2G Hard starting and CAS over voltage

[TC1995]

Summary
1995 GSX manual abandoned 18yrs.
Have gotten it intermittently to start and idle even briefly move into the driveway under it's own power

Full background and build thread if desired (https://www.dsmtuners.com/threads/9...-recommendations.549900/page-3#post-153969965)

I'm having difficulty easily getting it started and maintaining idle, once it does I'm starting to suspect that something is telling the car not to send fuel spark etc. Might be unrelated, but when the car does idle, pushing throttle down is very sluggish and basically gave very little response.

I'm going to change out fuel filter to ensure no restrictions under higher load but with the fuel that dumps out when I tested my new fuel pump at the rail I highly doubt I have fuel issues at idle and on startup. I did just get in a fuel pressure gauge test kit to confirm either way eventually.

Starter is cranking motor just fine at good speed

Battery always charged when I test as I keep a low amp tender on between working on it.
I narrowed down my thoughts to the Camshaft sensor up top near the intake.

Thought process was if it's getting dirty or bad signal about camshaft etc car goes into limp mode and makes starting very difficult and very resistant to reving once it does.

To test the sensor, not only did I have to remove the headlight, motor mount and timing cover but apparently only Jesus is getting to that camshaft sensor behind the intake cam gear cause no way I'm getting that . So switching gears to testing electrically through the connectors.

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Oddly enough when probing my multimeter into the harness for the signal wire and the incoming 12v power with the key turned on I'm getting ~7.4v which is odd. If anything, I think the pull down resistance voltage should be 5v and go to zero when sensing the cam. So I then connected the sensor back up and left probes in and instead when operating/cranking motor I'm getting between ~6v-8.5v. I know signal wire is square waveform so not best to use multimeter for checking signal pulse (I don't have a noid light) but either way it's not at all the voltages I expected.

Ironically enough I think it might point to wiring short or break instead of bad sensor which would be easier to fix, I think, but still quite confusing. Thinking about wiring up a speaker with resistor to listen to pitch of the signal and do quick check if it's at least increasing when engine cranks and rpm goes up. (Or if I can get it started and rev it listen to signal). But open to ideas as to what might be the issue.

My next steps are to confirm good continuity and clean ground at the harness side plug, might also check timing on the off chance somewhere along the line skipped a tooth or something dumb. (doubt this though since when it idled sounded good smooth and all four cylinders were firing I have some videos in the thread of it running)

 

[steve]

If in fact you're seeing 7.4v on the cam sensor signal line, I'd check some of the other signals that have 5v pullups from the ECU.
While cranking battery voltage usually drops quite a bit from the current the starter draws but you should still only see ~5v on the signal pullups since they are from the ECU's +5v voltage regulator.

 

[TC1995]

If in fact you're seeing 7.4v on the cam sensor signal line, I'd check some of the other signals that have 5v pullups from the ECU.
While cranking battery voltage usually drops quite a bit from the current the starter draws but you should still only see ~5v on the signal pullups since they are from the ECU's +5v voltage regulator.

I'm assuming other easy systems to check that refernce voltage would be the Crankshaft Position Sensor (CKP) — same Hall-effect style as CAS right in same spot I already have pulled apart, same 5V pullup circuit. Hopefully to help tell me if I might be dealing with bad ground, short etc somewhere?

 

[TC1995]

""""If in fact you're seeing 7.4v""""

"IF" was the key word here, thank you !!

I went back to test this today with fresh brain rather than the potato brain of last night.

Oddly enough when probing my multimeter into the harness for the signal wire and the incoming 12v power with the key turned on I'm getting ~7.4v which is odd.

I was checking reference for my voltage, against incoming 12v, instead of ground. So yeah 12v - 5v = 7v.
Checked a few other sensors like crankshaft as well to confirm but exactly ~5v on the signal wire when key is on, so at least we know incoming conditions are normal.

I will reconnect sensor to harness and try to crank again with crude multimeter test (properly probed this time) to see what type of action we're getting roughly, but I'm thinking the sensor is likely ok? Going to see if I can track down proper tools so I don't have to try and remove the sensor cause seems not worth the effort with it behind that intake cam gear.

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I started to look at some other potential causes and relays, took center console apart and found my main starter relay behind the dash is just jumped right now (so assuming the relay present is toast) I have another ordered that I will throw in once I test it.

And realized as well that the clutch pedal switch is either broken or intentionally jumped (I would assume they did it for crankwalk reasons?)

 

[TC1995]

Still having trouble with getting car to start reliably.

I now have two starter relay and both are working just fine when bench testing. I probed the back of the connector when cranking and the voltage is very inconsistent unless the connector is jumped it won't even activate the relay and car will simply not crank. Some context the driver window was smashed and open to the elements for several years before I bought it. So currently I'm thinking something along the lines of corrosion of the contacts for ignition cylinder/circuit loop? Unless someone has another suggestion, Also tried hitching up fuel pressure tester off the fuel filter and getting no pressure so something is cutting signal to the pump, cause if I power the connector under the hood against the firewall it pumps fuel fine (I just did a wal255 upgrade since pump was busted when I bought car) yes could be that oring not seated properly in the hanger (I will need to test pressure under that condition to be sure but given I pumped several gallons out at the rail after install to purge the tank I'm not thinking that's the issue) with the signal issues I'm seeing at the starter relay I think I'm going to pursue the electrical cause first

 

[We're on Boost]

took center console apart and found my main starter relay behind the dash is just jumped right now (so assuming the relay present is toast) I have another ordered that I will throw in once I test it.

And realized as well that the clutch pedal switch is either broken or intentionally jumped (I would assume they did it for crankwalk reasons?)

I now have two starter relay and both are working just fine when bench testing. I probed the back of the connector when cranking and the voltage is very inconsistent unless the connector is jumped it won't even activate the relay and car will simply not crank.

I would continue to use a jumper instead of the starter relay. The starter relay doesn't do anything to reduce the current through the Start leg of the ignition switch. All the current through the switch side of the relay comes from the ignition switch. So you might as well jumper it.
Also with the clutch switch, leave it disabled for the sake of your crankshaft thrust bearing.
"When bench testing" - reminded me that my starter relay tested ok after I took it out. But for some reason my cranking was more reliable with the jumper. Eventually I replaced that entire Start circuit from battery to starter solenoid with new 10ga wire and a 50 amp momentary push switch, to simplify, and so that none of that current would be going through the ignition switch. But I did have to add a connection back to the original circuit to continue activating my "KeyStart" function which you need for Cranking Fuel Adjust.

Here's what I have for circuit diagrams to show how the starter relay is in there.
You can see that for years 91-97 the only model that used the starter relay to take load off of the ignition switch was the 2.0 liter non-turbo with automatic trans. On all the other models, the starter relay got its big current from the Start leg of the ignition switch.

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