No Start Diagnosis Help

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No Start Diagnosis Help

Post by Themanytoys »

Hello everyone. Recently bought a '95 Beretta 3.1 and been trying to turn her over but no success.

Fuel pump and filter have been replaced - fuel pump pressure has been restored and pump gets power when key is "ON"

Coil packs have power. Spark plugs wires are good. Spark plugs are good. Spark at the turn of key is good so, I can assume that the timing chain is good.

Throttle body sensor have resistance.

So, it comes down to the Crankshaft and CAM sensors. This morning I sprayed starting fluid to see if she will stay on and it turns over and dies. So, I would assume that the PCM is cutting off fuel due to a faulty sensor.

I did a multimeter test using 20k ohms on the CAM sensor (only - disconnected from harness) to see the resistance - got a very quick flash of 19ohms then lost signal - reversed the multimeter plugs and got 13ohms steady.

Could this be my issue? Thoughts?

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Re: No Start Diagnosis Help

Post by Rettax3 »

IIRC, the '95 (and I have two of them, though one is no longer a 3100, with the bigger Quad-Cam 3.4 sibling from a '95 Z-34 shoe-horned in instead :twisted: ) 3100 will run with the cam sensor disconnected -it needs this for the Sequential function of the "SFI", and will revert to batch-fire without it -I could be wrong though, so with an anomalous reading, don't rule it out, it has been several years since this has come up for me. Try unplugging it altogether to see if that helps or hinders if you have no way of reading PCM data.

The spark is controlled by the Low-Res (7X) CKP (Crankshaft Position Sensor) at the rear of the block, directly into the ICM (Ignition Control Module). The PCM sends and receives data from the ICM to adjust spark timing off from 'base', but the ICM actually runs the coils directly itself. If the Low-Res sensor goes out, you will have neither spark nor fuel-injector pulse. Can you test the Injector pulse with a Noid-Light set? The third sensor to look out for is the High-Res (24X) CKP, behind the harmonic-balancer. The wires tend to get chewed-up by small debris thrown around by the pulley. If this sensor is bad, you will receive the symptoms you have described.

Other areas to look at though are:
-Faulty Fuel Injectors -I once bought a Third-Gen Camaro to help out a co-worker who needed cash and had to sell his car for cheap, and five of the six injectors (3.1 MPFI engine related to, but not the same as, your 3100) were bad. Either stuck open, stuck closed, or just a bad spray pattern that dribbled instead of atomized... Also similar symptoms, though that car had sat for a while. Did you perform a pressure leak-down test on your fuel system to see if either the FPR (Fuel Pressure Regulator) is faulty or an Injector is stuck open?
-Next, consider the condition of your fuel -there is a gas-station near me that is notorious for getting water contamination in their fuel storage-tanks... A customer of mine runs a local business, and asked me to diagnose a no-start condition for one of his delivery vehicles... After testing the vehicle, I found nothing wrong, but in testing the fuel, I found that even with a propane torch I could not get most of it to burn! He had 12 gallons of fresh gas pumped into his tank, that was actually about 86% water... Not sure how that "gas" station has remained open, but they still are.
-Perhaps more likely is the Fuel Pressure Regulator itself may be faulty... Even if your Fuel Pressure is running to specification (you didn't mention what PSI you were reading, but I will assume since you tested it, it is within range?), I have seen a couple of GM FPRs blow their internal diaphragm, and they start dumping raw fuel into the engine via the vacuum-control line. Again, similar symptoms to what you are experiencing.
-Also, since the car is new to you, consider if a previous owner has installed an aftermarket alarm system. Though more common to have only a start-inhibit function that would prevent cranking at all, it is possible some model alarm out there may emulate many of the factory alarms that cut-off the fuel-injectors after the initial prime. I can't recall EVER seeing one of the GM VATS or PASSLOCK 1 or 2 systems on a Beretta of ANY year, but that doesn't make it impossible. Three of my Berettas now have one or another of these active factory anti-theft systems in them, with another slated to get one at some point in the future when I finally get around to swapping in another 3800, and they also do the exact same thing you have described when they get tripped.
-And perhaps the worst scenario would be a plugged catalytic-converter. Sometimes they are easy to diagnose, but I got bitten very badly by a Chevy Celebrity with a 2.8 MPFI (again, very similar to your 3100 SFI engine) that had a plugged cat. The car had gone to multiple shops, virtually EVERY relevant component had been replaced all the way up to the ECM, and while I found several overlooked contributing issues along the way myself, such as a leaking EGR valve, it took another co-worker who had also encountered (and struggled with) a similar issue in the past to point me in the right direction... Try removing your O2 Sensor, and see if it will light-up and stay running at least at idle. Even that tiny hole can release enough exhaust back-pressure to let it run if the converter is plugged.
-Lastly, have you checked the MAP sensor? The vacuum Tee may be split, or it may be a bad sensor. If the PCM is getting a wonky signal, it will run the fuel mixture all over the place, and the car won't run right or likely not at all.
-Oops, okay last one now, how about the Coolant Temperature Sensor? A bad sensor in a GM of that era is like having a stuck choke -stuck open or stuck closed, depending on how the sensor has gone bad. If the CTS is out to lunch, your car may barely run, or not even start at all if the PCM is flooding it, thinking it is 40-degrees below zero (read default temp).

Good luck, keep us in the loop on what you find. Being an OBD 1.5, the '95 is the hardest to find a scan-tool that can connect to the PCM, but reading live PCM data is priceless in situations like this.

1989 SuperCharged 3800 Srs-II (First)Six-Speed GTU
1990 Turbo 3.4 5-Speed T-Type
1990 4.0L 4-Cam 32-Valve V-8 5-Speed Indy GTi (Project)
1990 Stock(!) 3.1 MPFI Auto Indy
1995 LA1/L82 4T60E Z-26
1995 3.4 DOHC Turbo 5-Speed Z-26
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