has spark wont start

i have an 03 gt, recently got it, replaced leaking coolant elbows. runs great. however i is ignorant when it wants to start. sometimes it fires right up, others it wont start regardless of how long you crank. leave it alone for awhile chances are it may start. i replaced the camshaft sensor, cleaned the tb and maf. and the check engine light went away. car started up multiple times for 1 day perfect, now im back to it not starting. i checked for spark, its there. it has fuel pressure at the rail. im stumped. the trac off light has always been on too, wonder if the crank sensor is bad? but you'd think it wouldnt spark if that was the case.

It's always, spark, fuel, compression? Has to be checked when it WON'T start....

Spark on all cylinders, using a spark tester?

Fuel pressure with a gage? Just depressing the schraeder valve is not a true indicator....

When it won't start, and you have spark, what happens when you spray cab cleaner into the intake? Does it start and run as long as you spray?

You say CE light was on....what was the code?

Since it intermittantly doesn't start, we can rule out compression....you either have it or you don't....

Also check vac line to f/p regulator for fuel and if it won't start, disconnect the MAF and then try to start it....

It wasn't starting last night, still had spark. And like i said; tonight after I get home from work I'll try and start it and it probably will. Then I'll shut it off and it probably won't start again. I sprayed it with starting Fluid and it fire for a sec bit then nothing. The ce is back on and I'll check the code tonight. The first time it sai camshaft error 0341 or something. But when it does start it runs like a top. It just starts only when it wants to. I pulled bac to fpr no leakage: disconnected Maf no difference

Didn't start tonight, fired up an fluttered for a second. Then just cranked. I replaced the fuel pressure reg tonight. Made no difference. Sprayed some fluid in intake and it started for a second. The pressure at the Schrader valve with the key on seemed weak when I depressed it. Think it's the fuel pump that's bad?

I don't like using starter fluid...a little dangerous....

I prefer carb cleaner.....need a second person to crank vehicle while you spray carb cleaner into the intake when it won't start....if it runs as long as you spray, either low on fuel pressure, or the injectors are not firing(if you have good spark on all six cylinders).....like I said before, you need to put a gage on that schraeder valve.....should be around/above 40psi....

Alright I'll put a guage on it tonight, I had one on it few days ago. When it was running it was 45 psi, but engine off and key on it int read anything, but there was pressure at valve bc it sprayed out when I released it. I thought the guage was bad. I'll also check for injector pulse. Could a bad crank sensor prevent injectors from firing? I'm still somewhat convinced its bad just because the trac off light is constantly on and is not related to abs

You say you have fuel pressure, but is the fuel pump priming every time? Can you hear it prime while you turn the key to the run position?

How about it priming it 4-5 times before you actually start it. If it starts, you know for sure it's a fuel pressure problem. If you can't hear the pump priming, then inspect the relays at the fuse block under the hood.

Oscar.

Could a bad crank sensor prevent injectors from firing? I'm still somewhat convinced its bad just because the trac off light is constantly on and is not related to abs

Crankshaft position sensor has nothing to do with ABS or Traction control; these are triggered only by bad ABS sensors (mounted at each wheel hub) or a bad ABS module.

Oscar.

Found out today there's no injector pulse.

If spark is OK then the crankshaft position sensor is OK.

Fuel injectors are triggered by the camshaft position sensor under the water pump. One more thing I would check is to disconnect the TPS sensor and try to crank the engine.

If it starts with the TPS disconnected, then you've found your problem. A bad reading will make the PCM "think" the gas pedal is all the way to the floor and will keep the injectors from firing (clear flooded engine).

Oscar.

It has spark. I replaced camshaft sensor last Saturday and it was running great all day. Sunday back to no start crap. I replaced it because it came up camshaft error 0341 I believe on scanner

In that case you might have a bad out of the box sensor. Inspect the wiring to make sure everything is OK.

I would do the TPS test just in case and check for 12v between each terminal at every injector plug and ground at KOEO.

I think that if you disconnect the camshaft sensor and try to run the car it would run as well; that will definitely confirm if your problem is the sensor (or wiring) or not.

Oscar.

Disconnected tps no luck. Same as Maf. Noid light tested the injectors no power. Checked the wiring to crank and cam sensor they looked ok. I'll try to disconnect the cam but I'm not very optimistic at this point.

Bad cam sensor won't prevent an injector from firing.......what will happen is the computer has to guess the correct time to fire the injectors.....there is a one chance in six, that the injectors will fire at the correct time.....won't prevent the engine from starting, but it could feel rough because they are not firing at the correct time......cam code can be caused by the sensor....can also be caused by a missing magnet on cam, bad harness connection to sensor/ICM/PCM, bad harness wire, bad ICM, bad PCM, etc.


this is a 3.8, correct? After replacing the cam sensor, were all codes cleared? Which codes returned? Were body, or "B" codes checked or just "P", or PCM codes?

If the injector doesn't fire, take a look at the SECURITY light.......there are two starter schematics to the starter, one uses the BCM, another doesn't.....

When you go to start the car, just turn the key to on.....don't crank.....look at the SECURITY light......it should go out after 3-5 seconds......if it does, attempt to start the vehicle....if it cranks but doesn't start, and there is no injector pulse, you need to check if there is a fuel enable signal being sent to the PCM(need a scan tool capable of reading BCM and PCM data).....

If the SECURITY light doesn't go out, and it cranks and doesn't run, then you know you have a THEFT DETERRANT problem.....

Like I said, your problem may be that you are not having BCM codes being read....average scanner can't read BCM codes.....

When I bought it she said someone the prior owner it needed a fuel regulator, I had the codes read, 0341 camshaft error and 0440 evap malfunction. I replaced cam sensor, cleared codes started up. Started not starting again that afternoon, I had some issues with the key so I ripped out the latch solenoid under the column ad it seemed to have fixed it, as it started numerous times after that. Next morning no starting again. Ce light came back on and the evap is back.

I'll check security later today

I think we should go back to the basics on this one. What are you missing at your injector pulse? Power or ground? Keep in mind the PCM controls the ground side of each injector individually. All of them share the power side which is I believe a pink wire if my memory serves me correctly. Said common (pink?) wire should show battery voltage anytime the key is in the on position.

As said by Tech II a faulty cam sensor or harness in theory shouldn't keep your car from starting because the PCM will just keep "guessing" where the cam is while you crank it, and eventually, maybe after a hickup or puff out the intake, your car should start and stay running once the correct cam positon is "guessed". At any quessed position, your PCM will still command the fuel injectors to fire. Although, it may not be a bad idea to inspect the cam sensor and wiring (I know its near a waterpump pulley) for rubbed through areas, and if the sensor came from anywhere but the dealer, may not be a bad idea to request a replacement.

Which leads us to the crank position sensor. I have, in my experience, never seen it where a faulty crank position keeps the fuel injectors from firing. It always kills spark to my knowledge, although, this is a dual sided permenant magnet type sensor, and I suppose it is possible that one side failed which the PCM uses for fuel injector firing pattern. Anythings possible.

At any rate, both sides of the Crank Position sensor and the Cam position sensor circuit can be checked at the ignition module connector. I forgot which wire colors. I will have to see if I can find a wiring diagram. You can verify circuit integrity by measuring resistance, but the best way is probably to measure voltage output on a scope of each circuit while the engine is being cranked. Although, most "shade tree mechanics" dont have access to said scope, so a regular voltmeter should be adequate.

PS, any codes return after the CMP sensor replacement?

I think we should go back to the basics on this one. What are you missing at your injector pulse? Power or ground? Keep in mind the PCM controls the ground side of each injector individually. All of them share the power side which is I believe a pink wire if my memory serves me correctly. Said common (pink?) wire should show battery voltage anytime the key is in the on position.


That's why I suggested to check for 12 volts between ground and each one of the terminals at the injector plugs.


Which leads us to the crank position sensor. I have, in my experience, never seen it where a faulty crank position keeps the fuel injectors from firing. It always kills spark to my knowledge, although, this is a dual sided permenant magnet type sensor, and I suppose it is possible that one side failed which the PCM uses for fuel injector firing pattern. Anythings possible.


I've copied this from the manual, I hope it helps. You're right Tim, CMP won't keep them from firing, I was wrong. CKP will control both coils and injectors via the ICM.


Camshaft Position Sensor

The Camshaft Position (CMP) sensor signal is a digital ON/OFF pulse, output once per revolution of the camshaft. The CMP sensor does not directly affect the operation of the ignition system. The CMP sensor information is used by the Powertrain Control Module (PCM) to determine the position of the valve train relative to the CKP. By monitoring the CMP and CKP signals the PCM can accurately time the operation of the fuel injectors. The CMP sensor shares 12-volt and low reference circuits with the CKP sensor. The CMP signal circuit is input to the ICM. CMP sensor is located in the engine block below the water pump, above the crankshaft pulley.

Crankshaft Sensor

The Crankshaft Position (CKP) sensor is located behind the crankshaft pulley and is connected directly to the Ignition Control (IC) module.

The 12-volt reference circuit. The low reference circuit. The CKP sensor 1 signal circuit. The CKP sensor 2 signal circuit.

The Crankshaft Position (CKP) sensor has a 4-wire harness connector that plugs into the CKP sensor and connects to the Ignition Control Module (ICM). The CKP sensor contains 2 hall-effect switches in 1 housing, and shares a magnet between the switches. The magnet and each hall-effect switch are separated by an air gap. A hall-effect switch is a solid state switching device that produces a digital ON/OFF pulse when a rotating element passes the sensor pick-up and interrupts the magnetic field of the sensor. The rotating element is called an interrupter ring or blade. There are two interrupter rings built into the crankshaft balancer. The outer ring and the outer switch provide the ICM with 18X signals or 18 identical pulses per crankshaft revolution. The inner ring and the inner switch provide the ICM with 3 pulses per revolution, each one of different duration. This is called the sync pulse. Each sync pulse represents a pair of companion cylinders. The ICM supplies a 12-volt and a low reference circuit to the CKP sensor, which is also shared by the Camshaft Position (CMP) sensor. The 18X reference pulses are passed from the CKP sensor to the ICM on the CKP sensor 1 signal circuit. The sync pulses are passed from the CKP sensor to the ICM on the CKP sensor 2 signal circuit. The ICM uses the 18X and sync pulses to determine the crankshaft position by counting how many ON-OFF 18X pulses occur during a sync pulse. With this dual interrupter ring arrangement the ICM can identify the correct pair of cylinders to fire within as little as 120 degrees of crankshaft rotation.

Oscar.

Oscar's got it covered, from here shouldn't be too difficult to narrow it down.

Just an evap code is on, I replaced the cam and crank sensor anyways today. Still not starting. The injectors all have 11.9. Volts to them. I'm wondering if the icm or a PCM driver is the culprit. And the security isnt an issue, the light stops flashing as soon as I put the key in the ignition. I think I'm at a loss at this point as where to go now without just throwing parts at it :/ I'll take the harness out and dig into it again. But it looked good when I inspected it the other day, the plastic casing is still sealed shut and there's no evidence of anything possibly rubbing

today i pulled the harness that runs from cam/crank sensors to icm and fuel. i took all the tape etc off and looked for broken wires, also tested them with meter. while i had the icm and coil block off i sanded the spot where the ground goes, re-assembled it all and car fired right up. its been firing right up all day. i think i just had a crappy ground connection.

Hopefully that was the problem. Good work!

Oscar.

I would run it and tug on that harness to see if it hiccups. I've seen those harnesses go bad.