94 Caddy starts missing after driving 20 miles

[coffeeman]

Hi all

I have a 1994 Cadillac with 205,000 miles. Ran perfect till a miss developed. Not always but when it missed it stayed missing. Replaced wires and plugs. Also coil pack or coil, which ever it is. Fuel filter and thermostat too. Also replaced water pump. Someone suggested it was getting hot and that would make the computer cause the miss. Flushed the water system. The check engine light comes on sometime. But when I turn off the engine and restart; engine light off. The computer scanner doesn't show a history comming from computer. I talked with Cadillac service manager and he kind of suggested it wouldn't be cost effective to dump a lot of $$ into the car. He even suggested that he has no one in his shop that has been around long enough to know how to fix the car. I guess car is too old for their high class shop. Of course at their price for repairs he might be right. might as well junk car; way cheaper.

So the problem now; car runs great untill I drive about 20 miles without stopping. Once it starts to miss it gets progressivily worse. It never shuts down; it just chugs along on what seems to be about 7 or 8 cylinders. Check engine light doesn't usually come on even when missing. Once I shut the car down and it gets cold, it runs like a champ. Running short trips around town; no problem comes up. This car has the same engine they put in the vet that year. It's a good engine with lots of power, untill 20 miles running.

I've had the experts check this thing out; no help. Does anyone have any ideas. I know were tractor guys but.... maybe someone has an idea?

Cheers....Coffeeman

 

[kenmac]

Just a guess , I would say there is something in the electrical system that starts breaking down when it gets hot Mabe the computer. Sometimes it's hard to find fix a miss seems like you already replaced the simple things like plugs wires coil pack. Short of buying a computer see if someone can check yours or check out a salvage yard for a used computer. Usually the check engine light is an indication of an o2 sensor going bad. shouldn't make the engine miss though. Check to be sure you have good grounds no rust or corossion where the batt ground bolts to the body or bad ground cablr from the batt.Electronics require a good ground

 

[RonMar]

Does this car use a distributor cap or is it a distributorless ignition? The reason I ask is I have seen moisture in a dirty distributor cap do something similar. The moisture is in the bottom and as the engine warms, it vaporises. As it comes in contact with the colder cap, it condenses again and causes carbon on the inside to start to short out the spark causing a missfire. You shutoff and cooldown and the moisture settles to the bottom and she runs fine till she warms up. Short term cure was to pull the dist cap and wipe the moisture out with a paper towel while it was condensed in the cap. After a good(or bad) 4X4 session, I have had to stop and do this a few times to remove all the moisture from a really wet distributor.

Saw something similar on a Mitsu Eclipse my son and I were looking at on a dealers lot. We took it for a test drive and it ran great for a few minutes, then picked up a missfire and threw a check engine light. We took it back and while they were getting a tech out to look at it, I noticed water in the engine compartment from the detailer who washed it. I pulled a plug cap and saw a bit more there. It took a few minutes for the engine to warm up during our test drive and the water vapor cooking off in the plug well to get up and interfere with the spark voltage path and cause a missfire.

 

[MrJimi]

Just wondering, is that one of those that runs on 8 cylinders then switches to 6 and again to 4 for better mileage? The problem may be there
Jim

 

[RobertN]

Check the distributor cap for cracks. If there is a crack, even a hair line, it will widen as the engine compartment heats up. Then you loose sontact on one of the plug wire connectors.

Check the ballast resistor too. My old Road Runner started dying in hot wether, or while sitting in traffic. Replaced plugs, wires, rotor, cap, electronic module. Still did it. Drove me nuts! Let it sit for a few minutes, and it would start.

Turned out, the ballast resistor had a hair line crack. As it heated up, the ceramic base material expanded faster than the molded in resistor material. The Ceramic heated up, causing a break in the resistor, causing the ignition to fail. Drove me nuts! Took weeks to finally figure out... Cheap too...

 

[automech]

What Caddy, what motor? Coil over plug or distributor? I think 4.5 liters were popular in most back then. Probably old style HEI distributor. No codes eh? I will help you troubleshoot, give me more info.

 

[dbdartman]

What Caddy, what motor? Coil over plug or distributor? I think 4.5 liters were popular in most back then. Probably old style HEI distributor. No codes eh? I will help you troubleshoot, give me more info.

My '90 has the 4.5, & I' m pretty sure it was replaced by the 4.9 a year or two later. A '94 might be distributorless, otherwise it's a 4.9. Anyway, a common problem on the 4.2/4.5/4.9 engines is clogged EGR ports in the intake & build-up on the back of the throttle body blades. Both are easily fixed; the EGR ports can be reamed out with a wire coat hanger, & throttle blades cleaned with an old tooth brush & carb cleaner. Both require no more disassembly beyond removing the air cleaner intake tube & manually opening the throttle. BTW, don't worry about the carbon being pushed through the EGR ports, it'll simply end up in the exhaust system.

 

[coffeeman]

What Caddy, what motor? Coil over plug or distributor? I think 4.5 liters were popular in most back then. Probably old style HEI distributor. No codes eh? I will help you troubleshoot, give me more info.

I believe the moter is called LT1. It's a fuel injected V8; probably the biggest they offered that year. Had to replace the starter a few months ago and Advance auto gave the wrong starter. Turned out they didn't carry the starter I needed as they didn't realize some of the cars came with the LT1. Our local "mom and pop" auto parts guy knew what I needed. Don't know the liters. The car is a Fleetwood Brougham, rear wheel drive. I don't think it has a distributor as in the old days with a roter. One thing I have thought about; the fuel pump. We have replaced fuel pumps on 2 older high mile Chevy vans used at work. Fuel pumps seem to cause a lot of crazy things.

I just had the car run through emission inspection. It passed that; something that would be impossible with the newer cars. A check engine light and we have to fix it and run the car at least 50 miles before it can pass inspection.

I will be leaving my home in about an hour. Going 8 miles to daughters house for dinner. I will use the old Caddy since I have 2 grandsons, one brother-in-law, one nephew, one wife and me to transport. I also have to cart along some food, soda and 10 folding chairs. Plenty of room in trunk. Boy I like that old car.

Happy thanksgiving... Coffeeman

 

[dbdartman]

Ahhh.. a Fleetwood. TOTALLY different animal compared to me Sedan DeVille.

 

[Tig]

I had a 1990 GM product, different engine. It would warm up and die after about 15 miles. No codes. Factory service manaual listed ignition pack, computer etc. I used an oscilloscope to track it down, It was the crank sensor. On the scope you could see a healthy signal of about 1.5V p-p deteriorate to below a volt then die. When I removed the sensor I could see a hairline crack.