Dwinterberg04

Registered User
I recently purchased a 91 sc, and am having lots of problems. First off, at idle the gage shows low oil pressure. Second. The person before me cut out the cats and replaced with flex pipe. I can’t find a new downpipe anywhere. Any ideas on where to find one? 3rd, have a missfire. Think it’s because of the no exhaust but not sure tbh, and finally, sometimes I’ll be going down the road and it will randomly die. Any ideas on that aspect? Thank you very much.
 
Welcome, wow you do have some issue's. Hope you knew about them before you before you bought it & the purchase price reflects the problem's. Your next purchase should be a set of factory manuals. There are so ,any possability's for engine miss, intermittently shutting off & low oil pressure( although factory guage isn't really a guage-so unless it has aftermarket) to be guessing what your problems could be or trying to list here.
 
As Doug notes, the oil pressure guage is on/off, like a warning light...not a true pressure gauge. Find the connector to the sender and pull it off so you can polishe/clean both the connector and the sender stem - try to squeeze the connector down in size a bit, gently, so it fits back on the stem snugly. A true mechanical guage is the only way to otherwise monitor oil pressure.

Any good muffler shop can do new down pipes. SCP sells them w/o converters: 2 ¼" Down Tubes For Cast Iron Manifolds - WITHOUT catalytic converters - get prices w/shipping then then see what a shop might charge.

Random dieing is a common issue when there are problems with the front harness, and/or a bad cam sensor. Example thread: https://www.sccoa.com/forums/threads/89sc-dies-randomly.138842/

Misfires are typically plugs/wires, then maybe vacuum leaks. Feel free to search here for details.
 
I recently purchased a 91 sc, and am having lots of problems. First off, at idle the gage shows low oil pressure. Second. The person before me cut out the cats and replaced with flex pipe. I can’t find a new downpipe anywhere. Any ideas on where to find one? 3rd, have a missfire. Think it’s because of the no exhaust but not sure tbh, and finally, sometimes I’ll be going down the road and it will randomly die. Any ideas on that aspect? Thank you very much.
KMT is right. I would change out that cam shaft position sensor first. Easy job. While your at it you can look at all the cannon plugs there in the wiring bundle. CAUTION: Be careful with your CRANK SHAFT POSITION SENSOR wire and plug coming up right beside your Cam Shaft Position sensor. They don't make these anymore and a new one off the Super Coupe shop is $279 ish I think. Mine was doing the same thing. Got the Dorman from Autozone. Runs fine now. https://www.autozone.com/engine-man...rman-camshaft-synchronizer-907-965/226003_0_0
 
The miss wouldn't be caused by the exhaust. Just to be on the safe side I'd check to make sure you have good compression on all cylinders before spending any more money or time on it trying to correct the other issue's & if its good,then put new plugs & wires,in it while they are out.
 
Ant aftermarket "upgrades" that you've noticed? If done wrong that could be a culprit as well
 
Thank you all. No aftermarket upgrades from what I can tell. I know this is a long shot, but does anyone know what the sensor by the starter is? This is the only picture I have of it, but the wires are basically severed on it and I’m not sure what the sensor is. Thank you in advance. How bad are plug wires to do, I planned on changing those and plugs anyways but I’m not sure if I should do it or if I should have a shop do it. I’m decently mechanically inclined, I’ve done transmissions, water pumps and much more before but I’m not sure how bad plug wires are to do. Thank you.
 

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Looks like knock sensor. I'd do a wiring repair.

Plug wires are mostly fiddle & time consuming, but I've had trouble getting the old ones to come off the plugs. Can require doing some from below and some from above. Small hands help.
 
If the ECU can't communicate w/knock sensor, it won't be able to pull timing if/when pinging occurs. Bad pinging could be interpreted as a misfire, I think.

The ECU might decide to play it safe and retard timing as a default. This can cause driveability issues.

Have you tried reading codes...
 
If the ECU can't communicate w/knock sensor, it won't be able to pull timing if/when pinging occurs. Bad pinging could be interpreted as a misfire, I think.

The ECU might decide to play it safe and retard timing as a default. This can cause driveability issues.

Have you tried reading codes...
I aggree with KMT. I think if the ECU, loses signal from knock sensor, it defaults to a timing stratgy that keeps the timing retarded all the time. It wont cause a miss, if anything it will idle smoother with the retarded timing, but it'll be down on power-may even make the exhast manifolds glow if driven hard/high r.p.m.

Read the codes for sure though, if you haven't already done that.You should at least get one for knock not sensed during the dynamic test. If no other codes stored, basic plugs, wires & compression check is a good place to start & a good fondation since you don't know the history of the engine/car.

One of my Turbo Coupes(2.3) had a low power issue only when coolant temp was below 140, which I determined was caused by retarted timing & by unpluging the knock sensor- they are only singal wire & only send a ground signal to ECU when it sensed a knock/detonation/ping. Leaving it unplugged restored the timing to normal & the power returned. What we think was happening was too much piston to cylinder wall clearence was causing a piston slap until it got warm enough & the knock sensor was misinterpiting that noise as a knock & pulling 8 degree's timing out of it.
 
I read codes, but nothing important. Thank you all for the help. I’ll fix the wiring tomorrow hopefully and update you guys on what it’s doing
 
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