PGDimpala

Hi,

I am hoping someone has some insight or a good suggestion for me to check. Without going into to much detail I will just ask what might be the issue if I am only getting coil logic fire signal on coils 5,3,8 and 2?

Interesting thing is that it is every other coil in the firing order ie no 1, fire 8, no 7, fire 2, no 6, fire 5, no 4, fire 3. This interests me as I feel like this is not coincidental.

I suspected wiring but from pcm connectors to all coil connectors signal to pcms pins are good. All coils also getting 12v and have grounds. Also its not just one side of engine coil harness, affects 2 coils on both sides.

Could pcm coil signal driver be bad? Like a bad pcm?

Any suggestions for diagnosing. I have a few crank, cam, and coil scopes I could post. Far as I can tell I have a good ckp and cam signal. Both if which are getting to pcm.

Thanks, Paul

PGDimpala

thought I would post some more details on this. This one can be a real challenge for someone!!! I appologize for the long read, but i have done a ton of diagnostics and to limit questions to get everyone up to speed quickly i will post everything i know.

Hopefully someone very savvy in the ways of the PCM and its signals can tell me what is wrong with my setup or if my PCM is just flat-out not good.

Injector wiring from PCM to injectors are good. Continuity from proper PCM connector pins to individual injector connectors.

All injectors have batt 12v+ when in run.

All pcm batt+ (Blue 20/57) and ignition batt+ (Blue 19) are good

All PCM ground pins are good. Pins 1 & 40 on Red and Blue.

All coil connectors have 12v+ ignition power in run

All coil connectors have proper signal wires. Continuity from PCM connectors to individual coil connectors is good and proper pins.

Coil connector to engine block grounds are good.

Coil connectors PCM low ref to PCM pins continuity is good.

Plugs are brushed and blown clean. Engine is pumped clean from any flooding situation. All subsequent tests have been done with injector fuses and fuel pump fuse pulled. Injectors all fire which was causing flooding on cylinders that don’t have firing coils.


All spark plugs product spark if coil is proper signalled and fired.

Battery drops voltage quickly from a charged state of 13-14 volts down to 12.5 volts. Thought this might mean bad battery causing all my problems but in subsequent tests with a known good battery result in same coil firing problem. So not bad battery.

Have 11.5 volts at battery when cranking.

Coils 1, 4, 6, and 7 are not signalling to fire. PCM is signalling coils 2, 3, 5 and 8 to fire. Coils that are being signalled are producing spark at spark plug. No signal directly at coil connector or at PCM connector. So PCM is not sending signal at all.

Moved coils around. Does not solve issue. Coils are good. PCM not signalling is problem.

Removed CMP sensor. No affect. Still signals 2, 3, 5, and 8 only.

CKP and CMP signals appear to be fine and getting to the PCM. More questions on cam signal however. Accuracy and voltage requirements. I feel like the CKP/CMP 24x/1x signals are good as otherwise fuel injectors and 2, 3, 5, 8 coils wouldnt signal like they are.

CMP signal ‘rise’ is approx 8 degree early. See scopes below. Could this be the Problem??

CMP signal ‘drop’ is approx 0.8 degree early. See scopes below. Could this be the Problem too??

CMP voltage is low (9-9.2v) when cranking with all system hooked up. Ie PCM, Coils etc. Why low???

CMP voltage is fine (11-11.2v) when PCM removed and checking signal at connector pins. So signal is good if nothing else running. So I do need to figure out why signal is low when cranking and not low when just testing at pins. Checked grounds, low refs, etc. Anything else i should check? Maybe PCM not supplying good voltage? I am betting PCM is not supply good voltage. I will check this with scope soon. In either case tho if I have good voltage or dont have good voltage at CMP sensor still doesnt fire all coils.

Cleaned engine harness ground. No diff in CMP signal low voltage during crank when everything else hooked up.

Hooked up 12v dedicated source to CMP sensor. Then with everything else hooked up and cranking had 11-11.2v signal. Made no difference to coil firing.
Doubting CMP sensor voltage is issue then. Perhaps alignment is still tho.
No difference with MAF sensor unhooked to force into speed density.

I have debated that I perhaps need to do a crank relearn as i have never fired this engine with the new LS1 PCM, etc. So one would think i would need to do that. However i dont have access to HP tuners or other software and cant get engine running to do crank learn anyways.

Now onto some scopes......I have a ton of scopes so if someone wants to see a question answered via scope I may have it and can post. Just posted these for reference as they show quite a bit.

24x Signal. 1x Cam signal. Coil 12v igntion showing coil fire dips. Purple line is #1 coil signal showing no signal.





24x crank signal blue (0-5v) <br/>1x CMP signal..Yellow<br/>#1 coil purple (no signal)<br/>Green line is coil 12v+ in run. Dips show coils firing 2, 3, 5 and 8.

Next scope is showing 24x and 1x signals. CMP 1x signal is proper voltage because in this scope i gave it dedicated 12v at CMP sensor.




Purple is CMP signal. 10.8v or so with dedicated battery voltage<br/>Green is 24x CKP Signal.

Next scope shows CMP falling voltage is a little bit off of 24x signal 4th small step falling edge.




Falling edge of CMP signal approx 0.8 degrees of 24x signal. Very small amount. Not sure if big issue.

Next scope is showing rising edge of CMP signal is off of 24x signal 4th small step falling edge. This one is off quite a bit (~8deg), which concerns me. However remember i am still getting 4 coils firing. So perhaps this small amount leads to only some coils firing???? Not sure...anyone??



Last photo just proves dips in 12v line are coils firing. Here i scoped the #3 coil which does fire. As you can see the purple line shows the pcm coil fire signal matching with its 12v line dip. I also tested spark plug and it is sparking as well. So i am definitely gettign spark....just only on 2, 3, 5, & 8!!! so frustrating.

Paul Bell

iTrader: (9)

I was gonna ask the vehicle, year and engine but as it's a 24x, it's LS1/gen III style.

As you've shown all to be good but the PCM is not sending the trigger to the coils, I would suspect the PCM itself. Swap it out and see if the problem goes away or stays.

PGDimpala

Thanks for your input and review. I have a couple more things to check, or probably just re confirm but I too am feeling the pcm is not good. Its a brand new delco reman, but hey computer **** breaks all the time.

I am going to have to find another one and test.

FyI the car is a 96 lt1 impala ss with my own design 24x conversion. Uses ls1 pcm. Once I get it running I will share more details. Potentially bad pcm was one issue I wasnt expecting.

Paul Bell

iTrader: (9)

Interesting.

Has this combo with this PCM ever run?

LT4T56Monte

If I am reading your OScope images correctly, check your CMP & CKP voltages. It looks to me like your crank signal peak is 5 volts and the cam signal peak is 12 volts. Check for 12 volts at both the crank and cam sensors. Both need 12 volts. Both sensors should have a 12 volt peak signal. Attached are the signals from my 05 Vette. It is an E40 but a 24 tooth engine w/ same sensors. If the CKP signal voltage to your 411 ECM is too low. the ECM will not see the signal. It will try to start by guessing off of the CMP signal. Are you getting any codes?

Old Geezer

iTrader: (3)

Updates??????????

PGDimpala

Sorry for no response last fall. Finally got the problem solved that last week in october. Was an issue with reluctor. Solved it 100% and then it started right up. Then immediately put the car in storage for the winter.

fast forward to now....

Just got the impala out of storage for the 2015 season. Still running good. Need to adjust tune for tach signal pulse, its currently reading 2x high. Also dealing with starting issue. Have to give it slight bit of throttle when cranking then starts fine and runs fine. If dont give it just tiny bit of throttle during crank/starting it will stumble and run rough til i give it throttle. Then runs fine, idles fine and runs strong.

Going to do a CASE relearn via hp tuners and see if that solves. If not move onto iac, tps diagnosis/tuning.

Or any other suggestions anyone might know i should check?

thanks for everyones help last fall. Overall l have successfully completed converting my impala to 24x gen 3 engine management with my own design components. No timing cover removal, no LT harness rewiring, high performance 24x and 1x signals, works on any year lt1/4, coil on plug, and takes probably 3hrs or less to install (if u know how to r&r opti). I will give much more detail soon here and over on impalassforum.com

Paul

RonSSNova

iTrader: (3)

Very nice work Paul.
I was gathering parts to convert my big block, but the turbo LS bug bit me and the rat is long gone.

mrvedit

Please tell us more about the reluctor problem. Was it loose or bent?
You have me curious now what a proper CKP signal looks like; may have to scope it myself , especially to see the timing between the CMP and CKP signals.

PGDimpala

The issue was backwards crank reluctor. I checked this more than once but if u look at pattern it is almost identical, especially at sync points with cmp signal. so every time i questioned i thought nope looks right. Then one night i looked at every rise and fall and then spotted it. tough to see when holding disc in hand but saw it when i looked at middle of pattern on scope. Now we all know that 4 cyl will fire with backwards reluctor. Takes correct way for all 8. Once i swapped it around and kicked myself for not seeing sooner it fired and came to life as best i could hoped for.

I still plan (have solution) on fixing my cmp to ckp 8 deg misalignment. This is something i discovered once analyzing characteritic of cmp sensor. The amount of detailed information i have learned about various components during development could fill pages.

Paul

Troberts56

Need help im facing the # 1 7 4 6 coil not firing the reluctor wheel hasn't been removed anyone have any suggestions I have power at the coils .08 ohm on my ground wire on every coil just no signal to fire from the pcm

G Atsma

Start your own thread instead of tagging onto a 5-year old one.

AGREED - As moderator I am closing this thread.