Help! 94SC blowing black smoke won’t idle and hesitation!

rwferguson

Registered User
1994 SC has been upgraded with a built bottom end. The car is very familiar on this page. My Dad recently toke the car to the shop to get some things fixed and checked. The shop replaced the sending unit in the gas tank among other things. The car ran great prior to dropping it off to the shop. When the shop tried to use the obd1/2 port they stated they weren’t getting a connection to figure out why the CEL is now on.
So here’s our problem!

The car acts like it’s a miss fire, horrible hesitation, won’t idle, and have to use starting fluid to get it to start.

when it’s running it dies if u don’t back the gas off slowly. We just changed the plugs and still no change. I noticed a vacuum line that broke and fixed it but still no change. The car doesn’t have an egr valve and is spitting out black liquid which smells like raw fuel. We also replaced the MAF thinking maybe that was an issue because when we unplugged the old MAF nothing changed. Something is horribly wrong with the poor girl and I’m visiting my dad hoping to get her up and running again. Now the plugs were coated it black build up! What I think is happening is the car has default to full rich dumping too much fuel into the engine and blowing spark out. I’ve did some poking around on the forums and may have narrowed it down to the following:

Fuel pressure regulator
O2 Sensor
ECU lost the tune
Bad ECU
Vacuum leak
Clogged IAC

so any help would be much appreciated!! We have been members for 10+ years maybe even longer tbh. I’ll post a video on YouTube so y’all can also see what’s going on. I’m hoping somebody can help pin point this problem. Thanks in advanced for any help and anything right now is much appreciated because we are completely stumped. The shop can’t even figure it out as well
 

sam jones

Registered User
Good evening

Start with a visual inspection.

Check the coil pack to DIS harness connectors for security.
Scan KOEO codes.
Check the catalytic converter. Lightly tap with a rubber hammer to listen for broken honeycomb structure causing blockage.
Check oxygen sensor body, connectors and leads for damage.
If you have an infrared thermometer gun check inlet and outlet for suspect blockage.
See attachment


Eliminate fuel pump as cause.
Check fuel pressure. If not within specs suspect tank contamination, fuel pump defects (fuel pump sox damage, fuel pump outlet hose, cracked fuel pump baffle, fuel pump connector/harness).
Remove the fuel filter. Pour remains from inlet/outlet on a clean white paper towel. Check for contamination/ debris. If so remove fuel tank and clean inside.

Use attachment as reference.


.
 

jb351

SCCoA Member
Is the engine stock or are there any mods to it?

You need the trouble codes from the EEC unit. It is OBD-1 and a cheap scan tool can get them for you or you can count the flashes with a test light or on the CEL.

Does the vacuum line on the fuel pressure regulator smell like fuel? If so the diaphragm on the regulator is leaking.
Change the fuel filter.
Check the TPS sensor/voltage.
Confirm the correct firing order on the coil pack. One of the manuals out there (Hayes I think) has the incorrect one listed for the SC.
What plugs and wires are on there now and what condition are the wires in?
Try cleaning the IAC valve and have the computer relearn the idle.
Check and test very thoroughly for vacuum and boost leaks.
If it will idle how much vacuum is it pulling and at what RPM?
 

rwferguson

Registered User
So the engine is not stock it has internals upgraded sc housing, TB, all the parts came from Supercoupe performance.com. So we check the fuel pressure and the results were dead on within specs. So here’s what we know.

fuel pressure regulator- Good
Spark plugs - Good (Replaced)
Firing order - Correct
MAF - Good (Replaced)
CEL is on still

so here the problem. I just tried to read the CEL using the jumper method on the OBD1 port under the hood. Nothing happens! The CEL doesn’t flash or do anything. I’m starting to think it’s an issue with the ECU. Cause the car is full rich and dumping fuel like crazy! It’s fouling out the plugs and has fouled the o2 sensors. What’s even weirder is when we u plug the MAF the car doesn’t die it keeps running like crap. Unplugging the MAF does absolutely nothing. Any ideas? Thanks in advanced
 

35th

Registered User
Watched your video and I'm not at all an expert by any means but it sounds like mine did when my computer went bad mine was leaking rain water at the fresh air vent under the cowling fixed the leak replaced the computer ran fine I'd ve inclined to tell you to take the advice of some of the other member because their knowledge super exeds mine but that's where my opinion is best of luck to you
 

KMT

Registered User
Which is NOT a Symptom of a Potentially Bad ECT Sensor
  • Continuous rich air-fuel mixture
  • Continuous lean air-fuel mixture
  • Rough idle
  • Engine misfire
  • Engine stalling
  • Increased emissions
  • Increased fuel consumption

Answer is: misfire
 

Tim Groth

SCCoA Member
Give me a little more to work with on this one. I assume when it was delivered to the shop it did not run? Or did it run fine they replaced the fuel sender and now we are here?

You mentioned performance mods from SCP.com ...what exact mods do you have?

Usually in my experience these cars dump fuel if there is a vac leak, but the engine shouldn't have been touched at the shop.

Help me with the back story.

-Tim
 

KMT

Registered User
Answer is: misfire

Missed the edit window... part 2.

Keep in mind that issues with corroded connectors/wiring, failed connectors due to misaligned/plunged pins, incorrect reference voltage, and bad/missing grounds can cause an ECT to send incorrect values back to the EEC - I would pull the connector, verify it's health, then, if the ECT is years old, replace it just to take it out of the picture. Search here on previous discussion on 5v reference voltage troubleshooting.

Otherwise, I agree on the chance of a big old vacuum leak.

Good luck.

Ken
 

Tim Groth

SCCoA Member
I keep re-reading the first post and grabbing more info and also answering my own questions.

Tell me more about the tune. If it has a quarter horse chip with a tune the tell they are bad is key on the fan kicks on high. When my chip failed in my 95 it acted a lot like that video now that I think about it (this was around 2015 ish) so memory is only so good.

I've convinced myself at this point it's the tune lost or is a QH chip the battery has failed.

-Tim
 

rwferguson

Registered User
Give me a little more to work with on this one. I assume when it was delivered to the shop it did not run? Or did it run fine they replaced the fuel sender and now we are here?

You mentioned performance mods from SCP.com ...what exact mods do you have?

Usually in my experience these cars dump fuel if there is a vac leak, but the engine shouldn't have been touched at the shop.

Help me with the back story.

-Tim

so the car ran perfect. The shop replaced the fuel pump and the sending unit and at this point the car still ran fine. They replaced the master cylinder and replaced the clutch slaver cylinder that’s when the issue of the car running poorly. It was running rich after they installed the fuel pump and the shop tried to connect to the ECU but couldn’t connect to it. The car left running in the current state (link to the yt video).

mods:
Bottom end is fully built
Has larger supercharger
Larger TB
Pullies
Stock manifolds
larger plenum
Oversized griffin radiator
Fan for intercooler
Dyno tuned by David Dalke
Egr valve delete
 

rwferguson

Registered User
I keep re-reading the first post and grabbing more info and also answering my own questions.

Tell me more about the tune. If it has a quarter horse chip with a tune the tell they are bad is key on the fan kicks on high. When my chip failed in my 95 it acted a lot like that video now that I think about it (this was around 2015 ish) so memory is only so good.

I've convinced myself at this point it's the tune lost or is a QH chip the battery has failed.

-Tim
So I absolutely agree Tim! I think either the ECU has fired or the ECU tune is gone. So we need to get in contact with Dave Dalke (last name) might be incorrect. But he super known on this forum. I thought his username was xr-7 or something of that extent. We do still have documents he provided my Dad for the dyno tuning sessions, tuning, etc. so if anyone can PM me his contact info we would appreciate it so much. Dad is about to spend over 3200 bucks to have another shop look at it but I keep telling him don’t we could use that money to upgrade the car more. He is just super frustrated and to be honest I am an ASE certified mechanic but this is beyond my knowledge and feel with the forums input/support/knowledge we can surly figure this problem out. Thank you all for everything, all the ideas, bouncing ideas off each other! This is what a forums about and we are so grateful to be apart of this community.
 

rwferguson

Registered User
Update! Well we got a lot of rain in GA I just checked the passenger floor board due to a post I read about it happening to another member. Sad to say but the passenger floor board and carpet are soaked. Water is coming in from the cowl. At this point we are pulling the ECU to see the damages.

Dad is going too order a new ECU and we will be reaching out to Dave to have him reprogram the tune on the ECU
 

rwferguson

Registered User
Update! Well we got a lot of rain in GA I just checked the passenger floor board due to a post I read about it happening to another member. Sad to say but the passenger floor board and carpet are soaked. Water is coming in from the cowl. At this point we are pulling the ECU to see the damages.

Dad is going too order a new ECU and we will be reaching out to Dave to have him reprogram the tune on the ECU

Update:
Sorry everyone we have finally confirmed the Moates Chip lost battery power and we are assuming we lost the tune. I disconnected the chip from the ECU and reinstalled the ECU. The Supercoupe is now up and running! Night and day difference. The CEL is off rn but we know it’ll come back on. We are trying to get ahold of Moates to see if they will let us upgrade the chip with one that has a replaceable battery. We have reached out to Dave from Super Coupe Unlimited for assistance as well. Wish us luck! We are super thrilled rn. We have done some research and there’s a possibility even though the chip has a dead battery the tune is still in the memory. Trying to talk Dad in letting me replace the BR2330A battery with the CR2032 battery. If by chance anyone knows how we can replace it please let us know also if you know about if we lost the tune or not. Again!! Thank you all for everything you have no idea how much this means to my dad rn. He is going through a very hard time in life rn and this car is something he loves. Again i can’t thank y’all enough for all the support, ideas, comments, and even people who read the thread but didn’t know thank you. This is an amazing community and I’m so grateful for all of you!! Hope you and your family’s stay safe.
 
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