3.8 not cranking & fuel will only prime

Old 07-10-2019, 10:13 PM
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Default 3.8 not cranking & fuel will only prime

So we have this mid 90's something camaro with a 3800 engine and manual trans..

Flicking the key primes the fuel for a couple seconds..Key crank position does not crank..

Found the fat purple wire for that starter solenoid and hit it with +12V.. Engine will start on the prime but looses fuel pressure.. Can keep engine running by flipping the key back and forth to make it prime up over and over again..

I am about to just put switches to the starter solenoid wire and a switch for the fuel pump but maybe their is some common solution to this elctronic problem that you know of? Do you have any idea why this car won't crank or run the fuel pump if I crank it by bypassing the cranking circuit?

It makes me think that the ECU is not seeing RPM to run the pump or some stupid safety thing is not letting it run..
I imagine you should be able to bump start this car so something must be keeping it from cranking and running the fuel pump through its usual circuits..

It looks like the clutch safety switch is taken off and we tried that both jumped and open to see if that would work and no..
Looking at both fuse blocks under the hood and inside by the steering wheel I can't find anything fuel pump related..

This car is somewhat solid bodie, and has low miles, and we got it for a stupid good price, and I got it to start n like half an hour of finding wires so I feel pretty accomplished for that feat alone.. Not too bad for a shadetree hickerbilly..
I think it would rip with 2 switches for the fuel pump and starter but it may be easier than that if this is some common idiotproofing malfunction if you know what I mean..

The turn signals also do not work.. But I think most everything else does..
Old 07-10-2019, 11:33 PM
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The car is equipped with a theft protection module and theft deterrent relay that controls the starter and the fuel pump. The theft protection module controls the theft deterrent relay coil to energize, which closes the relay contacts to allow the starter to run and it also controls the PCM fuel enable circuit. To activate the theft protection module, the module has to receive a resistance value from the key switch that matches the value stored in theft protection module. Because neither the starter or the fuel pump is working, the chances are good the theft protection module is not allowing the starter and fuel pump to energize. The first thing I would check would be if the key switch contacts are able to read the key chip. You should be able to disconnect the two wire key switch wiring connector at the base of the column and use a meter to read the resistive value of the key in the switch if the contacts are good. When you provide 12V to the purple wire going the starter solenoid, you basically by passing the theft deterrent relay and repeatedly cycling the key allows the fuel pump to re-prime but not pump enough fuel to maintain operation. I've attached a drawing showing the Vats and Theft Protection Module and Theft Deterrent relay wiring.

The clutch switch will also need to be working correctly or by-passed for the starter to engage with the key switch.
Attached Files

Last edited by peterpar; 07-10-2019 at 11:44 PM.
Old 07-12-2019, 11:32 AM
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Join Date: Jul 2019
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Thanks for the most excellent reply!
But he took the car to some guy with a magic diagnostic computer and I guess they worked on it all day yesterday and still haven't figured it out.. They said something about they don't get 5 volts out of the security box where it should be and that even after jumping the fuel and starter it is cutting ignition too..

IDK what's going on really, he took it to someone else but I might end up trying again if the guy gives up..
Old 07-12-2019, 12:29 PM
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Originally Posted by FastEddie313 View Post
They said something about they don't get 5 volts out of the security box where it should be and that even after jumping the fuel and starter it is cutting ignition too..
Not sure what you're referring to as a security box, so I'm assuming you are talking about the Theft Protection Module. The module provides a path to ground for the Theft Deterrent Relay coil to energize the starter and a ground input to the PCM to enable the fuel pump. I believe the key switch circuit is also a path to ground for the I/O resistor who's signal enables the Theft Protection Module, so I don't understand what 5 volt source they don't have. I've attached pages from the 1995 service manual that may help explain how the Theft Protection system operates.

Again, the easy way to check if this condition is the cause of your problem is to check the connector at the bottom of the column with a ohm meter to see if the key chip resistor can be read. If the value is the same as the checking the key out of the switch, then it is not your problem. In other words, if the key chip is a 15 ohm resistor, the reading should be 15 ohms or close reading at the connector.
Attached Files
File Type: pdf

Last edited by peterpar; 07-12-2019 at 12:49 PM.
Old Yesterday, 10:26 AM
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These PDFs worked for a while but now "you do not have permission to access this page."


Well I guess they work in another browser that I'm not logged in from..
Old Yesterday, 10:56 AM
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Still working here, Check your download folder. This one seems to auto download.
Old Today, 04:01 PM
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may need a couple more posts. new members have limited access to discourage spammers posting. need at least 3 if memory serves, may need one or two more.
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