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Help with misfire

172 Views 12 Replies 2 Participants Last post by  simplydarkness
This is gonna be a little long, but details are important. 1996 Cadillac Fleetwood brougham 6 door eureka coach. I drove 5k miles to move, he drove smooth. Got to the mountains (200 elevation to 10k elevation) and his transmission pan popped like a bag of potato chips. Waterfall, so I tightened it up, and added fluid. 3rd and 4th completely gone, could drive it to 45mph then goes straight into neutral.馃槶
So for 10 months I drove him around the block bi weekly until I saved enough to get it fixed. Took it to a great shop, rebuilt it to heavy torque truck specks, shift kit, everything. But something went wrong....
They ran it out of gas on test running it, added gas to continue, and throwing codes P0175, 0300, 1380, 1381. So they switch the 02 connect on passenger side, to make sure. Still throws codes. I got it back, 02s are correct side connects, 0175 goes away. Still get 0300 and 0304. So pull the plugs, clean them and swap 3-4 plugs to check. Still says misfire on 4th cylinder. Tested vacuum on fuel pressure regulator, has vac. Pulled clips on injectors, they responded. I put Lucas Injector cleaner in with new gas. I've been going through this for a week now and my appointment for the tag is next week and I need it running smoothly for the state inspection. What could this be and what do I need to check? Thanks
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How is the pressure on your fuel pump? I see you tested the regulator, but if the pump is not giving you full pressure, it could certainly cause a miss.

Of course, if that isn't it, you can also have an issue with the ignition system. Opti Cap and Rotor problems can manifest in all sorts of ways.

Good luck getting it running and tagged! Hoping to hear more.
How is the pressure on your fuel pump? I see you tested the regulator, but if the pump is not giving you full pressure, it could certainly cause a miss.

Of course, if that isn't it, you can also have an issue with the ignition system. Opti Cap and Rotor problems can manifest in all sorts of ways.

Good luck getting it running and tagged! Hoping to hear more.
I don't have a way to test the pressure, and it's a huge tank, 22 gallons. My uncle wants to check stuff like EGR, tps, fuel pressure regulator, injectors. But why would it show only on one cylinder? I don't want to just replace parts
I agree that it would be best to avoid just changing parts. I prefer to have a known answer when I spend my money.

You can get a fuel pump tester fairly cheap at most parts stores. Fuel pumps are a pretty common issue, at least on the f body side, and it would allow you to know. If your pressure is just below spec, it could cause a misfire on a cylinder that may be slightly less than ideal. Testing for this is much easier than getting to the opti spark to inspect the cap and rotor.

Past that, I would go to the usual ignition suspects. Wires, plugs, coil, ICM and optispark.

Shbox 4th gen aids.

That link has the testing procedures for almost everything you could need on an LT1 equiped vehicle. This should help you narrow down your suspects until you get the answer.

PS.
You can check the Fuel pressure regulator by disconnecting the vacuum line, and giving it a sniff. If it smells like fuel, the regulator needs replaced.
I agree that it would be best to avoid just changing parts. I prefer to have a known answer when I spend my money.

You can get a fuel pump tester fairly cheap at most parts stores. Fuel pumps are a pretty common issue, at least on the f body side, and it would allow you to know. If your pressure is just below spec, it could cause a misfire on a cylinder that may be slightly less than ideal. Testing for this is much easier than getting to the opti spark to inspect the cap and rotor.

Past that, I would go to the usual ignition suspects. Wires, plugs, coil, ICM and optispark.

Shbox 4th gen aids.

That link has the testing procedures for almost everything you could need on an LT1 equiped vehicle. This should help you narrow down your suspects until you get the answer.

PS.
You can check the Fuel pressure regulator by disconnecting the vacuum line, and giving it a sniff. If it smells like fuel, the regulator needs replaced.
As far as being an f body, I don't know, it's a 23' limo. There's been some modifications by eureka coach. It has the 14 bolt differential. I know they replaced the tank from a 17 gallon to a 23 gallon with the bra strap. So that might be a totally different pump system. It only bogs in gas at low gears when hot, when past 30 mph it's smooth. I'm waiting for dusk to pull the plug on 4th cylinder and look for spark. Thank you very much for the link, I'll get on that tomorrow to check everything else out.馃憤
I agree that it would be best to avoid just changing parts. I prefer to have a known answer when I spend my money.

You can get a fuel pump tester fairly cheap at most parts stores. Fuel pumps are a pretty common issue, at least on the f body side, and it would allow you to know. If your pressure is just below spec, it could cause a misfire on a cylinder that may be slightly less than ideal. Testing for this is much easier than getting to the opti spark to inspect the cap and rotor.

Past that, I would go to the usual ignition suspects. Wires, plugs, coil, ICM and optispark.

Shbox 4th gen aids.

That link has the testing procedures for almost everything you could need on an LT1 equiped vehicle. This should help you narrow down your suspects until you get the answer.

PS.
You can check the Fuel pressure regulator by disconnecting the vacuum line, and giving it a sniff. If it smells like fuel, the regulator needs replaced.
Just pulled the wire, no spark on 4th. So it would be the Opti not firing?
If you are firing on other cylinders, the Opti is still at least partially sending spark. I would check wires, and look for spark leakage. Best to do at night. Use a spray bottle, and spray the #4 wire while running the engine. In the dark, if the plug wire has gone bad or is compromised, you will see arcing in the dark. If that doesn't show anything firing off, you may have to do a cap and rotor. I would hate to send you down that path right away, mainly because it is a pain in the backside, and also quite expensive.

Out of curiosity, when was the last time a tune up was done? It just may be time for some of these parts to be replaced. Just want to make sure we chose the right ones.
If you are firing on other cylinders, the Opti is still at least partially sending spark. I would check wires, and look for spark leakage. Best to do at night. Use a spray bottle, and spray the #4 wire while running the engine. In the dark, if the plug wire has gone bad or is compromised, you will see arcing in the dark.

Out of curiosity, when was the last time a tune up was done?
I did almost everything 2 years ago. Plugs, vac lines, purge valve solenoid, water pump, all new hoses, belt, starter, alternator, even u-joints in the double drive shaft and all brakes/tires. I think the only thing I haven't is Opti and fuel pump.....
I have 10 year plugs, I've already removed and cleaned them. Even swapped 3 and 4 out to make sure it wasn't spark plugs. Water pump was a year and a half ago, so if it did mess up the Opti it would of faulted out sooner.
I did almost everything 2 years ago. Plugs, vac lines, purge valve solenoid, water pump, all new hoses, belt, starter, alternator, even u-joints in the double drive shaft and all brakes/tires. I think the only thing I haven't is Opti and fuel pump.....
I have 10 year plugs, I've already removed and cleaned them. Even swapped 3 and 4 out to make sure it wasn't spark plugs. Water pump was a year and a half ago, so if it did mess up the Opti it would of faulted out sooner.
Well......... I found it. The dreaded Opti spark is cracked at the connector, accidentally bumped the harness to it and it bogged out. Looked and the whole connector moved the plastic of the Opti, it's gone. So, where do I get one that's reliable and not pricey? I see a lot of bad review out there.....
Hate to hear about the bad luck there. You may get lucky on ebay, but the last time I looked ( about 6-8 months), there were a couple NOS Delcos, but they were all spline drive, so less than helpful here.

If you are a gambling man, you can try car-part.com. I have had pretty good luck with engines and transmissions, but you likely wont get to see the opti prior to purchase. The draw is that I have seen some as low as $40. There is also contact info so you might be able to reach out and ask questions first.
Hate to hear about the bad luck there. You may get lucky on ebay, but the last time I looked ( about 6-8 months), there were a couple NOS Delcos, but they were all spline drive, so less than helpful here.

If you are a gambling man, you can try car-part.com. I have had pretty good luck with engines and transmissions, but you likely wont get to see the opti prior to purchase. The draw is that I have seen some as low as $40. There is also contact info so you might be able to reach out and ask questions first.
What about parts geek? They have some OEM for about $120.....
If that is an AC Delco or Delphi for that price, buy 2. If not, be very wary. Tons of "OEM" quality ones are just manufactured garbage. Even stuff like the MSD Pro Billet is hit and miss.

The best option is a true GM Optispark, as stated above, those are going to be the Delco and Delphi. Next to that, I have heard good things about Petris Systems Optis, but they carry a hefty premium.
If that is an AC Delco or Delphi for that price, buy 2. If not, be very wary. Tons of "OEM" quality ones are just manufactured garbage. Even stuff like the MSD Pro Billet is hit and miss.

The best option is a true GM Optispark, as stated above, those are going to be the Delco and Delphi. Next to that, I have heard good things about Petris Systems Optis, but they carry a hefty premium.
Well, there's more!!! I ended up getting a Opti from AutoZone with lifetime warranty. The harmonic balancer pulley is mandatory!! Finished and still misfiring, so look at live data for 02 sensors. Passenger upstream kept running way high, we thought from the rich bank 2, and figured out upstreams were reversed. Driver/passenger side. Fixed that, burp the coolant. Day 2 and still purging? It's still overheating, #24 on the AC is supposed to hover max at 95掳. That's where the overheating fan comes on. It's going to the max stat at 125掳. It hasn't blown anything. I burp, cool and refill.....what's going on? New water pump and thermostat last year, and they work.
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