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

[kennyrodgers]

Hi Folks,
I'm hoping some of you guys Stateside can help me troubleshoot my 1994 454 TBI motor.
Not sure if a 94 constitutes a classic but here goes.
I bought my RV in early November as an inspection failure or M.O.T failure as we call it over here.
Please bear in mind for later that as gas is so expensive over here in the UK a lot of folks fit Liquid Petroleum Gas systems thereby cutting running costs practically in half, also she'd been sat for nearly seven years.
So, I bought the vehicle and had it trailered to the testing station where it failed on a number of minor things and then my friend drove it home for me, maybe 4 miles at most. He said it ran terrible of Petrol but when the LPG system was switched on it ran great.
Forward to last week and the LPG system has mysteriously stopped working (electrical fault somewhere) so this weekend, I took it for a retest, it passed btw, but had to get it the four miles there on petrol, i was hoping to get it there on LPG but alas.
She ran terribly, no power whatsoever and she struggled to get over 30mph,anything other than feather light throttle caused backfires. Anyway, test passed and I'm thinking the injectors might be fouled so I took the air filter of and sure enough, only the left side injector was passing fuel. On closer inspection I found it was just a bad connection, sorted that out and the right side injector is now working.
The problem now is that the engine is running worse than ever, very lumpy idle where it was smooth before and major misfires and constant backfires. Also there's dark smoke at the tailpipe and she smells very rich but not quite raw fuel.
The distributor cap and rotor are new by the way.
Any pointers you guys could give me would help greatly as I'm scratching my head now. I'm fairly competent mechanically but troubleshooting something like this has got me stumped.
Thanks in anticipation,
Pete.
UK.
i??

[GONMAD]

I believe that it;s an OBD1, have it put on a scanner for any codes for the problem. The TPS has to be set to an ohmage value. I have had this experience with a "DUMB" FI system & the throttle position sensor HAS to be set with an ohm meter to a value for that system. I usually switch back to a good manifold & carb assembly & just leave the wiring intact in the event I want to switch back. So far all the conversions have stayed on. Pretty much trouble free after that. Be sure to use a good fuel pressure regulator set to 5/7 lbs. & don't forget to hook up the return line as these pumps will burn up if it's blocked off. I use a HOLLEY regulator that has two output ports for the fuel, just use one for the return. Just my two cents. C YA! Gonmad 

[DaveVA78Chieftain]

I doubt if MOT will allow him to convert to a carb.

Yes OBD1 with TBI.  To read the codes:
With the key "ON” and the engine "OFF,” jumper ALDL terminal "B” to "A.” The "Service Engine Soon” light should flash Code 12 to indicate that the diagnostic system is working. Code 12 consists of "one flash” followed by a pause and then "two flashes.” The code will repeat for a total of three times and will continue to repeat if there are no other codes stored.

Download the 1991 Truck TBI Fuel and Emissions book from the Member area.  Should be close enough for troubleshooting the TBI system.  Has all the codes that can be generated (flashed).

Refer to page 3-9 (pdf page 53) for troubleshooting the codes.

[kennyrodgers]

Many thanks Guys.
Got the fuel manual from the members area and really appreciate you pointing me to it Dave, I didn't realise it was there.


I'll keep at it.

PS, I could legally convert to Carb but I think that would be a last resort but thanks for the suggestion.....let's see how things pan out.

[Rickf1985]

You say this sat for a long while and it runs good on lp so how old is the gasoline? I am thinking you have stale gas that has gummed up the injectors. Drain the tank and put in fresh gas along with something like Sea Foam and run it for a bit to get the cleaner through the system. I have found that if the Sea Foam is too concentrated it will cause smoke but will do no harm. Just run it through and then clean gas afterwards. You will need to do this before doing any other diagnosis if it had old gas in it.

[legomybago]

Sounds like a faulty O2 sensor to me. Read the codes.

[kennyrodgers]

Hi all,
Rick,
She's got maybe 30 gallons of fresh gasoline that was put in after the tank was emptied, there was very little in there to start with. I've fitted a new fuel filter and now both injectors are working and passing plenty of fuel. I've been down there today now that I know about the OBD1 codes and it's flashing a constant 12 code over and over and no other codes present.
I quickly checked today and with what little research i had chance to do I read that all fault codes will be cleared if you disconnect the battery for 20 seconds or more.
If this is the case I've lost my fault codes as i always disconnect both sets of batteries when she's parked for the day. If any of you guys can confirm this I'll go down again this week and run her up to temp and see what happens.
Thanks again for the help.
Pete.

[joev]

yep if you are disconnecting the battery it will reset the codes and you will need to start the engine up and run it for a while for the codes to show up again this could take up to 30 miles of driving or it will show up right away

[kennyrodgers]

Many thanks Joev.

[Rickf1985]

Yes, taking the cables off will delete the codes but keep in mind a couple things. OBDI is not a real code heavy system and also codes are only what the ECM sees. There are no codes for anything mechanical or anything outside of the OBD system, which is just about everything. A repeating code 12 is the code for the end of the list or no codes if that is all that shows. You say it passed MOT even running bad? That seems very odd. I am assuming they are doing an idle test only since you were saying that it was acting up on any kind of acceleration. How does it idle? With a sooty exhaust it should be setting a O2 sensor code. Probably 45. Or the sensor is not working which would be a 13. Another thing I can think of that would fit the way you say it feels when running is a worn EGR valve, try disconnecting the hose and plugging it at the EGR valve and see if that improves things. A weak EGR will make it run lean which can fool the O2 to give too rich of a mixture and it all goes to hell from there. D:oH! But at idle the EGR is off so it could pass emissions. Whatever you do, do NOT totally base your diagnosis on the codes you find. Use them as a guide but check other things also. It takes a combination of two variables to set a code but if there is a mechanical issue involved the computer has no way to interpret that so the code may or may not be accurate. OBDII is much better at the accuracy of the codes but the same applies, do not go straight for what the code is without verification through mechanical testing. You will save yourself a lot of money and time and hair this way.

Note, Here is a list of the GM codes.
http://www.gmtuners.com/OBD1_DTC.htm

[kennyrodgers]

Thanks again Rick.


I'm guessing it passed the emissions test because there was only one injector working at the time. The tester did comment that the hydro carbons were very low,almost zero at idle, now we know why i guess.
I should have mentioned this from the get go but the air injection system has been removed from this engine prior to me owning it along with the AC. Not sure if it's relevant to my issue or not.
Before i found the injector issue it idled nicely but was very sluggish indeed out on the road, 30 mph was about it. Now that i've got rhe second injector working the idle is lumpy and there's a definite misfire somewhere, also the dark smoke, not anything like a diesel but you can see it.
I'm not sure about the EGR vlave, I'll have to locate it and see what we can find with that.
Many thanks once again.
Pete.

[Rickf1985]

You may have the second injector working but I will bet it is not working right. It needs to be spraying a precise fine pattern and I will bet it is pissing instead. I will bet the code is 45 due to incomplete combustion because of a dirty injector. That is a low pressure fuel system (for fuel injection) and they used to make a kit that you could use to flush injector cleaner right into the line while it was running. I doubt you will find that anymore since the system is kind of dated. You are most likely going to need a new or rebuilt injector. The EGR will not give you black smoke at idle unless it is stuck open and the computer is trying to compensate but not likely since they usually go open loop at idle due to the O2 sensor cooling off. Since all of the other emissions stuff is gone you can get or make a block off plate for the EGR valve and get rid of that. The only downside is you may have to retard the timing a few degrees if it starts pinging due to no exhaust gas in the cylinder and it is now firing too hot and too early. The down and dirty EGR disconnect is to hammer the top of the EGR valve down so the pin is jammed into the hole and cannot open. I don't suggest doing that unless you know how. N:(

[TerryH]

Question, Rick:
From Pete's original post:

"Forward to last week and the LPG system has mysteriously stopped working (electrical fault somewhere) so this weekend, I took it for a retest, it passed btw, but had to get it the four miles there on petrol, i was hoping to get it there on LPG but alas."

My understanding is that many of the LPG systems for TBI incorporate a computer module that adjusts timing as required for the fuel selected - propane burns cooler, approximately 10% fewer BTU's created.
Would it be possible that this module may have failed "electrical fault somewhere" and the timing is considerably off? Runs rough, misfires, backfires.
Just wondering if it may either be or be contributing to the problems.

[Rickf1985]

Could be but I doubt it. Two totally different systems plus the timing for propane is advanced pretty far for gasoline. I am not really up on the dual fuel systems so I don't know much about the switching systems. I would think the OBD system is off for propane running. The O2 sensor would not be calibrated the same unless there are two sensors. Propane is usually injected under the carb, and in this case the throttle body, by an Imco mixer. I would bet it is a very basic system. Timing is probably not changed and the propane just uses the gasoline timing.

[kennyrodgers]

Hi Guys,
The LP system is of Australian origin, it sits in the somewhat modifies air filter housing. i doubt the timing has been altered as well because the fuel lines are directly above the bolt for the dizzy hold down tab.
Just to confirm then Rick, as the air injection system has been removed I can delete the EGR valve and blank it of, If so I can manage that OK, I have something at home that'll be perfect for the job.
A little more info.....I found the test history from a Gov't website and the last time she passed her MOT was 2007, no subsequent tests since. She did 600 miles that year and again, nothing since, My gut tells me that the motor hasn't run on gasoline at all since at least a year before that.
I took a couple of videos of the injectors, the first one is of the left one working on it's own and the second is when I got them both working. The left one before and after is firing a conical pattern with quite a lot of dripping from the centre. The right hand side that wasn't working looks to be making a nicer pattern without any dripping. If i can find some way of hosting them I'll get it done and post a link up.
I've a bunch of new parts inbound for the ignition side and a rebuild kit for the TBI, maybe I should add a couple of injectors to the list. The other option is to take them to the local injection specialist and get the cleaned and serviced.


Once again Guys, thanks very much for the help, it's very much appreciated.
Pete.

[kennyrodgers]

And a video link.
http://www.youtube.com/watch?v=00CnvhGl69Q


This is the horror that greeted me when I took the air cleaner of. No plastic connectors on the injectors and instant gasket covering everything. I think there might have been a fire in there at some point as the injectors are hard wired and joined to the wiring loom with the block connectors you can see.
Also, between the two fuel lines there's what appears to be a vacuum line that's been plugged, any ideas on what that one is ??
What do you think of the spray pattern then guys....not so good ??
Thanks again.

[Rickf1985]

I would definitely go for either new injectors or send them in for service. The one is really bad and the other is iffy. That whole area is really cruddy, almost like it was run for a long time without an air cleaner. The missing vacuum line would be for the evaporative emissions canisters if you have them or it would be for power brakes and I am pretty sure you have Hydroboost on that one. As far as the EGR, The EGR does not work with the AIR system together really. EGR was around before they started AIR and has stayed around to this day. The purpose of it is to feed a metered amount of exhaust gas into the intake charge to cool the combustion and by doing so it controls the oxides of nitrogen. You can disconnect it if they do not check it there in a visual test and if all they do is an idle test for emissions testing. The original timing calibration for the engine is set a few degrees ahead to compensate for the leaner charge due to the exhaust. You may find that it runs hotter and it may ping. you can either retard the timing a few degrees until the pinging stops or run premium gas. Depending on the amount of ethanol in your gasoline you may not have a pinging issue since ethanol causes the charge to run a bit cooler and it also has a higher octane rating. I noticed mine pinging on my last trip but I think I am gong to get a new distributor from Performance Distributors. http://performancedistributors.com/. I have not called them yet but they will set up a distributor for the application you are using. They set the curve you need so you do not have to screw with it. I have heard good things about them so I am going to give them a try.

[kennyrodgers]

Thanks again Rick, I'll look into options with the injectors.
I doubt I'll be able to find a UK supplier so I might order a set from over there and then also get the old ones refurbished over here.
going back to the EGR Valve,
Now that the AIR Injection has been removed is the EGR redundant. If not I think I'd like to keep it if just for the detonation issue. That said though I believe that once I have the LP side sorted out I'm going to have to back the timing some anyway....Just thinking out loud.
Thanks for the heads up about the distributor, I'll have a look into it.
Thanks again for now,
Pete.

[Rickf1985]

If all of the vacuum lines and controls have been removed the EGR may not even be hooked up. Take the line off and put your finger on it and rev the engine and hold it steady at high rpm and then let it drop to idle. You might feel a little vacuum as it is holding at high rpm or as it drops. Sometimes it is hard to feel and sometimes you can't feel it. It is also timed so it does not come in right away so as to keep the engine from stumbling right off idle. The best way to check it is with a vacuum gauge ted into the line and while driving. Not pleasant in one of these I can tell you! On the sdie of the air cleaner there should be a diagram of the vacuum hose routing for all of the emissions hoses. You should be able to tell from that if it is hooked up or not. That should also tell you about the mystery hose plugged on the throttle body.

Rick

[kennyrodgers]

OK Rick Cheers,
I shall investigate further,
Just contacted a guy in TX re the injectors, Dieseldawg he goes by. All being well there'll be a set winging they're way here soon.

[kennyrodgers]

Just a little update,
No news yet on the running side of things but the shopping list has been quite extensive,
En route or already in are....
80lb injectors from Bigdawg Diesel in TX. The 94 runs higher fuel pressure than previous years and I'm assured that my RV will "run like a champ" once these are fitted. I've also ordered a TBI rebuild Kit.
Sensor wise...ECT, MAP, and o2 sensors
Ignition side...Control Module, Cap, Rotor, Plugs and Leads.
I've also managed to find a pretty nifty OBD1 Bluetooth monitoring system and an Android App for real time monitoring.


I've also read that going down the Carb route ( if all this fails ) is a bit more challenging than I first thought. i have a 4l80E Trans that needs the ECM to shift. There's always something....
I won't have everything in for a couple of weeks so the plan is to wait till it all gets here then start with the Throttle Body and Injectors then take it from there.
I'll keep you all posted how we get on.
cheers for now.

[MotorPro]

Why not find the problem instead of throwing money at it?

[Rickf1985]

The 80lb. injectors will make it run like a champ but you will have to learn to keep your foot off the gas pedal or you can expect mileage in the 4-6 range! They are high performance injectors and are really not needed in a motor home. The transmission shift issue could be overcome with a stand alone shift controller. I agree that you are throwing a LOT of money at this thing before getting it running correctly. Have you done a compression test on it yet?

[kennyrodgers]

Hi Rick,
Thanks for dropping by..
They are the correct injectors for my year having the higher pressure from the pump. I think the 80lb flow was by way of reassurance more than anything else.
The goal in all this is to get it running good on gasoline but the vast majority of mileage will be done on Propane. As far as the cost up to now, it's not too bad to be honest. I don't mind throwing a couple of hundred bucks at it and the peace of mind will be worth it I feel as well. It was in the long term plan to change the ignition parts but for what it cost I thought I may as well get it done now.
No compression test up to now though.

[Rickf1985]

I don't think your cost per mile will be much different between propane and gasoline. The BTU value of propane is much lower than gasoline so you need a lot more propane to get the same amount of power. Do you have a lot of propane filling stations over there?