obd(koeo self test) Dave R

ranger40 · Aug 20, 2007

I saw a post yesterday Where Dave R. mentioned that there was
a big difference between no codes and nothing at all showing on the
cel(no flashes at all). I was running the test on my 88 2.3 and i grounded
the st1 terminal and turned the key on and the only lights i saw were the
oil and battery-no cel at any time. - truck will not start btw, was running a little rough at idle but otherwise fine driving to work-upon leaving work it
cranks but doesn't seem to fire. fuel pump and filter replaced 1 year ago.
thanks for any info,

r, john

Dave R · Aug 21, 2007

OK, perhaps this is a stupid question, some days I'm good for those, BUT, are you sure the CEL works at all? When you turn the key to run, but don't start the vehicle, the CEL should turn on. Some of the older trucks weren't wired for a CEL, don't ask me but there have been enough guys reporting this for me to be a believer. Do you have the EEC test port under the hood? If so, you can pick up a cheap OBD-I code reader from WallyWorld for about $20.

I'm guessing that your '88 is EFI w/ a distributor. If you have no spark, then first remove the distributor cap and double check that the dist shaft is turning. If it is turning, then there is about a 85% probability that your TFI module, gray plastic rectangle on the side of the dist., has failed.

ranger40 · Aug 22, 2007

Truck does have a distributor, efi, and a good spark. My mistake on the cel -
it's not wired in - i was trying to do the koeo self test per a pub i found
here or somewhere a while back where you ground the st1 terminal and count
the sequence of flashes. oh well. I'm thinking since it cranks good it might
be a fuel issue - filter and pump(hp) replaced a year ago, but maybe the injectors might be clogged? And incidently, Chiltons says the press relief for the fuel system is just downstream of the filter, and i cannot find a schrader
or any type of valve anywhere on the system. Is it maybe hidden behind
the bracket on the hp pump? Or is there some other relatively safe way
to bleed this thing and/or check gas feed without tearing the injector rail
out? Thanks again for any info,

r, john

Wicked_Sludge · Aug 22, 2007

injectors dont just suddenly get plugged. and it should still cough and sputter no matter how plugged they may be. im going with fuel delivery problems. check all relays, fuses, and both pumps (even the "new" one, a year is more then enough time for a pump to go out).

the schrader valve should be on the fuel rail itself.

an easy way to confirm a fuel deliver problem is to spray some ether in the intake and start the truck. if it runs then dies, its undoubtedly a fuel problem.

ranger40 · Aug 23, 2007

Found schrader, and appears to not be under any press at all - i cranked the engine a bit
and still no spray - i checked the only related fuse i could find and it's ok. The book doesn't show where the fuel relay is though, any ideas where it might be located?
I'm assuming i can check the output with key on and it should be 12v before i condemn
the pump?

Wicked_Sludge · Aug 24, 2007

not sure if '88 has the underhood fuse box or not. if so then the relay is in there. if not then im not sure where ford stuck it.

Dave R · Aug 24, 2007

Do you hear the fuel pump running while you turn the key to on? It will run for about 1-2 seconds to prime the system. If not, then the next upstream, electrically speaking, is the crash switch. It's usually under the dash right about where the left foot of someone sitting in the passenger's seat would normally be.

Check to make sure the switch hasn't tripped. If it's good then you can pull the electrical connection and jumper 12V+ to the wire and see if that turns on the pump. If it does then it's most likely your FP relay, or wiring. If jumping the connection doesn't turn on the pump then it's either a bad pump or chassis wiring near/to the pump.

ranger40 · Aug 24, 2007

well, i thought maybe if everything else was ok i could check autozone for the relay
location, so i went ahead and checked for power at the hp pump. no power there so
i then checked the crash switch again-which was actually the very first thing i had
checked for tripping- but it dawned on me that i could put 12v to it and see what happens per Daves' suggestion. When i pulled the connector, i noticed one side of the
little thing was melted/warped (slightly) right. So i snipped it out and just tied the wires
together(no crash protection now) . I could hear the pump now- truck started
immediately and problem for today apparently fixed. Thank you to Dave and Wicked
Sludge for the help on this with their time and knowledge,

r, john

Dave R · Aug 25, 2007

I wouldn't be too concerned about the lack of crash protection but I'd be wondering why the pump/s were pulling enough current to damage the switch/connector.

ranger40 · Aug 25, 2007

Well, i Thought it would probably be a good idea to go ahead and check all the
wiring in the fuel circuit asap-maybe tomorrow.... btw, i would like to add as what
i thought was the likelyhood that the burned connector was the source of the problem
due to a looseness either inside it or the female end on the switch. That could cause the
high current draw-there was only the localized melted plastic - the next connector at the hp pump was fine as was the wiring between- but i still plan to check further that
there's not something else amiss -

r, john

Dave R · Aug 26, 2007

A loose/poor connection in the fuel circuit will cause some interesting localized heating. I found that one out as well. Though the bad connection on mine was the pump ground wire to terminal post connection on the underside of the fuel pump assembly (inside the fuel tank).

scotts90ranger · Aug 28, 2007

that's a good place for a short...

jubangy · Aug 30, 2007

I had a similar issue on my old 89 ford bronco 2, and I thought it was the inertia switch as well as it was alittle burned looking. I ran a hot wire to bypass it and all that did was get the pump running for close to 3 days. Then the pump died for good. If the pump is junk at least on mine the relay wouldn't even kick in, once I changed the pump I wired things back to the way they were and all was well right up until I sold the brono. Just be careful.

Dave R · Aug 30, 2007

scotts90ranger said:
that's a good place for a short...

Actually it's not as bad as it sounds, there isn't enough oxygen in the fuel tank to support combustion, even if there was a spark.

Wicked_Sludge · Aug 30, 2007

Dave R said:
Though the bad connection on mine was the pump ground wire to terminal post connection on the underside of the fuel pump assembly (inside the fuel tank).

i had one of those too. but mine was the hot lead to the pump.

oxygen or no...it still didnt give me a "warm fuzzy feeling".

obd(koeo self test) Dave R

New Member

New Member

New Member

New Member

New Member

New Member

New Member

New Member

New Member

New Member

New Member

Well-Known Member

New Member

New Member

New Member

Sponsored Ad

Sponsored Ad

Member & Vendor Upgrades

Truck of The Month

Recently Featured

Follow TRS On Instagram

TRS Events

25th Anniversary Sponsors

Check Out The TRS Store

Sponsored Ad

Sponsored Ad

Sponsored Ad

Amazon Deals