Hello guys,

Since this is my first post i will introduce myself first:
My name is Joerg and iīm living near Frankfurt, Germany. I have 3 B-Bodies, a modified 91 Caprice 9C1, a 96 Caprice 9C1 and a 91 Oldsmobile Custom Cruiser. The Olds has the L03 and it is my daily driver. It has 136000 miles on it. I bought it 4 years ago with 94000 miles. Iīm posting in a F-Body forum because all the TBI guys are here. Hope you can help.

Never had a problem with the Olds until now. A few weeks ago the L03 engine started to have a rough idle and to stumble and backfiring through the TB under load. The next day the car runs just fine. It happens mostly after it was not driven for a day. After reading here a little bit, i replaced the EST and the pickup coil. During the disassembly i noticed corroded contacts in the cap and on the top where the wire plugs are going to. I replaced the spark plugs, cap, rotor and wires approx. 20000 miles ago. I forgot to put on this grease stuff and this caused the corrosion i think.
I cleaned the all the contacts and put everything together. The rough idle was gone but it still was stumbling. After accelerating a few times the car did run very nice. Later then, after the car was sitting a day or so, the stumbling and backfiring was back. It is really annoying because i know the car will not run properly after i did not use it for a day.

I tried another O2 sensor but it did not help. I already replaced the MAP sensor as well. I have a new TPS here but i donīt think it will help. The fuel filter is 5 months old.
Next week i will replace the plugs, cap, rotor and wires again but i think it is fuel related. Is my fuel pump dying? I canīt check the fuel pressure right now because i would have to order a gauge in the US.

What do you guys think? Will a new set of plugs and wires help or is it fuel related?

Thanks,
Joerg

 

Probably fuel related . Could even be some air in your coolant faulsing your coolant sensor ...

 

Thanks golden.

hmm .. the engine has a slight coolant leak at the intake manifold gasket, above the water pump. It was there before i bought the car and it is so tiny that i never thought of replacing the gasket. Iīm just adding 1 qt of coolant in every few months and never had overheating issues, but a few weeks ago there was a coolant puddle on the intake manifold, in the area were the leak is. Can the cooling system suck air through a leak?

 

It may not be a bad idea to replace the plugs, cap and rotor bit I wouldn't replace the wires if they are relatively new and don't have any signs of damage or wear. When you pull the plugs inspect them for signs of coolant and or other problems that could cause a missfire. You are going to have to replace the intake gaskets sooner or later and that leak will only get worse. It would also be a good time to check your base timing. If you have been messing around the cap and wires you may have accidently bumped the ditributor around cuasing the timing to be off. Unplug the EST and with the car at idle make sure that the base timing is around 0°. Back firing through the TBI is mostly timing related.

 

Also change the fuel filter

 

It also wouldn't hurt to check the resistance of the spark plug wires with an ohm meter. Even new spark plug wires can be bad. It only takes a few seconds to check.

 

After i was done with the work on the distributor I set the base timing to 0 degrees with EST unpluged. The fuel filter is less than 10000mls old but i will replace it again if i need to replace the fuel pump.

Yesterday the car was running very nice. Today, on the way to work the stumpling was back.
Everything looks fine until i push the pedal more than half throttle, -to accelerate when entering the Autobahn or to pass other cars, for example. The backfiring happens only when i push the pedal further down while the engine is stumpling. But i can cruise at 80mph with no problems.

 

have an update:
The last time i used the car was the day before yesterday and today itīs not even starting. The fuel pump sounds like itīs not spinning that fast anymore and it runs much longer than usual when i turn on the ignition.

Bad thing is the new parts are still on transit.

Good thing is i had to use my wifeīs 96 9C1 to go to work today

 

Hello!

Hereīs an update:

Looks like the new Fuel Pump i ordered got lost on itīs way to Germany. I ordered a second one a few days ago. So the car is still sitting in my yard and doesnīt start.
When i crank the engine, The Fuel Pump runs, the injectors are spraying and i have spark on the #1 plug and the rockers are moving. At this point i really donīt think the FP will help. Even starter spray (this ether stuff) doesnīt do anything.
When i try to start the engine it sounds like some cylinders are fireing now and then, but thatīs all.

Does anyone have an idea?

 

check your timing. you just messed with the distributor, right?

if you think the fuel pump is gone bad, hit your fuel tank with a hammer from underneath the car while someone cranks the car over. it can cause the fuel pump to start working again (usually only momentarily)...but you said the injectors are spraying so forget that

 

Maybe try a different ecm?

 

Today i bought a new ignition coil and installed it. At first the engine didnīt want to start and the battery was going tired. After the battery was recharged i started the engine with WOT and after some cranking it was running but died at idle. On the third attempt it started and kept running, but very rough and crappy. I think the plugs were wet and dirty. After 20 miles with some WOT on the Autobahn it runs like a champ now. Now i hope it will still run like that when i will drive it tomorrow.

 

Sorry for replying to this old thread, but it turned out it wasnīt the coil. After the car was sitting a while the proplem was back. A week ago i installed a new Fuel Pump and this was the final solution!!