92 Century 2.5 liter running badly

[onetruerick]

This 92 Century only recently turned over 100K miles and ran fine until the crankshaft position sensor failed. After replacing that, it starts and idles okay, but misses badly and has very little power above 1500 rpm or so. It showed error codes for several sensors, but they were okay. I have replaced:
ignition control module
coils
plugs
timing chain
throttle position sensor
TBI injector o-rings
ECM (computer)
fuel filter

There are no error codes now. It can be driven, but not well. When trying to accelerate, it feels like the engine is not getting fuel, and I can hear a sound like muffled backfiring throught the exhaust. The exhaust system is not clogged.

Can anyone help?

Thanks,
Rick

[guyopel]

Have you checked your firing order of the coil packs ?

[onetruerick]

Yep, several times. Starting at the bottom it is 1-4-2-3.

Thanks for trying to help. Any other ideas? I thought maybe I made a mistake on the valve timing when I changed the timing chain, but I have checked and rechecked it, and even tried going one tooth in both directions, but it only made it worse.

Rick

[fueler191]

if you can, do a comp test, i bent a valve on my 90 iron duke, and had similar running troubles. i had a bent valve, pretty bad, and the car still somehow ran, but i had similar issues. If i remember correctly the fuel pump on those has the filter on/ or very near it, has the pump ever been replaced? most of the time the pump just dies, but on mine the thing accually broke..and still tried to pump but wassent sending the fuel.

But i would def check the comp on the engine, backfire could be a knock that is hard to tell where its coming from over the sound of the LOUD *** lifters on a 2.5

-jeff-

[onetruerick]

Good idea on the compression test. I don't have a compression gauge at the moment but I will get one. How did your bent valve occur? These usually happen when a timing chain fails. In my case, I replaced the timing chain, but the original one hadn't jumped, it was just worn.

I have replaced the fuel filter, the one near the tank. The fuel pump seems to be working okay - I had removed and cleaned the throttle body assembly, and put it back together with old O-rings. The fuel pressure was high enough to completely flood the engine in about 5 seconds. So bad that the cylinders filled with liquid and the engine wouldn't crank over, so I had to remove the spark plugs and crank it over to clear the gasoline out of the cylinders. I replaced the O-rings and stopped the leak, then I had to change the oil because it was full of gas!

I have tried spraying gasoline into the TBI with the engine running, holding the throttle open with the engine doing its missing thing. If it were a fuel flow problem, I would have expected the rpms to increase, but it didn't help at all.

Honestly, the engine sounds like the ignition timing is way off, but of course it can't be adjusted at all. I have tried moving the spark plug wires ahead and behind of their stock position to see if it could be the timing. All four possible positions, and it will only run with the wires in the stock position.

I have driven the car recently, and managed to get it up to 60 mph, but it took forever. At any speed, if you floor the accelerator, the car starts missing and it actually slows down!

Since I have replaced the timing chain, I have wondered if the valve timing could be off. But I have checked it, and the timing marks line up perfectly.

Question - if it were a bent valve, shouldn't the engine behave differently if I pull the plug wire off that cylinder? Or actually, if a cylinder is 'dead', it shouldn't change at all. But removing each spark plug wire one at a time makes the engine idle rpm slow down, so all 4 cylinders seem to be firing and making some power.

All ideas are appreciated. BTW, V8 Archie says that his adapter could be used to put a small-block Chevy in the car. The car would be a nice 'sleeper' with a strong 350, don't you think?

[fueler191]

my bent valve literally came out of nowhere...something should have blew up in the car a long time before then....i was 17 and was more then rough on the car (building 5 foot tall dirt ramps, and jumping it...off roading, *tour de france* which was basically power sliding with a FWD car almost drifting) but i tried to power over the snow bank that blocked my driveway, and bam, big bang, bent a valve.

If there is not bent valve, then yeah timing would be the next thing i would check.

As far as a 350 fitting, yeah an adapter would work just fine, you will have to change mounts and all that....Thinking about it...im almost 100% sure...that the 2.5 is litaraly the same thing as a chevy 305 cut in half hahaha, but like i said, you toss a 350 in there, you wont wanna beat on it...you could snap them CVs like a chicken bone with that kinda tourqe. and the tranny, well, i dont even know, it may take it for a while, but not to long i would think

-jeff-

[onetruerick]

How could I check the fuel pump pressure? When you turn the ignition switch on, the fuel pump only runs for a few seconds until the car starts. So do I check it at the fuel filter or the overpressure return line at the TBI? In my experience, electric pumps usually just fail completely, but this one has a screen on the inlet that could be clogged. It seems to be getting quite a bit of fuel, volume-wise, but I don't know about the pressure.

As far as a 350 is concerned, I think that the transaxle and axles are probably the same as in the same car with a V6. It should stand up to normal use, but probably not drag racing. These units were also used in Fieros, and if you read V8 Archie's page, he says they are strong enough for a V8. He sells the engine-to-transaxle adapter plate, and then I would need to make motor mounts, adapt the accessories to the V8, and upgrade the radiator. Shouldn't be as difficult as some swaps. For the time being, though, I would just like to get it running good with the 4.

Thanks,
Rick

[Gman]

Are you sure that the Catalytic Converters not plugged. They can melt when a car runs bad for awhile. No power indicates a plugged converter, even partially.

[onetruerick]

Well, I don't know. I removed the oxygen sensor to relieve any backpressure, and it didn't help.

[fueler191]

im still sticking with a valve train issue. As for the 350 again, sure it will withstand it, unless you have a 350 with any power behind it. And yeah it will do ok for a long while with regular driving...but wheres the fun in building an engine and puting it in a car for more power, and you never use it cause your afraid your gonna break it?

-jeff-