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| 4.9L Intermittent PCM issue (Page 2/3) |
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87GTBrad
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JAN 31, 12:51 PM
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Thanks Sanderson 231, I have done exactly that vss goes to the dash direct and the speedo is working, I read online that in order for the engine to run correctly it needed the vss feed back (this was a Fiero Factory 4.9 conversion post). My car is idling ok but running really rich stinks of unburned fuel. This is why I'm looking for someone that has experience with this swap to check out my current program for errors that maybe causing my drivebility issues. Any help is appreciated. This is not a race car and I have no intentions of modifying the engine further, Just looking to get it running correctly. 200 hp should be plenty. Also a shout out to member Mickey_Moose who's posts were invaluable to me going it this far 
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Raydar
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JAN 31, 01:55 PM
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| quote | Originally posted by 87GTBrad:
Thanks Sanderson 231, I have done exactly that vss goes to the dash direct and the speedo is working, I read online that in order for the engine to run correctly it needed the vss feed back (this was a Fiero Factory 4.9 conversion post). My car is idling ok but running really rich stinks of unburned fuel. |
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The PCM needs to be "faked out" by grounding a couple of the auto trans wires, to make it think it's in Drive. I don't remember which two wires, but I can dig it up if I need to.
Since the Caddy never came with a manual, it's hard to figure out what to tweak. I bumped up the idle speed a bit, and did a few other things, but nothing I can point to.
The 4.9 is difficult to tune because there are at least FIVE different files that could be used to tune, depending upon which year and model the donor was. You have to use the correct one, or the data will be nonsense.
But about the rich running... Make sure that your O2 sensor is good. They can fail, indicating "full lean", which will cause the PCM to dump fuel in. It can even kill your catalytic converter, if you have one. (Don't ask how I know this.) You can test it by unplugging it, and then resetting the PCM by disconnecting the battery. The engine will run on pre-programmed, default values. If the rich condition goes away, you've probably found your culprit.
I used an NTK replacement part. (Advance Auto is where I found mine.)
Also, if you have a scan tool, you should make sure that the PCM is seeing the correct values for coolant and air temperature. If they're reading very cold, it will also cause rich running.
Third... make sure the power steering input on the PCM is jumpered. If not, that can also cause it to run rich.
Regarding the wiring, if you got your info from Mickey Moose, everything I suggested checking is probably already accounted for.
There are a couple other "gotchas" that happen if you're using an Allante intake manifold. Since you didn't mention that, I'll assume that you are not.[This message has been edited by Raydar (edited 01-31-2023).]
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87GTBrad
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JAN 31, 03:13 PM
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Thanks for that Raydar. I pretty much used Mickey Mooses wire post as the schematic for my build grounding as described also installed the security chip defeat device. O2 Sensor is new but I will try what you have suggested and see what happens. Unfortunately the company I sent my chip to changed out the stock fuel map for one they said was more suited the Manual trans. Any idea if that fellow "Rockcrawl" is still programing? All the posts I have see him mentioned are years old. I will open up the ecm and see what numbers are on the chip and get back to you in a bit, unless it turns out that the O2 sensor is the culprit then the problem will be solved. thanks again.
Brad
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sanderson231
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JAN 31, 05:55 PM
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To diagnose the rich condition you really need to get a scan tool on it or datalog with a laptop (free software is available). The short term fuel trim (aka integrator) should be bouncing around 128 with a stock tune if everything is right. If it is reading low the O2 sensor is seeing a rich condition and it is biasing down the fuel injectors to try to correct the rich condition. But the integrator can only adjust so far and if it is bottomed out the engine will run rich. Of course your chip is not stock and whoever messed with the tune may have created the rich condtition.
I have seen a lot of plugged 4.9L fuel injectors. If the engine has sat around, I recommend pulling the fuel injectors and having them professionally cleaned. Mr Fuel Injector in Idaho does it for $18 each. A partially plugged fuel injector can cause a rich condition. One cylinder runs lean and pumps excess O2 into the exhaust and then the PCM makes the other cylinders run rich to try to get back on ratio.
As I recall Mickey_Moose wires the cars as a 1992 Deville. In 1992 a 16132240 PCM was used. From what Tunercat has on his website, a 1994 uses a 19196347 PCM. There may be some wiring differences. The 16196347 may not be entirely compatible with 1992 wiring. Please tell us what PCM you have (label on outside of the box) and what broadcast code the EPROM is (four letter code such as BWYZ on the EPRM itself).
I was thinking that it might be necessary to adjust the decel enleanment and decel fuel cut-off parameters in the PCM for a manual transmission. I see no reason to mess with other parameters that effect the fuel trim.
I can burn a new electrically erasable EEPROM. You would have to buy an adapter to install this. I do not have a UV eraser to modfiy your old chip.
Raydar, I checked my 1992 Deville factory service manual. From what I see in order for the PCM to think the transmission is in drive, the following is necessary:
PCM wire F8 needs to see an open
PCM wire C10 needs to be be grounded
PCM wire F7 needs to be grounded
PCM wire A2 needs to see an open
Thanks for bringing this up. I'm putting the final touches on a 4.9L manual for a friend and I'm sure he missed this.------------------
formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged
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Raydar
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JAN 31, 07:39 PM
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| quote | Originally posted by sanderson231:
To diagnose the rich condition you really need to get a scan tool on it or datalog with a laptop (free software is available). The short term fuel trim (aka integrator) should be bouncing around 128 with a stock tune if everything is right. If it is reading low the O2 sensor is seeing a rich condition and it is biasing down the fuel injectors to try to correct the rich condition. But the integrator can only adjust so far and if it is bottomed out the engine will run rich. Of course your chip is not stock and whoever messed with the tune may have created the rich condtition.
I have seen a lot of plugged 4.9L fuel injectors. If the engine has sat around, I recommend pulling the fuel injectors and having them professionally cleaned. Mr Fuel Injector in Idaho does it for $18 each. A partially plugged fuel injector can cause a rich condition. One cylinder runs lean and pumps excess O2 into the exhaust and then the PCM makes the other cylinders run rich to try to get back on ratio.
As I recall Mickey_Moose wires the cars as a 1992 Deville. In 1992 a 16132240 PCM was used.
Raydar, I checked my 1992 Deville factory service manual. From what I see in order for the PCM to think the transmission is in drive, the following is necessary:
PCM wire F8 needs to see an open
PCM wire C10 needs to be be grounded
PCM wire F7 needs to be grounded
PCM wire A2 needs to see an open
Thanks for bringing this up. I'm putting the final touches on a 4.9L manual for a friend and I'm sure he missed this.
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My Donor was a 1991 Deville. My PCM was also a 2240. I believe that most years/applications were 2240s.
"C10 and F7 grounded" sounds strangely familiar. Possibly the same as mine.
Injectors... yeah. From the time mine was swapped in by the folks in Huntsville  it had a bit of a skip to it.
I finally replaced my injectors with the orange Bosch Type III injectors. The skip went away.
Fuel Injector Connection (FIC) has them.
https://fuelinjectorconnect...-iii-design-set-of-8
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Mickey_Moose
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FEB 10, 04:54 PM
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| quote | Originally posted by sanderson231:
As I recall Mickey_Moose wires the cars as a 1992 Deville. In 1992 a 16132240 PCM was used. From what Tunercat has on his website, a 1994 uses a 19196347 PCM. There may be some wiring differences. The 16196347 may not be entirely compatible with 1992 wiring. Please tell us what PCM you have (label on outside of the box) and what broadcast code the EPROM is (four letter code such as BWYZ on the EPRM itself).
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What he said - it has been a long time since I did this, but I do recall there was something with the 94 PCM that it was not a good choice to use at the time.
I might still have the files for the EPROM, but again this would only be for the 1992 PCM
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Mickey_Moose
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FEB 11, 09:08 AM
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Ok, files have been uploaded here: https://drive.google.com/dr...Pxgyb?usp=share_link
They are in the \EPROM files\4.9l directory. Sorry I don't remember the specifics of the files other than the names that there are called. But includes both Rockcrawl and Stickpony images - you will have to load them into Tunercat and verify if the VATS has been disabled as I don't recall which had.
Stickpony was the go to person after Rockcrawl seemingly left the Fiero scene.
These are for the 2240 PCM (pre-94).[This message has been edited by Mickey_Moose (edited 02-11-2023).]
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sanderson231
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FEB 11, 11:16 AM
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I took a quick peak at the Rockcrawl and Stickypony calibrations. They both changed the pulses per mile for the VSS to 3975. The stock 4.9 BBXF calibration has 23754 pulses per mile. The VSS for the 4.9 outputs a square wave. The Fiero VSS outputs a sine wave of ~4000 pulse per mile. Despite the different wave forms this implies that the Fiero VSS can be wired to the 4.9 PCM if the speed pulses per mile is changed to 3975. But the 4000 pulse per mile square wave output from the 4.9 PCM would need to be converted to a 4000 pulse per mile sine wave to make it compatible with the Fiero speedometer. The circuitry to make this conversion consists of two resistors and one capacitor which is easily incorporated into the wiring harness under the console.
There were some small changes in the spark advance tables in the Rockcrawl and Stickpony calibrations. There were no significant changes that would effect air fuel ratio. ------------------
formerly known as sanderson
1984 Quad 4
1886 SE 2.8L
1988 4.9L Cadillac
1988 3800 Supercharged
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Mickey_Moose
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FEB 13, 05:42 PM
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| quote | Originally posted by sanderson231:
But the 4000 pulse per mile square wave output from the 4.9 PCM would need to be converted to a 4000 pulse per mile sine wave to make it compatible with the Fiero speedometer. The circuitry to make this conversion consists of two resistors and one capacitor which is easily incorporated into the wiring harness under the console.
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Yes, you can direct drive the Fiero speedo with this change (that is what I did) - the circuit for the conversion is also listed in my build thread: https://www.fiero.nl/forum/Forum2/HTML/098096.html
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Mickey_Moose
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FEB 13, 05:44 PM
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I should add, that the pulses per mile in those file are with stock tire sizes (stock 15" wheels). This number will vary depending on the tire size. 
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