P0200 code and misfire on passenger bank LM7

[Paul Y]

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.

P.

[Paul Y]

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.

[Paul Y]

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 drivers 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.

The only thing I have not done is check the resistance on the injectors - but cant see why 4 would fail all at once and why only on one bank?

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 there 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.

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

P.

[leegreen]

You could try swapping all the injectors from one side to the other to see if the problem follows the injectors to the other side. if it does start moving them one at a time to isolate the bad injector(s)

I'd check all your grounds and check the condition of wires and connectors, particularly on the bad side. Emphasis on grounds and connectors since it seems the entire bank is effected.

p0200 is the computer detecting an electrical issue

If the fuel pressure meets spec at idle I would not worry too much about it dropping when shut off. At least in reference to the p0200

[Paul Y]

Thanks Lee,

My thinking is that it cant be a wiring issue as the Noid light flashes, there is voltage at the injector and the PCM must be operating as the Noid light flashes.

Think I might have to go back to basics and start from the beginning.

Will be a next week issue unless I get shed time mid week.

Grrrrr.....

Very frustrating.

P.

[leegreen]

I think it could be a electrical resistance issue, there is 14 volts, it flashes the noid light but there is not enough current to fire the injector coils quickly or hold them open the full duty cycle needed. Or the ground wires back to ECU for injector signals are not showing proper voltage and resistance to ECU

read up on how p0200 is triggered.... "how does gm ecu detect p0200"

the injectors have 2 wires, one is the signal wire for the injector coil, the ECU grounds it and listens to that wire electrically for voltage and resistance. The other is 12V hot all the time ignition is on

ECU and engine need good grounds, the wires and connections for 12V and control signals need to be good. somewhere in this system is an electrical problem the ECU has detected that is messing with it's ability to control injectors. Your troubleshooting is pointing at one bank, all 4 injectors, not both banks, not just 1 injector. I'd look closely at the hot wire and and connectors for that bank as the problem seems to be common to all 4 injectors.

I can imagine a fuel rail problem starving one bank, but I don't think lack of pressure will trigger p0200.

[Paul Y]

Thanks again Lee,

Its cold and late here but just gone out to the shed again to recheck the Noid light side to side.

The illumination is noticeably brighter now the sun has gone down in the drivers side so I think your earth prognosis has merit, especially as I have had a number of earth issues already with this harness.

Will use the power of the internet to find where the PCM earths the injectors.

Thanks again.

Paul

[Paul Y]

Because this is really bugging me now went outside again and ran an earth lead from the black wire with a white trace that runs down to the back of the head.

Still the same issue.

Question.

How does the PCm ground the injectors? Is it through the case or is there a ground from the PCM to a point on the chassis?


Will have a look at the wiring diagram again as thought that's what the black/white wire was.

I could never have been an electrician.....

Paul

[LS short box]

My .02?
Yes the ECM provides the grounds to all the injectors as far as I know. That's why it's so important to have super clean ECM to engine grounds along with battery to engine grounds.
Don't know if you are on LS1tech.com but those guys over there are super sharp.

[WorldsCrappiestTruck]

The PCM grounds the injectors (to fire them) through ground wiring in the PCM plugs, not the actual case itself (though that might be grounded also). My PCM case is not bonded with an extra wire to ground. I handmade my harness and combined all GND wires into one bundle, crimped them all together under a large lug, soldered it shut and bonded it to the body of the truck (which also has several large high-quality ground straps from the frame to body, frame to bed, frame to fuel tank etc. Grounds grounds grounds.

Something to check would be making sure the trigger wire back to the PCM for the 8 injector wires, are pinned into the right location and you don’t have 2 wired to 4, 6 to 8 etc.

An issue I had (not identical but similar) was a set of Chinese coil pack harnesses I bought from Amazon that were wired incorrectly. Each side had 2 coils swapped. They’d fire, a timing light worked and showed life but they were firing at the wrong time and I could only tell with an infared gun looking at each header runner to measure temp. 2 were very lot, 2 less hot because they weren’t making full on-time combustion.

You could have the same sorta thing but with injectors?

16V seems weird - that’s a big number. What are you running for an alternator? Whatever it is should regulate voltage so it isn’t that high. Maybe that’s the crux of the whole thing? Reference voltages at sensors and the PCM are just too high making things look silly to the PCM?

[leegreen]

injectors have a common 12V source and the ECU grounds them individually to fire them.

The ECU and engine need to share a good common ground or none of the sensors read correctly, but that should not be bank specific. Bank specific issues would be the harness and connectors on that side, the 4 signal wires all the way back to the ECU in case the harness is damaged.

One bad injector could do it too, an internal short drawing down the common 12v source for that bank, so suggestion to swap all 8 injectors from one side to the other to see if problem follows injectors or stays passenger. You could resistance check each injector instead

Is the harness factory stock, aftermarket, DIY or ?
Did this engine run well in this truck before or are you still on initial startup for the swap?
The ECU itself has 2 or more ground wires, but not sure how that might play here. Other than indicating grounds are important. Generally they should ground to the same point and you want a good grounding point, not just sheet metal screw sent into a rusty fender as an afterthought

[Paul Y]

Hi Lee,

On LS1tech but didn’t have a huge response there so copied and pasted it to ‘old faithful’

The loom is a Current Performance harness, not been super impressed with it but it came with the engine.

The black/white wire - which I believe is the PCM ground - is attached to the back of the head. As above have run a jumper cable from this wire to the engine ground but didn’t make a difference.

This has really been a long term project with ‘life’ slowing it down more than anticipated. The engine did run well initially, the lack of power and misfire has become noticeable over the past few months as I start my initial drives, even if it is only around the drive way….

I have had suggestions that it is the pcm that is faulty but if that were the case the mood light would not flash showing that it is being earthed by the pcm.

Anyway, if anyone has any further suggestions please let me know but won’t respond u til tomorrow as it is my bed time!

Thanks again Lee and Mr CrapTruck.

Paul

[leegreen]

I don't know anything about that brand of harness, but I asked to get some indication of expected quality. As expressed above, some cheap harnesses should really just be considered a kit as you need to double check they are done correctly. The aftermarket connector quality could be suspect, not holding the pins tight. or a bad crimp

[cj847]

As stated by others the p0200 is likely a wiring issue.

https://www.obd-codes.com/p0200#:~:t...of%20a%20P0200

I am a little surprised that you don't have another code. If the injectors are firing but poorly, you should get a lean code. Does your code reader have live data function? You might check your fuel trims, as that would indicate what kind of fuel/air mix you are getting.

[Richard]

Probably a long shot. But a grounded ECU can cause problems in some instances. Causing ground loops and such. All necessary grounds are in the harness. Look at stock type mountings, usually in a plastic case. Though I made a metal bracket to mount my ECU I used nylon bolts and washers to secure and isolate it. Are you integrating a stock pcm as well as the ecu in the swap or just getting the terms mixed up?

[Paul Y]

Thanks for the reply Richard,

Lets just call it the Computer shall we!

I have a plastic holder for the 'computer' that is under the dash attached to metal straps. I was contemplating grounding the case of the 'computer' as had seen others state that this was a cure all....

A chap on LS1Tech was worried about the voltage I was seeing and recommended that I check the voltage at the back of the alternator with the engine running. It was 15.8V...

Took the alternator to be tested as I suspected that the regulator was faulty - hopefully will hear back today.

My thinking is that the 'high' voltage - over 16V when revved up - has burnt the inject coils. Will take them out and Ohm the passenger bank this evening to confirm that is correct.

If that is the problem I dont know why it would only be one back but beginning to run out of ideas now!

Thanks for the reply, it is appreciated.

P.

[Paul Y]

Work has stopped play to a certain extent but have had confirmation that the alternator is toast.

Good to know my diagnosis was correct.

It also got me thinking about the start/cause of these issues.

Several months back I had an Ultima battery fail, it had an internal short and managed to blow the fuel pump fuse.

Got a new battery - under warranty - and didnt think much of it as the truck is still very much a WIP rather than a daily.

It was after this that I had the no start issue, which required a new crank position sensor and a repair to an earth, as well as a hard start, long crank and lack of performance plus the misfire....

Mmmmm.... anyway, let's see if an alternator gets the voltage to the right level - the injectors ohm out and the problem goes away.

Should have stuck with a carb and points....

P.

[jjzepplin]

Interested in the outcome.

[Paul Y]

Quick update - waiting for parts.

One of the many downsides of running an American car/truck in the UK....

P.

[leegreen]

fuel issues wont set p0200

[Paul Y]

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.

Appreciate your help.

P.

[leegreen]

you still have the situation where unplugging injectors on one side make a more noticeable RPM drop that the other side?

check the resistance of the 12 V feed to the injectors on that bank

check resistance of each injector

try swapping all injectors from side to the other to see if the problem moves

[Paul Y]

Thanks for the reply Lee,

Not unplugged the injectors yet but will get a few hours in the shed tomorrow and try that first.

Will also check the Ohms on the injectors - have a spare set so if required I can use them.

What should the resistance be on the 12v feed to the injectors? Do you know off hand? if not will consult the great Google.

Thanks again, will report back tomorrow.

P.

[leegreen]

I'd google it. Lacking an informed opinion from the great AI I'd make a close visual inspection of the harness & connectors, then compare resistance at each injector connector on both sides of the engine, see if there are any anomalies to harness.

if nothing found, then resistance check each injector to see if they are all the same

if nothing found then swap all injectors from side to side to see if the problem moves

[WorldsCrappiestTruck]

Originally Posted by leegreen

if nothing found then swap all injectors from side to side to see if the problem moves

Honestly this is the first thing I’d do. Just pull the fuel rail, swap left to right, and see what happens. If the problem stays with the bank, look at wiring. If the problem moves with the injectors, look at fuel.