As the engine is running fine - starts, stops, has plenty of power - and the only thing that seems to be off is these two codes, is it still likely to be the engine control module that's going bad?
We've changed the fuel pump relay and the pump is still running constantly when the ignition key is turned on.
Just asking as never had one of these vehicles before and it's all new to us. All advice appreciated!

 

How right you were! We went through Rock Auto's online return form, and sent them a photo of the box that arrived, and what was in it, and they called yesterday to say that the wrong sensor had been put in the box at the factory. So they're sending us the correct sensor free of charge! Nice to find a company that will accept responsibility for mistakes.

 

Slight chance the fuel pump relay socket has corrosion built up on the wires, causing the coil to energize whenever the EEC relay is energized. That's a stretch.

 

Well, we unplugged the engine control module connector and cleaned the contacts, plugged it back in - and now whenever we switch over to LPG, the CHECK ENGINE light comes on on the dash. After a couple of switches back and forth, it also started coming on when driving on petrol. Not exactly the result we had in mind! LOL

Re: the vacuum pipes, we have had a good look in the engine bay and there are definitely exhaust fumes escaping from the back of one of the vacuum pipes that runs over the top of the engine block (the t-piece that runs over the RHS of the block). The piping is very brittle-feeling, so there may be a crack there.

 

Another LPG conversion truck....bugger!

Since the CEL is on, check for codes.

 

Well, we did the codes again -
pretty much the same as before:

KOEO
95 - fuel pump secondary circuit fault
41 - o2 sensor pooped
96 - high speed fuel pump relay open

and as a bonus: 33 - EGR valve fault/not closing properly - we didn't get that code before!

KOER
41 - o2 sensor pooped
74 - BOO switch fault/not activated

We didn't know if the 1990 engine had SEFI, so we tried the cylinder test but it didn't seem to work - I assume that means the engine does NOT have sequential electronic fuel ignition, but was still on the batch-firing system.

 

You are getting erroneous codes because the clock is not running inside the PCM computer. That is why you are getting the O2 sensor codes, BOO code and the fuel pump is running as it can not time out with the clock not running.

You have no high speed fuel pump relay in a 1990 truck, only the fuel pump relay.

After the computer is replaced the codes should all be gone.

It does sound like you may also have a bad fuel pressure regulator as that is what is indicated when you have fuel in the vacuum line from it.

 

Thank you for the information! Ouch. But it would explain all the weird results.
We're looking for a replacement unit as all the UK-based American auto part suppliers want not just an arm and a leg for it but the full set of limbs!
We're looking on Rock Auto and Summit Racing, both of which export to the UK. Anything we should look out for - brands to avoid etc? It's not the kind of thing we want to have to import twice!

What numbers should there be on the unit behind the kick panel? Just so we know what we're looking for. And, as the vehicle is still very much driveable, are the numbers readable with the unit still fitted, while we wait for the new one to arrive?

Cheers,
Rob

 

I was trying to head the OP in that direction before based on the fuel pump always running. But I also tossed a few other causes to verify before throwing in the towel.

 

Later model trucks have a Calibration sticker on the b-pillar/door jamb. It looks something like this:


Post yours, we can decode it for what computer you need.


You can also pull out the computer (PCM) to get the numbers.

For reference: Fuel Injection Technical Library » EEC Program Codes

 

I'd love to post the picture I just took but I haven't found a way of doing it yet!

The data is as follows:

CALIBRATION
ETALONNAGE FORD

0-98A-R05 FOAE-6E061-EEL

Thanks for the help guys!

Rob

 

Rob,

You can email me the photo at the email address at the bottom of this post and I will post it for you.
CALIBRATION 0-98A-R05 goes with parts list #67.
Parts list #67 says that your engineering drawing number that is on the PCM Computer is F0TE-12A650-ATA.

This is the number F0TE-12A650-ATA, that everybody goes by except Ford.
And Ford goes by the Ford part number and it is F0TZ-12A650-ATA.

There was another number in the parts list #67, F2PZ-12A650-AXA but that is a 1992 part number and it may be an updated part number or a superseded part number.

 

Thanks very much for looking that up for us, I've been going round in circles trying to find out how to decode the calibration number!
Have emailed you the photo of the calibration sticker.
Any brands preferable or to avoid?
Cheers,
Rob

 

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The calibration number does not decode.

You have to have an index that tells you what part list number that the calibration number points to.
Then you go to the part list number and the parts list will have all the part numbers and engineering drawing numbers for the truck that has that calibration number.