes at you like crazy...  including the 44 and 45..  

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waynep71222
My first time was in a Chevy
Posts: 181
Joined: 04/12
Posted: 01/05/13 04:39 AM

next is something fairly hard ..

i would like you to examine the distributer cap and the coil assembly..

you can just remove the coil cover ... unhook the bat and tach wires from the under side.. and the 3 wire connector next to them..  remove the 4 screws for the coil...

turn the coil over... check for signs of burn marks on the bottom side of the frame of the coil... where the ground strap is..

check for signs of burn marks under the heads of the hold down screws on the top of the frame of the coil...

examine the sides of the coil windings for signs of high voltage leaks...

Heicoilproblemat4k
the screws are usually 1/4" hex head.. not phillips.

COIL Highvoltageleakage

Coilhighvoltageleakareas

this is what happens of the screw that holds the black wire down comes loose.. or the ground strap under the coil gets left out..  it blows the wiring right off the coil..  this is because the ground strap completes the high voltage spark return circuit ..

Burnt Coil


if you could look inside under the cap.. but i don't know how comfortable you feel with removing the spark plug wires from the top of the cap and the ability to get them back on in the proper order so the wifes car will run...

as i would like you to also inspect the 8 terminals inside the cap... for signs of excessive build up from the high voltage arc jumping from the tip of the rotor to the cap terminals..  i would also like you to remove and inspect both sides of the ignition rotor for signs of burning thru..

with the rotor off.. take a peak down at the layers of the pick up coil...  look for signs of cracks in the magnet under the first layer... do not loosen the screws.. just look for cracks..

because this pick up coil generates low voltage signals for the ignition module .. random signals caused by cracks in the magnets will drive the system crazy...  

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waynep71222
My first time was in a Chevy
Posts: 181
Joined: 04/12
Posted: 01/05/13 04:42 AM

did you replace the oxygen sensor????  with a new one???

do you have a scan tool that displays live sensor data stream???


I would like you to the first two posts... not to skip steps...  as you can do all the other stuff i have posted.. and those can still be your issues...  and the ONLY way to check for bad grounds... is with a VOLTAGE DROP TEST with the engine running and the headlights on... so there is current flow through as many circuits as you can...

you still might end up picking up a stainless steel wire tooth brush from the hardware or paint store.  pick up one with a wooden handle..  they seem to have stronger bristles.  3 to 5 bucks.. then disconnect the battery and find the various ground connections.. including the one BEHIND THE BATTERY on the firewall.  on the inner fender under the front of the brake master cylinder..

count the number of wires on each one.. remove them.. wire brush the ring terminals on both sides.. wire brush the stud and reassemble..   there are ground cable connections probably above the oil filter mount on the side of the block.. and  on the back of the heads is where the computer harness is usually grounded...   there may also be one on one of the bell housing to engine bolts thats really really really hard to reach...

take a look at this that i threw together for the 82/84 crossfire cars...  your ground connections are very similar..

82 84Crossfiregroundconnection


see the bolt head in the middle of the green.. this is on a slightly later C4.. yes.. thats on the firewall next to the battery tray.... thats the ground connection for parts of the firewall..  a good thing to check.. but the computer harness ground connections are probably your issue or..

87 C4 Underbatterygroundconnection  

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waynep71222
My first time was in a Chevy
Posts: 181
Joined: 04/12
Posted: 01/05/13 09:52 AM

now....   you mentioned that you were worried about the EGR leaking at idle...  do you own a vacuum gauge..?  tee the end of the hose into the line that connects to the EGR valve from the solenoid...  

Th Fuelpumpvacuumtester

with the gauge layed on the wiper so you can see if while you take it for a drive.. or with the rear wheels up in the air to spin.. see if you actually get vacuum to the EGR during acceleration and during moderate and high speed cruise.. that indicates the EGR control solenoid is working..  

with the engine idling..  you can apply vacuum directly to the egr valve.. and the engine should stumble or die... that would indicate the EGR valve is working..  that model might have a back pressure type of EGR valve that has an additional diaphragm so the EGR valve will ONLY open when there is exhaust back pressure enough to close the secondary diaphragm .. this prevents the EGR system from flowing backwards and pulling intake manifold air into the exhaust...


lets look at the air injection system...

examine the tubes and pipes... the check valves into the exhaust manifolds..    this is a little harder to test..

if there are external leaks from rusted out check valves .. or rusted out tubes..  this can cause atmosphere to enter the exhaust stream before the oxygen sensor..  since the ECM uses the amount of oxygen left in the burned gasses... this is going to drive it crazy and COULD set either a code 44 or code 45.. i should know which.. but i don't recall off the top of my head..

when the air injection check valves fail.. they can allow exhaust backwards into the air injection system and burn out the plastic guts in the diverter valve...

i normally test the diverter valve by disconnecting the air injection hoses at the check valves... plugging the check valve..   plugging one of the hose ends.. so i can feel the air flow or lack of it from the other..    i have a friend start the engine.. for 20 seconds or so on a cold start..  you should have air flow .. once the oxygen sensor starts switching..  at idle. the air injection flow to the upstream tubes is cut off..   when you goose the throttle and the system drops out of closed loop.. the diverter valve should start flowing again..

if the diverter valve allows non commanded air into the upstream exhaust..  the air will dilute the exhaust stream and screw up your air fuel ratio..

.......


say... since you seem to have a fuel pressure tester.. does the fuel pressure vary depending on engine vacuum.. drop in vacuum should raise the fuel pressure 8 or 10 pounds..

this lets you know the fuel pressure regulator is working.. while you have the vacuum hose off.. it should not be leaking fuel thru the vacuum hose...  a long time ago.. a shop called me about a flooding issue..  i said.. check and change the fuel pressure regulator.. 2 sets of injectors later.. they called me again.. i went over..  pulled the vacuum hose off at the intake.  aimed it at the tech in charge as he reached through the window.. gasoline shot all over his shirt.. i said.. change the fuel pressure regulator now that it seems to be broken..

lastly... for now.. unless you have a scan tool that looks at live data stream...

engine off.. grab the throttle lever on the throttle body.. open it slightly.. look down the middle of the spring..  see if the shaft is loose in the bore...  that happens a lot..  can cause idle issues and hard start issues..  

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waynep71222
My first time was in a Chevy
Posts: 181
Joined: 04/12
Posted: 01/05/13 10:02 AM

oh... and after all the tests..

its time to RIP out the ECM...   break out the jewelers head gear and open it to inspect the circuit boards carefully for cracked solder joints.. take a look at this honda main relay..

Hondamainrelaycircuitboard


the wires get hot and expand the wire and the solder around them.. but because the heat is drawn out by the circuit board .. the center expands and contracts more than the base of the puddle..  this causes circular or tubular cracks like is seen above...

this is just the way it is...   ECMs are actually cheep now a days.. please be sure not to turn in your ECM as a core until you have verified that the new one works.. and that you have changed the PROM chip over to the new one.. and that no codes have set. after a few test drives..  

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Air_John
V-6 Camaros rule!
Posts: 26
Joined: 08/09
Posted: 03/06/13 09:59 AM

I found the problem and fixed it. Removed the ECM and found a connector pin was partially dislodged, pin D-1, one of the 12 volt connections. Next I opened the ECM and re-soldered some of the points on the circuit board where the connector pins attached there. Then I soldered pigtails onto all of the Ground wires going to the connectors, pins A12, D1, D3, and ran a heavy wire to a good Ground on the engine block. Used a very small wire brush to clean oxidation off of all the pins on the connector of the ECM. Engine has been running fine now for a week or so. It was weird to be getting one error code saying rich exhaust and at the same time getting the code for lean exhaust, and a code saying there was low voltage to the fuel pump.  

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waynep71222
My first time was in a Chevy
Posts: 181
Joined: 04/12
Posted: 03/06/13 11:47 AM

great work john...


glad you were able to get it fixed....  

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Bobs427
I love my Chevy Chevette!
Posts: 8
Joined: 02/13
Posted: 03/06/13 02:26 PM

Yeah if the fuel of the fuel pump voltage is dropping. It makes the engine go lean... Thats why it runs so good when its cold. Sounds like a MAF sensor.
200,000 miles have you ever put a timing chain in it?

Bob aka-pepsi1  

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