Gents,

On struggle street and could do with some advice

LM7 swap into a 66 C10.

Stock PCM stock engine.

After my non start problems, solved with a crank position sensor. I have now developed a P0200 fault.

I have a Noid light which shows that there is signal to all of the passenger side injectors.

When I connect the harness back to the injector I can hear it clicking so is firing.

It sounds like the bank is firing but not as strongly as the driver’s side as when I disconnect an injector on the driver’s side there is a big drop in idle but on the passenger side it is very ‘light’.

Definitely has spark.

Fuel pressure is 58lb.

I would suspect injectors but not all on one bank.

Next check will be continuity from the pcm to the passenger side injectors.

Anything else I should’ve checking?

Appreciate your assistance.

Paul.

 

Also throwing a can position sensor fault as well now.

Could that cause one bank not to fire?

Possibly not as I have 14v to the plug when I test it- the Noid light pulses so that shows there is a signal from the PCM but still shows a P0200 fault

Apologise chaps using this as a sounding board to work through my thoughts.

if anyone wants to chip in would appreciate it as not sure what else to check.

 

Whilst scratching my head and checking voltage noticed that my fuel pressure gauges had dropped to 20psi with the engine switched off and continued to drop to 0 over the next few minutes.

Turn key to prime the pump and pressure goes to 58lb but as soon as I turn the key off pressure drops almost immediately to 40lsi and the drops down to zero pretty quickly.

Mmmmm… as you can probably tell don’t really know what I am doing but trying to approach this in a logical way.

what did I learn today then?

• There is 14v that the injector when tested with a volt meter
• When I attach a Noid light to the injector harness it pulses indicating that the PCM is firing the injector
• The injectors are new, admittedly finest Chinesium but they are all good on the driers bank and can’t believe that they would all fail on the passenger side
• Fuel pressure drops rapidly after switching the engine or pump off.
• There is now a cam sensor code.

Could the drop in fuel pressure point towards a stuck injector or maybe a lack of fuel pressure to the passenger bank? I am running stock truck manifold and fuel cross over.

Bit stuck so if there is any advice would appreciate it.

Paul.

 

As you can tell this is driving me a bit nuts....

Just had another thought. Have gone and checked the voltage at the back of the alternator and it is 16V. Have checked the voltage at the injector and it is 16v with the engine running, 14V with the engine off. If the voltage is too high and causing the injector to burn out? Voltage is same on both banks.

One thing I have not checked is the o2 sensor on the passenger side. Could that cause the PCM to throw a P0200 code?

 

At 16 volts, you are on the ragged edge of frying your powertrain control module. Fix that before moving to anything else. A bad ground is often indicated when an entire bank is having trouble.

Which PCM do you have? A red / blue connector or a blue / green connector?

Rick

 

Blue/Green.

I think I have narrowed it down to a bad earth as you say, or at least an earth that is not as good as it should be. The part that has made me question myself is the Noid light flashes when connected to each of the injector harness in turn so the PCM is grounding the injector but maybe not well enough to open the injector enough?

From reading more it would appear that I need to check the black/white earth that bolts to the back of the head.

Looking at wiring diagrams it looks as if the PCM earth is on the green connector, position 1 - is that correct as the diagram I have looked at also says it is black/red??

The loom is a current performance harness for clarity.

Not quite sure why the battery voltage is so high, will have to check it again.

Appreciate your reply Rick - good job I dont have hair right at this moment in time......

Paul

 

Hello Paul,

This might help you with the pinouts on the blue / green PCM. You very likely have a failed voltage regulator in your alternator. I'm usually at around 14.4 VDC at the battery if it is already fully charged with the engine running and a vanishingly small amount of ripple leakage past the rectifier diodes - never more than .05 volts of alternating current.

https://lt1swap.com/2004vortec_pcm.htm

Rick

 

Thanks Rick,

Will check there and report back.

Paul

 

Rick,

I think you might have cracked it.

Voltage when engine is running is 15.8V at idle....

I have Ohm'd the injector on the passenger side I can get too and it is showing 0. This was all done this morning before I left for work so will have another go this evening but I beginning to think the injectors are fried. But only on one side?

I wonder if this could also be the reason why the fuel pressure drops when the engine is turned off as the injectors could have failed open?

Not the most scientific reply but will dig in a bit deeper this evening as well as taking the alternator off to get it repaired.

Will report back later.

Paul

 

I have no idea of what exact injector type you are running as to it leaking or not. It's just as likely a faulty check valve in your fuel pump assembly. Nothing fatal there but it might take an extra ignition key activation to get fuel all the way back to the rails. Mostly, an annoyance.

Rick

 

if you had a leaking injector that bad it would likley hydro lock the engine and bend a rod.
Deffinatly sounds like a bad ground as previouly mentioned more than once.
And yes, a weak ground could easily flash a noid light but now flow enough current to open an injector.

 

To add to this discussion here guys, the injectors have a constant voltage to them and the ECM sends the ground to complete the circuit via flashing or pulses. Coils are grounded via the neg battery side…chassis ground…. so they are much more “ground dependant” than the injectors.

 

Happy New Year to you all and I trust your Christmas was relaxing.

Back on this today as the parts to fix the alternator arrived and have been fitted. Good news - now have voltage around 14.6v so that appears to be fixed.

Now back to the problem of the p0200 code.

I disconneted the earths from the rear of the passenger side head, cleaned up the connectors and sanded the head - reinserted bolt, cleared codes started engine and... still showing a p0200 code.

Take the earths back off, strip loom back and test continuity of earths back to where earths join together - not a great desciption but if you have stripped a loom you will know what I mean - all test fine showing no break between connector and the afore mentioned junction.

Run connectors to the shared earth from the battery.

Clear codes, start engine and... still showing p0200 code.

At this stage it is -1c in my shed so have retreated to my sofa to thaw out by the fire, drink a glass of wine and finish off what remains of the Christmas cheese as I am at a complete loss now.

What have I missed?

What else should I check, test, try?

Really would appreciate any suggestions.

Apprecaite your help.

Paul

 

Paul,
I fought an intermittent P0200 on my Chevy II for years, drove me nuts trying to fix it. I had the same theory that it was the grounds on the back of the head, but they always checked good. I finally got fed up and ran a dedicated ground from the frame to the back of the head on top of the injector grounds. Oddly enough, it seemed to fix the issue, I have not seen another P0200 in years. It may not solve your issue, but hey, It is worth a try.

Edit: rereading your last post it looks like you already went straight to the battery negative.

 

Did you do a cps relearn when you replaced the sensor?

I had a P0200 and went through all the usual checks on my LM7. The relearn I did with my bi-directional scan tool did the trick .

A thought.

 

Gentlemen,

Many thanks for the response, I really appreciate it.

i am going to start from scratch and go through my check list, below, as this must be something simple that I am missing.

1. Check grounds.- grounds currently run to battery negative but will check continuity of earths back as far as I can, hopefully to ecm.

2. Check power to injectors - believe this should be at least 12v with ignition on.

3. Check resistance of injectors - believe this should be between 10-14ohm

4. Use noid light to check signal from ecm.

5. If all else fails push the truck to the middle of the garden and set fire to it……

Rick, I only have a cheap code reader that won’t enable me to do a relearn - being in the,UK not a lot of people have the software for GM vehicles, I know sacrilege…. Does anyone know of a cheap (free) program I can use? If not will have to wait for my post Christmas fun cash to replenish and enable me to get a reader and software.

Mind you, I am a 1/3rd of the way to getting HP tuner pro with the cost of the reader and software so might just have to save up a little more!

The annoying thing is that I have checked all this stuff more than once and each time everything check out.

Anyway, I have ordered a new cam sensor as this is also showing a fault and I have read that this could be a possible cause of one bank not firing the injectors. Rock Auto to the rescue with a Delphi one arriving on Monday.

From my list above is there anything else I should include in my check list?

Once again thank you - virtual beers to you all.

Paul.

 

If you were nearby, I would give you a spare PCM to try. A faulty PCM is usually the last possible thing it could be as these are usually very reliable. Nevertheless, having a spare sitting around on the shelf is a great diagnostic tool and they are cheap at maybe $45.00 USD in the junk yards around here. Then tune it for free using the PCM Hammer software application.

Rick

 

Latest update for those following along.

1. Earth not checked but wait before you jump on me!
2. Power to all pink injector wires 13.3v
3. Resistance to all injectors between 9-11ohm - majority were at 10ohm
4. Noid light is bright and pulses across all 8 injecctor harnesses.
5. Brakes stuck on so cant push it to middle of garden - yet.

As for 1.... Well at this stage the earth leads are using the same connection point as the engine earth PLUS if there was an earth problem then the Noid light wouldnt be so bright and flash with the same intensity across all injectors - Or have I got that wrong?

Battery is currently charging but will go back and check the earth to the ecm later in the day.

The engine is hard to start and backfires into the exhaust - as I mentioned earlier I have a cam sensor fault as well so will replace that with the Delphi one when it arrives and see if that fixes the problem.

Forgot to mention that I also swapped the injectors side to side and the fault has not moved..

This truck is really fighting me at every opportunity, but, on a positive I have learnt more than I ever wanted too about trouble shooting - even if I am not good enough to actually pinpoint the fault!

Anyway, will keep you updated.

Paul

 

Been a few weeks but a combination of waiting for parts, the cold (it has been down to -11 Communist here) and general Meh has dampened my enthusiasim some what.

Anyway, an update and a further request for help.

Cam sensor was replaced with a Delphi unit. No change, still a p0342 code.

Checked voltage to plug. No Voltage. Ah Ha!

Whilst there i also checked the earth by connecting my multi meter to a live and checking voltage. Came back at battery so thats all good.

Stripped back loom and found a previous repair on the power wire, by previous repair I mean a bit of duct tape loosely wrapped around the live.

Checked voltage on the 'clean' side of the repair and 12v. Possible smoking gun found!

Made repair, cleared codes and..... well the p0342 code had gone but still the p0200.

Bother.

Borrowed a friends proper code reader rather than my £5 Ali Express version and splashed out £60 on buying the GM diagnostic module.

Read the codes and can now see a p0605 code which my previous reader cant see.

Plugged in my China reader just to see if the code was there. Nope. So maybe not a waste of £60.

Battery voltage is a bit low so charging the battery and see if that fixes the issue - I know its not but I can only hope!

One of the guys on Sloppy can sort me out with a PCM as I think that is the only thing it can - will juat have to wait for it to arrive.

Question for you more knowledgable than I

On the cam position sensor live I am seeing about 12v. Is this right?

Let me know.

Paul

 

Latest update.

Dsiconnected battery and shorted out the + and -

Left for a week, some of us have to work....

Thought I had found the problem when I found a random earth wire sticking out of the harness. Was just the end of a wire that was earthed in a bunch with 3 others.

Bother.

Ended up cutting and resplcing the earths together anyway.

Went through PCM earths, ohmed out at the connectors and the earth connections - all good.

Reconnected battery, started truck. Still missing on passenger side.

Read codes.

Still showing the P0200 code and the p0605.

Went back and stuck the noid light on all the injectors.

All flash bright.

New PCM arriving Tuesday - really cant think of what else it could be.

Paul