1994 454 TBI runs rough, misfires, backfires, dark exhaust

Froggy1936 · February 25, 2016, 02:28 PM

http://www.truckforum.org/forums/general-truck-forum/36427-everthing-need-to-know-about-a-4l60e-4l80e-2.html Here is a link to troubleshooting the 4l80e a lot of good info The TPS is a cause of no shift make sure it is operating and you reinstalled the connector fully Good Luck

Frank

kennyrodgers · February 25, 2016, 05:46 PM

Thanks Frank, I'll give a that a good read through and we'll check for codes on Monday.

Whilst I'm here....
There's conflicting advice on what the vacuum type item is in the top of the picture. It's actually on the left side of the TBI looking forward. Is it for the cruise control of is it a throttle kicker.
The reason I ask is as per my previous I noticed the throttle stop was resting on the bolt head and the butterflies were slightly open as a result. I wound the bolt in a few turns but it didn't really affect the idle. I mentioned this to my friend and he thought that the IAC and ECU would control the idle if it needed a boost because the AC was switched on.
If I could get a definitive answer that would be great. Also, me winding the bolt head in wouldn't have any effect on the shifting problem would it ?
just checking.

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SLEETH · February 25, 2016, 06:24 PM

it is a vacuum dashpot=never seen one on a tbi unit
the iac does control the idle through the ecm/why not just remove this temporarily and see if this rectifies your hi idle issue

kennyrodgers · February 25, 2016, 06:44 PM

Hi Sleeth,
Didn't manage to get a pic of the OBD connector after all. Got held up at home before work so didn't get chance.
I did back the nut off but and the idle has dropped. Once I've figured out what it is I can decide if it's need or not. If not then I'll make it redundant.
The idle when cold is still not quite right though as it's not steady. I've still got black smoke and misfires (no backfires any more)when cold despite everything we've done up to now. Once she's warmed up though she seems to run a lot better with a crisp throttle response.

SLEETH · February 25, 2016, 06:48 PM

it might need a new temp sensor for the ecm=if u are getting black/rich condition when cold=this in part controls the dwell time for the injectors

Froggy1936 · February 25, 2016, 07:01 PM

Did you replace the o2 sensor yet ? This can cause rich mixture Frank

SLEETH · February 25, 2016, 07:13 PM

are there any wires running to this dashpot thing?

SLEETH · February 25, 2016, 07:15 PM

one silly question? have you the correct wires going to the right injector? (ive seen these reversed causing running isues)
had t ask

SLEETH · February 25, 2016, 07:17 PM

question =the cruise cable not hanging up the throttle return?

bluebird · February 25, 2016, 07:41 PM

Remember this is a propane conversion, it's going to have things on it that normal gas units don't have.

kennyrodgers · February 25, 2016, 08:04 PM

Lots of questions.......all welcomed btw.
Re the injectors, we have no clue if they're wired correctly tbh as the wires were melted and hard wired to the tops of the injectors without using the correct connectors. We've since fitted correct connectors but wired a + and - to each. They could be mixed up so I'll try swapping them around to see if there's any change. The other thing is we could have the + from one and the - from the other.....my head hurts.
We changed the CTS sensor at the front of the block, I'm pretty sure that's the one that goes to the ECU for the engine temp.
Re the o2 sensor....i couldn't get the dang thing out Frank so not yet. My buddy is coming over on Monday with the correct removal tool, ie , deep socket with a hole for the wire. I'm hoping that once we get that done we'll start to see a change as I'm pretty sure that the one that's in there is the original from 94.
The dashpot thing is factory so not connected to the propane set up. The only thing out of the ordinary on top of the engine is that the injector sits atop the air filter housing.

Rickf1985 · February 25, 2016, 08:38 PM

It has been quite a while since I worked on a TBI but I am pretty sure the injectors fire together, there is no right and left since they both fire into the plenum. The O2 sensor is the most likely cause for the rich condition and it is senseless to try to adjust anything until you have the mixture right. There is no way it will run smooth if it is running rich. Your best bet on that sensor if it does not come out without excess force with the socket is heat from a torch on the fitting.

M & J · February 25, 2016, 09:09 PM

Me and Dave love OBD1and all but the coach and the VWs on our vehicles run it.
When the engine is cold, it runs in open loop and the O2 Isn't being used by the ecm. Not until the engine is warm (and the O2 is hot) does it go into closed loop and the ecm uses the O2 to manage the mixture.
And Rick, you are correct: both injectors fire simultaneously. You can hook a timing light up using any plug wire trigger and look at the spray pattern from the injectors. You want to see a fine cone pattern with no breaks or drips. There is also a calibration process for setting the IAC but it escapes for the moment. Should be able to Google it, not difficult.

Froggy1936 · February 25, 2016, 11:36 PM

You do not need the special sensor socket to remove the o2 sensor cut the wire and use a regular deep socket. You only need the special socket to reinstall it . Or use a box wrentch Frank

SLEETH · February 26, 2016, 07:29 AM

just unplug it & slip over a 6point wrench and out she comes

DaveVA78Chieftain · February 26, 2016, 08:08 PM

As far as TBI ref info for this configuration, I doubt GM changed much during the TBI years (early to mid 90's). So, if you have not already done so,
Select the Members Area->Manuals, Diagrams & Tech Info items at the top of the page.
Enter the username/password info from the site e-mail Mark provided you
Select Chevy/GM P-30 Chassis from the TOC
Scroll to the bottom of main and sub pages to the line for 1991
Download the following manuals:
X-9136 GMC Truck TBI Fuel and Emissions
X-9140 GMC Truck Wiring Diagrams

You will have most everything there is to know about the TBI system used by GM on the P-30 chassis (circuit diagrams with wire colors and pinout, circuit descriptions, OBD1 code descriptions and how to see them, etc.).

kennyrodgers · February 27, 2016, 06:36 AM

Many thanks Dave. Got 'em.

kennyrodgers · February 29, 2016, 06:42 PM

Hi guys,
Update time once again.......
We got the o2 sensor changed out this morning thankfully., more about that later.
We spent most of our time troubleshooting the propane system, we went through as much of it as we could but still no joy. We've one last electromagnetic switch to test on the tank and if that's not the problem we're kinda stumped.
Again because of the limited time we had we only managed to check the main transmission electrical connector. It was basically full of transmission fluid so we cleaned it out as best we could. Due to the time we spent on the propane side we didn't manage to get out for another road test....i should get time later in the week all being well.

Sooooo, whilst we were trying to get the engine to run on propane after approx 2 to 3 minutes the ECU threw a code 45, running rich code as it turns out. Whilst this is a concern it's also a relief because at least we know the new sensor is working and the old one must not have been. Again we're slightly stumped due to the new CTS, Injectors and TBI rebuild.

I'm hoping this might be because the ECU has to relearn the fuel strategy but if not it gives up some pointers for where to look. We're still getting lots of black smoke when the engines cold so we're not quite there yet. The idle is still high but we didn't get chance to anything about that today.
I'll keep at it and for now as always will welcome any pointers you guys can offer.
Cheers for now,
Pete.

Rickf1985 · February 29, 2016, 07:49 PM

Disconnect the battery and let it set for a few hours with the headlights turned on to completely drain the keep alive memory. That way you know you are starting from a fresh slate. If still no joy you may need a new ECM. It may have been toasted in a jump start or a short in the system could have spiked it. The only real way to tell is a known good one. I realize this is not something you want to hear in a place where they are not just laying around in junkyards.

Starting from scratch you should not have any black smoke at idle since it will be running on the baseline ROM memory. If that got corrupted then you will need a new ECM.

kennyrodgers · March 01, 2016, 03:47 AM

Hi Rick,
Thanks for the suggestion and certainly something to think about.
I've just checked Rock Auto and the price isn't too concerning for a re manufactured AC Delco unit providing the one I would need isn't the most expensive one, sods law it would be though. That said however they all say I'll need no to change the Prom, if my ECU is toast would the Prom still be OK ?
I think I'm going to go for an ALDL adapter and either Tuner Pro or ALDLdroid so i can hook it up and getter a better idea of what's on. I'm hunting blind at the moment.
Whilst I'm here a question re the codes.
Would it throw a new "check engine light" code 45 every time the engine was run albeit after a few minutes of course....or would/should the check engine light stay on until I manually cleared it or if the problem went away on it's own.
The reason I ask is that it only showed the check engine light on one occasion. Also, my black smoke seems to clear once it's warmed up and I'm presuming in closed loop. Would the check engine light go out at that point on it's own.
Pretty rubbish way of describing things so hopefully you can understand what I mean.
Thanks again,
Pete.

SLEETH · March 01, 2016, 07:08 AM

I think you need to deal with one problem at a time
ie: getting the unit to run fine on wet fuel before switching it over to dry fuel
f.y.i. cel on all the time=hard code(failure) /cel intermittent=soft code=non hard code(failure)

Rickf1985 · March 01, 2016, 11:27 AM

The O2 sensor has to warm up before the system will go into closed loop and the ECM takes over control of the injector pulse width. If the exhaust is cleaning up to the point where the O2 sensor is switching back and forth consistently then you can feel good that the ECM is good. It is totally possible that someone had a chip in this thing before OR........ and this is a biggie, they may not have the correct prom in it! You would have to check the calibration numbers against a database to find that out. That is one I had not really thought about until just now. I agree with SLEETH, You need to work on the gasoline system first and get that in order and then work on the propane system. Or vice versa. I am not at all familiar how the propane system ties into the OBD computer so I will back out of that one. We have very little of that over here. If one of those programs you mentioned will show you the pids, or running data, that will tell you volumes about what is going on and what is wrong. It will not come right out and tell you most likely but given the data I can help you figure it out.

SLEETH · March 01, 2016, 03:29 PM

ive have done many propane & dual fuel conversions =was licensed contractor once upon a time
time to view the data stream (as per rick)

kennyrodgers · March 01, 2016, 07:23 PM

Cheers Guys,
Truth is I'm a bit stuck for time at the moment so as my buddy was over for the day on Monday I wanted to go through the propane side of things, checking wiring which was a joke to be frank, solenoids working etc etc whilst there was two of us

Up to now we've not had the engine fired on propane at all since it came back from the first annual test back in November. If you remember it mysteriously quit working after we parked her up for the work and up to now we're still not getting any gas up at the mixer. I've two things left to try. Firstly there's an electromagnetic switch on the tank valve. On checking it yesterday we found that it was permanently live and after speaking to a techie today found out that it should not be so, it should be switched via the ignition He thinks there's every chance that the coil would have burnt out in the switch as a result and if that's not the problem then the only thing left to try is a new propane system brain.....Think I'm going to need one when I'm done !!

I've ordered a Bluetooth adapter today from 1320 electronics in the U.S. It'll take at least a week to get here, maybe two but at least we'll have something to aim for once we can see what's what. It has a scan feature as well as the android monitoring app.
When you guys talk about hard and soft codes.....will a soft code go away if for example the ecu has been used to dumping fuel in but is now re learning due to the new o2 sensor. Forgive me if that's a dumb question but I'm not 100% sure how these ECU's work.
Thanks again all,
Pete.

SLEETH · March 01, 2016, 08:11 PM

soft code=stored in ecm memory=light off
hard code=stored in ecm memory= light on(all the time)=easer to find defective system
why not purchase a used snapon scan tool (used off of ebay)aka as the brick pn# mt2500(lots on there for sale)
with out a scan tool your just throwing darts at the bord