Car is a 94 sundance, 2.5 TBI. 75k miles.

Has NO egr system, as I see nothing hanging off of the intake.


Car ran like crap since we bought it, and then decided to eat the headgasket. Gasket is replaced along with: TB gasket, Intake gasket, head washers/bolts, wires,plugs, cap/rotor...

Car idles PERFECT, it's never idled this nice. Off idle driving around, it falls flat on it's face. Cam timing is one tooth advanced, and compression is right at 130psi. I don't have a timing light here to set ignition timing, but the distributor is sitting flat across as they normally are.


It feels like a lean spot. Coming off a stop light, it wants to get the revs up and then it falls on it's face and takes forever to get upto 50mph.

A Guess list:
-Plugged Cat
-Bad coolant temp sensor
-leaky injector (maybe)
-MAP sensor
-O2 Sensor
-TPS
-Clogged fuel filter/ weak pump

Can someone narrow that down?

 

Advanced the timing a bit (little less then 10 degrees by eye) Must have been a tooth off when setting it.

Runs like a champ at WOT. Feathering the throttle to get to speed, it sputters.


I'm thinking plugged cat, as it was running ROUGH before all this work. By law I do not need a cat (nor does MI check for them) Will the ECU/O2 Freak out if the cat get's cut out? I noticed no downstream o2, so I should be fine?

 

The easiest way to test for a plugged cat is this, get it up to temp, and put your hand on the ground below the cat DO NOT TOUCH THE CAT, if you feel excessive heat or if you feel a lot of heat coming from under the car in the area near the cat it may be plugged, next with the engine running ball up a rag and hold it tight on the end of the tail pipe, hold it there for a couple seconds and pull it away, if the cat is good you should a strong puff when the exhaust pressure is released, if its bad the puff will be weak.

If the cat checks out ok I would change the fuel filter, and check the fuel pressure at idle cold, and at idle at temp, though rare on FI systems you could have vapor lock. To combat vapor lock wrap the fuel lines near any heat source in aluminum foil, the foil works I had to do to a 48 Studebaker I owned and it cured the problem, the foil trick was told me years ago by an old school hot rodder.

 

Changed the fuel filter. Just so happened to order one from rockauto when I ordered all the other goodies.

Didn't do much.

Cat does get warm, but not glowing. Plenty of flow out the back when doing the rag test.

ONLY starts acting up when warm. Runs perfect until then. Idles like glass.


-TPS acting up
-Map acting up (but runs fine when cold?)
-Intake air temp sensor (is this car equipped with one?)
-Cat (does indeed get warm...)
-Fuel pressure (need to get a test kit here)
-Converter locking up at low speeds (odd to happen, but could explain EVERYTHING)

Car runs perfect until it's under load. Revving it is smooth as glass.



This thing's driving me crazy!

 

Next thing to check is fuel pressure, I am going to have look up the specs for pressure, I have to dig out my trusty repair book. I would also check to see what the coil is putting out, you may also have a bad coil.

 

I'm about to push this car off the nearest cliff.


It's not the map, Changed it - did not help any.


I don't see how it would be a coil, it does not feel like it's dropping spark at all. I'm leaning towards a TPS or a bad gasket in the TB. Could also be a weak pump/bad regulator, but the pump isn't loud and how often do you see regulators fail?

Car also runs rich at idle, but the idle does not drop out like it did. Runs great at WOT also - this is leading me to a TPS issue.