After starting up the car for the first time after the swap, which was pure bliss by the way, I realized that the oil gauge isn't working. The pointer goes to the maximum value as soon as the engine is running. Here is what I think is going on:

The 3800 is from a 2004 impala ss. I think this engine has a on/off pressure sender unit, and not a 0-90ohm sender unit. The fiero gauge wants to read a certain resistance, but when the 2004 sensor senses pressure, it opens. Which is equivalent to "infinity ohms". The gauge, not used to seeing anything more than 90 ohms, freaks out, and crams the needle all the way over.

My solution is to swap in a 0-90ohm sensor that will screw right in and replace the old pressure sensor unit. I know there are people with 3800's that have their oil gauges working, so speak up! I'm just curious if there is a drop in replacement oil pressure sender that will work with the fiero gauge. Or if everyone ended up monkeying around with their old fiero's pressure sensor to fit it into the 3800. A drop in replacement would be much preferred because I'm not so sure the original oil pressure sender worked too well :/.

If there is something that I'm missing, please let me know! Thanks in advance.

-Matt

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1987 Fiero GT. 3800 SC II engine swap in progress!

i used the stock fiero sending unit. All it does is run the guage and FP relay back up in my setup.

[This message has been edited by Jncomutt (edited 08-02-2007).]

On the three engine swaps that I have worked on, I used the Fiero's oil sending unit.
BTW, welcome to the forum!

Don Z.

Ditto on the Fiero pressure sender, however I pitched the one for the 86 out and bought the smaller, more acccurate 88 sender. The one for the 88 does not bounce as much and since it is smaller in diameter, was easier to fit in the space I had for it.

edit - the connector for the 88 sender is different than the one for earlier years, so if your car is not an 88 and you decide to go that route, you will have to get the right connector in addition to the sender

[This message has been edited by topcat (edited 08-02-2007).]

Just a note the SC3800 runs about 80 PSI normally. After the oil is warmed up it will idle about 40 PSI

I use the 88 Fiero ones on all my swaps it works just fine and is easy to come by at parts stores. Dan

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Signature compliments of F-I-E-R-O
2003 3800SC series II powered
www.photosled.com/showgallery.php/cat/631
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thanks for all the information!

Is there any drop in replacement 0-90 ohm sender that will fit that plug? perhaps one from a grand am or earlier 3800?

I don't care about the switching portion of it, I'm just relying on the ECM to control the fuel pump for now. I don't care about the backup oil pressure sender switch to keep it on. All need is the gauge portion I don't care to monkey with the old fiero pressure senders if i don't have to. (i'd have to find a new plug for it and everything :/)

-matt

The answer will depend on the type of sensor used. Those 3800SC's Grand Prixs that came with an oil presure sensor routed to a gauge will work, those that just powered a light did not. However, lack of pressure on the oil pressure switch should close the circuit and not the other way around. You might also encounter a three wire coolant temperature sensor whereas most 3800SC use a two wire sensor. Best that I can figure out the black and yellow wires provide the temp sensor output while the extra green wire on some of ther 3800's is probably a switch connection to the engine overheating/warning lamp.

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87GT 3.4 Turbo- 0-60 5.2 seconds
2006 3800SC Series III swap in progress
Engine Controls, PCM goodies,
re-programming & odd electronics stuff
" I'M ON THE LOOSE WITHOUT THE JUICE "