1G Factory tach drops out at 4500 rpm

[jbouvier]

Alright I just bought my 1g about a week ago, and have had to fix a couple things. Im on the last one...... The problem: whenever i get on the car and take it to above 4500 rpms the tach will hit the 4500 line and drop back down and wont come back up until I shift and the it repeats this action. Is this a problem with the wiring, or am I going to be out money having to buy an aftermarket?

James

 

[steve]

90 cars are known to have tach problems when a 91+ ECU is used.
Check the part numbers off the ECU and see if it's the correct one. You should have a MD145903 but a MD128625 will also be ok. Since people often swap parts around the board inside the case may be different. There should be numbers printed on the white connector on the ECU board. They should match the last 4 digits of the number starting with E2T on the top cover.

Steve

 

[jbouvier]

I know that the computer is a 1991 computer, I dont know the exact digits and the car is getting detailed so I guess I'll check that out when I pick it up later. So if the numbers match what would the problem then be? And if they don't I take it that I need to get another board or ecu from a 90? I had a friend of mine look at a turbo timer that came with the car for me and while plugging it into the harness around the pedal area he saw the computer behind where the radio goes, its not mounted where its supposed to be its just sitting there, and said it was the one out of a 91. These numbers were found on the outer case, and also said that it was probably chipped or something done being as the car runs fine and no idle problems or anything that would clue to something being out of the ordinary. If that was an accurate assumption could that be the problem? I seldom take it above 2500 RPMs its just when I do go above it, it bothers me seeing something not working correctly, not to mention not knowing what the engine is really reving at.

Thanks
James

 

[steve]

I know that the computer is a 1991 computer.

90 cars are known to have tach problems when a 91+ ECU is used.

If it is a 91 ECU then you either need to get a 90 ECU or figure out how much else has been changed in the car to see if you can just switch over to the 91+ power transistor module and feed the ECU from it's tach signal while leaving the gauge running off the stock 90 wiring.

What's the point of owning a DSM is you never rev the engine over 2500 RPM. The boost hasn't even started yet.

Steve