3.4 DOHC Swap Couple Questions (Page 2/2)
355Fiero JUL 25, 03:54 PM
Marc-Alan;

If you are running only the two wire from the lower intake Manifold, where do you get your temp gauge feed from? Do you splice into the temp wire which goes to C16 or do you get it from another location?

I got the three pin temp sender unit so I can still have C16 and C2 feeds stay on one circuit and I will run my temp gauge through C500 D3 or C2 (can't remember which) to the third pin which "should" give me the temp gauge feed I need without messing with the ECU feeds.

Also going to try to insert the speedo buffer into my speedo circuit as well to see if that gives me the speedo finally. The buffered output from the ECU did not work either. Also going to look at the speedo gauge again and make sure I am connecting everything correctly.....

More to come
Don
355Fiero AUG 03, 04:06 PM
OK this water temp gauge and sender is driving me crazy.

I bought a replacement three pin temp sender that cross references to the 3800 three pin that has been listed here and installed in the Lower Intake Man where the two pin was. I have ECU temp being read (confirmed by TunerPro), but it is only going up to about 160*F (70*ish C) max and pretty sure it is hotter than that. Of course with that, the fan is not turning on so I did not run it too long to ensure I did not overheat the engine. In the past attempts, I would have operating temp much faster than I was seeing today so I wonder if the sender has different ohms range than the oem two pin?

I also ran a new wire from the 3rd pin right to the C500 block D3 which then goes to the water temp gauge and I have confirmed continuity end to end. Still no joy on the water temp gauge itself either so I am also going to go get a new water temp gauge to see if my gauge is pooched. Wouldn't that be a ***** if that was the issue all along?.... I traced the C2 C500 block wire to the dash and to the single pin sender in the forward head as part of the swap harness. I used D3 which was empty for the coolant temp gauge

A quick question for the DOHC knowledgeable folks. I assumed the single pin sender in the forward heaad is the water hot or low coolant sensor listed in the 96 manual. Is that a correct assumption or is that a single pin water temp sensor? I find as the car warms up, the water warning light on my dash (Pisa not Fiero) that this sender is connected to starts to light up slowly.... I have the C2/forward head sender connected to my water temp warning light and the third pin (C) on the LIM sender to D3 and through into the temp gauge.

I do have oil pressure gauge now as I replaced the oil sender with the '88 Fiero sender so that is good but I also no longer have tach. It worked for a bit and then stopped on me. Going to do continuity checks on that wire again as well to make sure it is good end to end....

This dash wiring is killing me but I will know a WHOLE bunch about all of it by the time i am done......

Thoughts would be appreciated.

Thanks
Don
Rick Vanderpool AUG 03, 07:40 PM
Don, Did the VDO temp gauge come with a sender or do you have to calibrate it to the stock sender? The sender is a thermistor which changes resistance as the temperature changes, and the gauge and the sender have to match.
I am putting a 3.4 DOHC in a Formula I am making a GT40 out of. I am using Speedhut gauges and have done a lot of research on how to wire them. The 1 wire sensor in the front head is the source of the signal for the temp gauge in the W body car the engine came in. The two wire sensor in the intake manifold only supplies signal to the ECM. For the Speedhut gauge there was a new sender thermistor which replaces the stock sender in the front head.
Rick
olejoedad AUG 04, 12:28 AM
The temp gage is C500 C2.

The HOT lamp is C500 D3.

Edit:

I see your modified your harness circuit assignments.

The above info is for OEM wiring.

[This message has been edited by olejoedad (edited 08-04-2022).]

355Fiero AUG 05, 10:55 AM

quote
Originally posted by Rick Vanderpool:

Don, Did the VDO temp gauge come with a sender or do you have to calibrate it to the stock sender? The sender is a thermistor which changes resistance as the temperature changes, and the gauge and the sender have to match.
I am putting a 3.4 DOHC in a Formula I am making a GT40 out of. I am using Speedhut gauges and have done a lot of research on how to wire them. The 1 wire sensor in the front head is the source of the signal for the temp gauge in the W body car the engine came in. The two wire sensor in the intake manifold only supplies signal to the ECM. For the Speedhut gauge there was a new sender thermistor which replaces the stock sender in the front head.
Rick



Thanks Rick;

From what I have been able to figure out, the sensor in the front head on my engine is a switch only and not sensor as these cars came with different sensors depending on the options that were installed in the car at factory. Warning light only or temp gauge etc. My engine is a crate engine so no idea what vehicle it would be in so not sure what the sensor is. I do know hooking it to the VDO temp gauge does nothing so I am going to order in a VDO sender.

Now for everyone, do you know what the thread is for the front head? is is 1/8" NPT or 10 mm straight? I have to think 1/8" NPT?

Thanks for all the help folks. I think I have been overthinking this issue a bit and caused myself delays I probably did not need to......
Don
355Fiero AUG 05, 10:59 AM

quote
Originally posted by olejoedad:

The temp gage is C500 C2.

The HOT lamp is C500 D3.

Edit:

I see your modified your harness circuit assignments.

The above info is for OEM wiring.





Thanks Joe and yes, I think I overdid the complicated part on this..... The harness had the wire running through the C2 connection but I used that for the warning light and front head switch. Now I am gong to go back and use that C2 connection as the water temp sender and not have a water temp warning light. Ryan at Sinister said I could use the Fan 2 output as the warning light feed as it is not used on the Fiero and it is set high enough to be a useful indicator.

Cheers again all
Rick Vanderpool AUG 05, 11:48 AM

quote
Originally posted by 355Fiero:

Now for everyone, do you know what the thread is for the front head? is is 1/8" NPT or 10 mm straight? I have to think 1/8" NPT?




It's 1/4 NPT
355Fiero AUG 05, 06:47 PM

quote
Originally posted by Rick Vanderpool:


It's 1/4 NPT



Prefect thanks Rick. Ordered so hopefully this particular adventure is all over in a few more days....

Cheers
Don
355Fiero AUG 07, 03:35 PM
Figured I would update here and give more search capability for folks looking at aftermarket gauges for the Fiero.

Speedometer. I had to reset the VDO speedo to 4000 ppm as for some reason it went back to factory. Speedo works fine now. I pulled the buffered speed output from the ECU and confirmed the Speedo was set for 4000 ppm. If you take it straight off the VSS yellow wire, you will need to add in a buffer circuit per other posts across the forum.

Tachometer. A VERY easy fix once I found it. Put a 1 kohm 1/4 watt resister between the 12v power pin and the tach signal wire on the back of the tach gauge and it acts as a power pull up and strengthens the signal. The coil pack on the 3.4 and 3800's apparently do not have enough juice to power the gauge. Easy fix

Oil pressure. Swapped in the 3 pin '88 oil pressure sender per The Ogre's page and works fine now

Water temp. I have a single pin VDO sensor coming that will replace the water level sensor in the front head of the 3.4. I just won't have a water warning light.

All sorted and on to al the other stuff now to get this thing done and on the road for good.
Cheers
Don

Pull up resister image I found on the LS1 forum talking about the tachissue.

[This message has been edited by 355Fiero (edited 08-07-2022).]