Problem with my 89 SC


Registered User
I've been having an issue with my 89. Every now and then, while I'm driving, it'll start running rough. When it first happened, I would just hit the gas accelerator and it would stop and continue running fine. As I said, it wouldn't happen all the time. Then it started doing it more frequently and then wouldn't stop. I'll try my best to describe what it is doing. It almost acts as if it isn't getting enough fuel. It'll shudder and the more I press on the gas, the more it'll shudder. I replaced the fuel filter already and it didn't stop it (thinking it was clogged). I've ordered a new fuel pump, but waiting on that to arrive and install. I'm going to be replacing the plugs and wires this weekend. I haven't done them yet, since I bought the car and it now has 113,000 miles on the vehicle. I'm not sure if the previous owner changed them at some point or not.


Registered User
I would check catalytic converters fuel filter as you said plugs and wires and move forward from there I've always had the mindset of start with the simplest possibilities to check and move forward from there also I'd check for leakage on the fuel pressure regulator as well

sam jones

Registered User
Good evening

Although changing a fuel pump at that mileage won't hurt it would be better to pressure test to verify. When you remove the filter did you check for heavy black debris. The tank could be compromised requiring cleaning.

There are a number of things that could cause this problem and it can be frustrating and expensive to "shoot-gun" components. Does it also spark knock and or bucks lately?

Here are some checks you could do.

Check battery power and the ground at radiator support for corrosion.

Perform scans to checks for codes.

Check spark plug wires clearance from exhaust manifold.

Remove the MAF sensor from housing and use approve cleaner. It will require a special safety torque bit.

Check the fresh air side of the pcv tube to intake duct for damage and security.

Check the pcv hoses/grommet including the attachment to the hard "y" line at the passenger side of the engine firewall for damage.

Remove DIS and check for compromised heat sink compound.

Check the following on the DIS harness:

a. The cam sensor connector for rubbing against the supercharger belt, corrosion, exposed, excessively twisted or damaged wiring. From my experience the

most common failure is at this connector requiring repair.

b. Check both the gray and black connectors for corrosion, exposed or damaged wiring.

c. Check the large gray square and crank sensor ground spade connectors for damaged wiring.

Start engine and check for vacuum leaks at the intercooler tubes and the supercharger "hat". Be careful if using flammable substance around the engine.


Registered User
the first thing that came to mind is the o2 sensors

if they arent like new then replace them regardless


Registered User
I think I figured out the problem.
So after I first got the car, I replaced the belts. I however did not replace the tensioners for the belts. So last week, I was up under the hood of the car and I noticed what looked like slippage on the belts. I also noticed that the one tensioner wasn't as tight as it should be. So I ended up ordering all three new tensioners from Super Coupe Performance and they arrived last night. I installed them today, before work. I figured I'd get new belts while I'm at it, so I went to purchase some, but they weren't in stock. I'll be able to pick them up tomorrow morning and then install them back on the car. Hopefully it was just that and it'll be back to running good again. I'll let you all know in a couple weeks. Thanks again for your help.


Registered User
I had this issue once in my 94. Check the integrity of your harmonic balancer. If the outer ring is "floating" then the timing will be wrecked causing mass bucking and performance issues. That said Sam Jones' advise is super comprehensive and should be followed.


Registered User
I got the tensioners and belts replaced and then took it out for a test drive. Of course, it started doing it. It ended up doing it twice on me. During the test drive, I stopped and checked under the hood. I didn't see anything out of place or anything that appeared to be acting up. I shut it off and let it sit for about 30 minutes (I got my haircut) and when I came back, it started with no issues. Just as I was arriving home, it started acting up again.

I'm going to go with what was given earlier and see if I can't nip this in the bud.

Tim Groth

SCCoA Member
In my year of ownership I feel on the early models 89-93 when this happens its 1 of 4 things. Harmonic Balancer about to fail, cam sensor failure, crank sensor or DIS module.

Say 75% of all issues stem from those items first.

I had a 90 SC w balancer failure it could run great 1 day break down the next did this for months until it snapped the crank bolt and left me stranded.