FiTech EFI Tuning Forum

Please or Register to create posts and topics.

Tach Signal missing

Page 1 of 4Next

Hi everyone, I am new here and I have a customer in my shop with a 1966 Bronco with the 400HP system installed. I did not do the install and this is my first time seeing this truck. It was towed in from the beach where it died while idling and would not restart. Found codes for RPM noise and have no tach signal. I confirmed the HEI distributor is working properly. Checked the wiring from the HEI to the Fitech ecu and found whoever installed it tapped into it for the external tach in the truck. I removed the external tach wire with no difference. I then talked to Fitech support after being on hold for 30 minutes and they said to isolate the wire and try tapping it to the positive terminal to see if you get readings on the handheld display. I isolated the wire and made sure it was completely away from everything all the way to the ECU. Still no readings at all. During all this I also confirmed the power to the ecu and getting 11.8 volts. Additionally I ran a new ground wire directly to the fuel injection unit with zero change. I am feeling that I have a cooked ecu but looking for other thoughts. Is the ecu common? still power ups and I get all the other readings. One more thing to note, when you cycle the key you get the fuel pump to run for a few seconds and the truck with fire a few times. Then nothing until you cycle the key again.

That gives me some direction.

When you crank does the screen go black?

Either low voltage and/or switched wire is not getting voltage during crank, thus turn the unit off.

The unit has a prime shot that squirts fuel when you cycle the key.  Since the ignition is still active, the motor will try to start with that small amount of prime fuel.  But, the Fitech is not seeing RPM so it never fires the injectors.

Make sure the unit is has a good switched source for crank.  "White wire".  If ok, make sure unit is staying on during crank.  These are very sensitive to voltage drops.

Yes stays on completely during crank (10.9 Volts I believe but can confirm) and when I just have the key on and I tap the blue tach wire to the battery positive (as Fitech support recommended) I get no movement in the rpm screen of the handheld.

 

 

Ecu do go bad from time to time.  Usually misuse or bad install, but it happens.  Fitech is pretty good about fixing or replacing.  Must have original receipt.

 

Ok thanks, I will send it off to them and let you know the outcome!

 

Deleted user has reacted to this post.
Deleted user

It is difficult for me and you when it is someone else's install.

Hi

I just installed the new 39001 2 barrel with a 40015 in tank pump on a rebuilt but standard 352 FE.

I am having significant start issues hot or cold, once running it is great.

I have reset to a base calibration, here are my observations.

  1. Once I have set the IAC to read between 3 and 10 when hot, the next time I start from cold the setting will change.
  2. The engine will fire and dies, no matter how much cranking fuel I add. The only way I can get the car to start is to switch the key on and off 3 or 4 times (without cranking) to engage the priming shot each time, and then it starts using the throttle while cranking.
  3. I have put in a relay on the white wire and now gets 10V + when cranking, I have also earthed the Fitech body to the battery, however I dont get any RPM displayed on the handset when cranking. Once running it displays fine. I am getting the tach signal from a street fire CDI, PN 5520 using the tach wire supplied. Im not using the Fitech to control ignition.

Can anyone suggest what I should try next?

 Im in New Zealand and dont particularly want to call Fitech support given the reputation they have for keeping you waiting.

 

Thanks Mark

Mark johnson

Here is what is happening.  The prime shots is giving you enough fuel to fire the engine.  When you let off the key the unit is seeing RPM and begins firing injectors and keeps it running.  I see this a lot when the white wire loses 12v during crank.  In your case, it seems the unit is staying on.  Your problem is rpm signal.   I would look at your trigger wire (blue).  The blue wire is very sensitive to electrical interference.  Try shielding.  Use shielded plug wires. Resistor plugs.  Make sure the blue wire is not near any other wire.  There is a shielding sticky in this section.

Thanks, I now have another project for the weekend.

 

Ill let you know how I get on.

Deleted user has reacted to this post.
Deleted user
Mark johnson

Also is it normal for the IAC setting to change between cold starts?

Mark johnson
Page 1 of 4Next