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94 fleetwood idle prob.

6K views 31 replies 7 participants last post by  slayu2day 
#1 ·
I have a 94' fleetwood brougham with the 5.7 with the performance chip. Also, all pollution control has been removed. Dual exhaust with blow-through cats. Aftermarket computer to run it stripped down like it is. Its been trouble free for the last year or so, but sometimes it just dies at idle or no excelleration like if pulling into a gas station. I can tell when its going to do this by the way the idle seems low. If I'm running the a/c, the fan will also slow when pulling up to a stop. I have 3 guages on the 'A' pillar. Water temp, fuel pressure and air/fuel mixture. The air/fuel mixture leans out alittle along with fuel pressure drops a couple lbs. If the car stalls, it starts right back up on a dime, but may continue to act this way. But most of the time the car is great with no stalling. I would like some other opinions on what this could be. I am thinking maybe fuel filter ... or maybe the pump. But the car never boggs at any excelleration or start-up .. so I'm not sure if its a fuel issue or maybe the chip or cpu.
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#3 ·
And the "aftermarket computer". Seems to be a contradiction in terms.

Irrespective of what you're using for engine management, if it ran fine before and doesn't now then something has changed or failed.

The A/F "gauges" really aren't very accurate - they'll change with fluctuating voltage. But, if your FP is dropping as well, and your fan(s) are slowing down, you may be having an intermittent electrical problem. I'd make sure your battery terminals are clean and connections are tight.
 
#4 ·
Heres a performance chip description from autochips direct.

Our Cadillac Fleetwood Performance Chip utilizes the latest in performance technologiy. PowerBOX Chips send a unique modified signal through an engine data sensor. This signal causes your factory Engine Control Module to reprogram itself for a more efficient air/fuel ratio and timing curve. By doing so, we're able to safely unlock up to +75 Horsepower and up to +8 MPG in your vehicle!
Our modules never bypass, deactive, or exceed factory limitations. That being said, this is perhaps one of the safest upgrades you can do to your vehicle!
 
#6 ·
I'm siding in here with tubrojimmy when he says you might have a electical problem... I'm going to bet that when you are having your problem your voltage to the computer is dropping..A bad connection or a short could do this.. this is what i would look for..I think you can get the voltage off the dash CCU .. anyone know the right window to look at?
 
#7 · (Edited)
Are you saying all mod chips are the same way ? Even diesel chips ? Because I have seen major improvments in cars and trucks, ( performence and power), when they have put a chip in. I do not know what kind or model or anything about the chip in my caddy. I bought it with it already installed. Also has a huge cold air intake tube and filter sucking good cool air. That description of the chip I posted was just a random internet store description.
Most of the time its just fine, and its faster than almost everyone expects it to be. The 373 gears in the rear-end help with that. LOL No lights dim when it idles low, no dash lights dim, only the fan will slow up some.
I agree it could be something electrical, because remember, alot of electrical stuff has been removed under the hood. Its pretty bare bones under there.
So I'll keep troubleshooting this issue, but it only does its stall-low idle crap occationaly. It can go months with no issue, but then 3 times in one week. So it will be tough to track down.
 
#8 ·
No, not all mod chips. Just the LT1 "chip". It isn't a chip. It's useless. Trust me. Show us a picture of this "chip". If you think it is in the computer, I'm sorry, but someone gave you a load of BS. The PCM (computer) doesn't use "chips". It has programmable flash memory. You said you have a performance computer. What's in the tune? Who did it? Step one: remove your "chip" (if you even have one, look on the MAF connnector, but I suspect that you were told bogus info and you don't actually have a "chip") Step two: find out what's the tune in your PCM (what was changed: timing, shift points, fuel tables, etc, etc)
 
#9 ·
There are two different computers under the hood. They are pretty big each. There is also one in the trunk for the body roll and leveling. One thing, the guy I bought it from is a gearhead. He builds engines for big rock crawler trucks, he also does cars. He really does know quite abit about wrenching.
I will post a pic of the ones under the hood probly sometime today, Monday. And its not a performance cpu, its one that will run the car without pollution control crap. But I don't know why there is two of them.
I am more of a mechanical side of working and building cars. So this electrical stuff is kinda new to me. I appreciate the help.
 
#11 ·
The one computer under the hood is the one under your air filter. That is the PCM (powertrain control module). That's the only computer up there. The one in the trunk is the BCM (body control module), but it has nothing to do with body roll and level. This is what the PCM looks like. It will have four wire connections on it.
 
#13 ·
I will tell you that on my 1994 FWB,after I installed the new Opti,and a new water pump, I had a idle issue. Sometimes it was fine and then sometimes when you would pull up to a stop sign,the car felt as if it was running at 4000 rpm's and felt as if it was going to shut off. After installing two new O2 sensors,no more problems,and MAN what a differance in fuel mileage. Totally differant car.
Just a thought
 
#14 ·
yea I have that pcm with the 4 plug-ins, and I was mistaken, theres only one unit there, looked like 2 because it doesn't have that metal shrowd. But on mine, I have the big cold air tube running down by front left. All that black plastic is removed from top of my motor. So the pcm is on the left front inner fender. I am sorry I keep forgetting to get a photo of under hood, but I changed my fuel filter and my fuel pressure came back up , but occationaly getting low idle, but if I drive it on the highway a few miles, the idle issue clears up. Do you think that mod chip or card is in the pcm ?
 
#20 ·
Well I'm not sure, thats just what autozone says is for 5.7 94' fleetwood. I will just gut the whole darn thing out and drop a freeking crate engine in it and call it done... LOL All in all its running pretty strong with only this minor issue. I'll get more info soon.
 
#22 ·
He he he for sure, I know how the autozone guys are. They know as much as the computer screen will tell them...LOL . Oh and by the way, I talked to the guy I bought caddy from and he said its the flash inside the PCM . Maybe I need to have the PCM programmed again ? Is there a way I can check the PCM for faults ?
 
#23 ·
Ok, well I'm starting to understand and learn about what the hell this car does have and does not have. Its my 1st 5.7 LT1 , mechanicaly I am fairly good about things, but electronics are just not my thing. All I know is the caddy moves alot faster than it should with just some bolt-ons. I think thats alot to do with the 373 rear-end gears. Other caddy's can't keep up with it, unless they are turbo-charged or something along those lines.
 
#24 · (Edited)
The gears make a huge difference, particularly off the line.

The '94-95 LT1 engines are controlled by the Powertrain Control Module (PCM). It's a PROM (Programmable Read Only Memory)-based piece of electronics that manages all of the fuel and timing events for the engine. The PROM (or EPROM - erasable programmable read only memory), as the name implies, is programmable. There are different types of PROMs - early ones are actual chips, later ones are components soldered to a circuit board. With the advent of PROM-based PCMs, auto manufacturers could use the same piece of hardware to control virtually any drivetrain that they manufacture. They "burn" the PROM with information about that vehicle's specific configuration (engine, transmission, weight, axle ration, options, etc) and pop it into the PCM. The PROM is the "chip" you posted a picture of. In the early days, you would get one custom burned for your application. I had a glovebox full of them in my Grand National - one for street 87 octane, one for street 100 octane, one for the track 110 octane, one for the track 114 octane, one for the street 93 octane w/ alcohol, etc. and so on. I would leave the cover off the PCM so I could swap them out easily.

Eventually I moved to a FAST (http://www.fuelairspark.com/) system in the Grand National which is a lot like modern PCMs - they can be reprogrammed over and over again using a laptop and don't have "chips" in them anymore. If I wanted a specific tune, I would flash the PCM with the laptop - it would take about 15 seconds. Run it down the track, check the logs, make adjustments and upload them to the FAST module. This is a good segue into what our Cadillacs have in the way of PCMs.

I haven't taken our Cadillac PCMs apart, but based on Jay's response and my own observations, I would assume that our PCMs have EEPROMs in them. EEPROM is defined as Electronically Erasable Programmable Read Only Memory (EEPROM). The EEPROM is soldered to the circuit board and can be electronically erased and reprogrammed over and over again. It makes it even easier for manufacturers to use the same PCM in a wide range of vehicles. They just "flash" it with vehicle-specific information and pop it in. There are "tuners" for just about every vehicle manufacturer these days that will flash your PCM for you in order to increase performance, eliminate emissions checks, etc. There are also DIY software packages that allow you to upload information to the PCM yourself. On my '96, for example, I tuned out the AIR pump check so the SES light would stop coming on once the pump failed. I also changed the temperature at which the fans come on so it ran cooler.

As an aside, our computers *might* have a CALPAK or MEMCAL chip in them. It is an actual chip that has default, limp-mode fueling information in the event the main computer fails. Not sure when GM stopped using those. I think that's what Autozone is showing you, actually. EDIT: I pried open an extra '96 PCM I have and it does not have any sort of removable chip in it other than the knock sensor module.

This guy has lots of information on LT1 and LS1 tuning: http://www.lt1pcmtuning.com/

Back to your issue: you can't really check the PCM for faults. You can send it to a tuner to see what's been changed vs. stock, but in order to do it yourself you'd have to invest in software and cabling. I doubt the PCM has failed. You can have it put back to stock, but if the previous owner has had it reprogrammed to eliminate certain emissions equipment, and has removed that equipment, then you're going to get a Service Engine Soon light when the stock programming looks for that stuff again.

I think you should be looking beyond the PCM for your issue, particularly if the program you have had been working fine in the past. Something has failed that is causing it to run poorly.
 
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