HELP!! 8.1 Engine Not Starting (Sometimes)

[Team208Motorsports]

Is there any possible way you could post or email me a copy of the tune?

 

[GMCbigblock]

Is there any possible way you could post or email me a copy of the tune?

I just contacted the tunning-shop & their Owner informed me that they cannot release the tune!

And, I know for sure that the Tunning-Specialist has been professionally-trained at various reputable tunning-centers in the US.

Sorry & thank you for trying to help.

 

[Team208Motorsports]

Well, that sucks. Not surprising though.

Was there any problems before the tuning?

 

[Jumppr]

VATs? I gave the same engine (2003) and it would start then shut off immediately. This doesn't sound like what's going on with yours, but it's worth a look. My friends own a shop and they were going to give me a spare computer to swap in and see if it made a difference. Might try that if you have the ability.

 

[Team208Motorsports]

Vats causes a fire and die. No start is a totally different thing. No start on a speed density tune is common if its not setup properly.

 

[Jumppr]

Yeah.....That's why I said I didn't think it was VATs. My truck is stock with no tune upgrades so I don't know how that effects the rest of the function. Also, mine is an 3yrs older and maybe a little different.

 

[GMCbigblock]

Yeah.....That's why I said I didn't think it was VATs. My truck is stock with no tune upgrades so I don't know how that effects the rest of the function. Also, mine is an 3yrs older and maybe a little different.

Just to note, due to time-zone difference, we are about 12 hours apart (our local-timing is ahead).

Answering all your good-queries:

- Yes, the car was different before the tunning, as it did not have this issue before.

- Am thinking to switch back to stock tuning setup, using another ECM.

- Recently I replaced the Knock-Sensors of Banks 1&2.

 

[Team208Motorsports]

- Yes, the car was different before the tunning, as it did not have this issue before

It sounds like they, the tuning shop, are not that good. I would tell them your issues and see what they can / can't do.

If you like I can ship over an ECM ready to go. I would just need your vin.

Is your mass air flow still in the system or was it phisically removed?

 

[GMCbigblock]

I highly appreciate your offering of such a support. Will keep this option on the boiling-plate.

To be fair & for info, the Tunning-shop is currently using exactly the same setup & way of Tunning for his 2005 Crew 8.1 Chevy (Auto), with no issues!

Answering your query, Yes, the MAF is still physically in place, but its value is set at Zero (Off). I believe it was functional, before deactivation.

Now, while thinking about shipping the new ECM (after supplying the VIN), would it be a good idea to use "Howell" reduced-harness/wiring along with the new ECM?

For info, am currently using their product on my "8.1 Blazer, 1981 Project" - with no signed fault or issue for the past 4-5 years. Hat off for all quality products.

 

[Team208Motorsports]

I'm sorry but even if it is in place it can not be deactivated by just setting a value to zero. It still has to fault out first. Once faulted and still in place the ECM still uses the registered MAF reading for dynamic air calculation. MAF in place and hooked up is when the speed density no start occurs the most. I would say they are not faulting the MAF correctly.

Is this engine in a stock truck? If so, there is no reason for an aftermarket harness when your problem seems to be tune related.

If you want to see whats really up put a stock tune back in it. If it goes away, you know the tuning shop lacks the experience to handle a simple speed density tune. I tune remotely around the globe, most of which are speed density tunes for race application. A stock engine with a speed density tune is already in place about 80% of the way but has to be setup properly.

This generation of ECM has a airflow processing path of this, simplified....... When the MAF is in place there is an AIR Flow calculation RPM. With the MAF in place anything under and the ECM dynamically calculates air flow based on ECM calculated and MAF air flow. Anything over that number and it solely uses the MAF reading. GM does this delay to let the air flow stabilize in the MAF first. With the MAF gone and the ECM setup to properly fault the maf the ECM totally dynamically calculates the air flow without the MAF reading. This is true speed density. If the MAF is still in place and hooked up it will use these value in the dynamic calculation even if it is faulted. Depending on how it is setup in the tune for fault it will try and use the incoming MAF reading before faulting.... This will give a very lean mixture and either cause a fire and die or no start.

 

[Team208Motorsports]

I'll go into a little better detail.

Here you can see the set point to go from Dynamically calculated air to only using the MAF. Some guys set this number very low and try to only use the MAF, while this works on the drag strip staging and launching.. It has zero real world app for a precise running engine.

Lets move on to the actual fuel table. I will post a later tune and then an early tune. You can clearly see where GM had these tunes set for the MAF to take over. A true speed density tune would have this table fully defined.

2006 8.1

2001 8.1

As the years went on GM further tuned the speed density side.... That tell you anything?

Now on to faulting the MAF.


This table is used for when and where to throw a MAF fault. If this is not set properly it will not let the MAF fault processing even begin until the engine is running. Thats not good for speed density.

This sets the type of fault the ECM should set and how many times it takes that fault to set. If this is not set properly it will cause the ECM to NOT fault the MAF properly. This is where you get the lean start and run that causes fire and die or no start.

These are all stock values for using the MAF as in stock app. I'm not hear to teach how to do it but I will gladly show where and describe what the tables and setting are for.


So now..... Lets talk about the MAF for a few seconds. The maf has a calibration table of its own. It is calibrated for the stock intake tube, filter and maf used.... If you were to put a cold air intake on this rig it would HIGHLY alter the flow to the MAF. If the tube is the same size and the MAF is in the same location once air stabilizes its usually not that big of a deal but it will have totally messed up the dynamically calculated air. This is why most systems say the ECM has to learn.. Its not learning anything other than long term fuel trims. Thats not the correct way as the dynamic calculation is now totally off. Sure that intake sounds cool but now you have a ecm that is relying on long term trims to be correct. All base fuel calculation is now incorrect. The same can be said for speed density as you have now changed how the air can fill the cyl.

 

[GMCbigblock]

I'll go into a little better detail.

Here you can see the set point to go from Dynamically calculated air to only using the MAF. Some guys set this number very low and try to only use the MAF, while this works on the drag strip staging and launching.. It has zero real world app for a precise running engine.
........
So now..... Lets talk about the MAF for a few seconds. The maf has a calibration table of its own. It is calibrated for the stock intake tube, filter and maf used.... If you were to put a cold air intake on this rig it would HIGHLY alter the to the MAF. If the tube is the same size and the MAF is in the same location once air stabilizes its usually not that big of a deal but it will have totally messed up the dynamically calculated air. This is why most systems say the ECM has to learn.. Its not learning anything other than long term fuel trims. Thats not the correct way as the dynamic calculation is now totally off. Sure that intake sounds cool but now you have a ecm that is relying on long term trims to be correct. All base fuel calculation is now incorrect. The same can be said for speed density as you have now changed how the ecm can fill the cyl.

MAN! Although I kept pace with some of the useful-contents, in overall your 'chain-of-emails' kept my eyes wide-open at full-throttle ....Truly appreciate it, as it did help me in better understanding of the terms used behind the tuning-screens.

For an idea, the Truck is OEM fitted with 8.1 Engine being GM's production (our Gulf Specs; Emission wise), and it carries the following VIN:

........

Also, it has a "Cold-Air Intake System by "VOLANT", which truly changed the way the Engine used to respond. I liked it. Further, the Truck does not have the last "O2 Sensors" installed, only the 1st set of two (as per the tuning).

Now talking resolution, it appears more visible to replace the Truck's existing ECM & go the way you suggested. However, one thing I like to share is that, I once bought a "pre hot-tuned ECM" but it did not function properly in my country. I believe this may have occurred due to 'local geo parameters'! The 8.1 Engine (2001) used to crank but runs rich "smokes" & backfires "detonates" at the acceleration & hesitates all the way.

So, what say you have? Way forward?

 

[Team208Motorsports]

I'd be happy to send an ecm and give it a shot. I needed the vin so I can flash the ecm first from GM, your geo would be attached to the vin. So it will be to proper base flash. To see about resolving the issue, I would like to first know if the MAF has been altered at all? Have any wires been removed from the MAF plug? Is it physically still in the proper location and functioning minus the speed density tune? What fuel do you have, octane wise? What is the tire size and gear ratio of the truck?

All I'd ask for now is to cover the shipping and the cost of the ECM. I buy the gen 3 ecms for about $30 used and I would have to get a shipping quote. Once we have established everything is properly working we can discuss remote tuning, if it needs it. May I ask why was a speed density tune put on the rig?

Admins, I'm sorry if this oversteps my bounds on the forum and if this needs to be moved to PM please let me know.

 

[RubberFloorMat]

ok, so when it does the no start, it cranks, but will not fire? have you tried resetting the ECU by pulling battery cable etc?

 

[Team208Motorsports]

I already burned an ECM with you VIN and flashed it from GM. Your Emissions code is awesome! No rear O2 processing, no evap processing, no fuel tank pressure processing, no cat processing. By processing, I mean there is no fault diagnostics enabled.

Feel free to edit your post and take your vin down.

 

[GMCbigblock]

ok, so when it does the no start, it cranks, but will not fire? have you tried resetting the ECU by pulling battery cable etc?

Yes, I did & it still continued giving "no start".

 

[GMCbigblock]

I already burned an ECM with you VIN and flashed it from GM. Your Emissions code is awesome! No rear O2 processing, no evap processing, no fuel tank pressure processing, no cat processing. By processing, I mean there is no fault diagnostics enabled.

Feel free to edit your post and take your vin down.

Great & appreciate noting such a prompt response.

AccordinglY, I edited the VIN info.

As for some queries on the Truck, it has 4:10 Rear, Stock MAF is installed & the wiring is in its original pattern as per the OEM fitting. The current tires are almost 35 inch. (315-70/17).

And I don't have a clue about the tuning as why speed tube used. But it could have been used for waiving the MAF & make the truck less tech dependant & hence increase its reliability against code-faults in our hars environment (extreme heat & dust)! Note, gas is cheaper, relatively. Locally, we have 95 & 91 Oct. Fuel (Lead-free).

Will wait for the further details to move on with getting/shipping the ECM, tuned to the VIN specs.

Last note, am now out of country on travel via road, and will be frequently doing remote-desert offraod till Sat/Sun! Hence, we may be occasionally out of signal-reach & network-coverage. I'll try remaining in connection as the situation permits.

 

[Team208Motorsports]

If the MAF is intact and good I would like to go ahead and send an ECM with some decent tuning. Once installed and verified things are better we can go from there. Send me a message with your email and shipping info. I can get this out and to you so we can test.

 

[GMCbigblock]

If the MAF is intact and good I would like to go ahead and send an ECM with some decent tuning. Once installed and verified things are better we can go from there. Send me a message with your email and shipping info. I can get this out and to you so we can test.

1st - Sorry for being disconnected for a while (was out of Data-connection & signal-coverage). And yesterday, I reached my home-town.

2nd - Yes; the MAF is intact. Accordingly, I'll proceed as suggested very soon.

 

[GMCbigblock]

And to all contributors,

I like to repeat my appreciation to the value-added discussions....Looking forward to sustain with the same in the future.

And, I'll keep this "Thread" updated with the outcomes, as & when reasonable-progress is achieved towards resolution.