1990 F250 Lariat XLT; engine 7.5L, 460 big block
I have had this old truck for about 5 years. It’s been pretty solid except… and I have NEVER figured out why… after driving for about 25 minutes straight, the check engine light comes on. A few years ago it would NOT start again if you shut it off until some time passed… but I had someone help me try and figure it out and we noticed the battery terminal was loose. Since then, I can get it to start after the check engine light comes on, but it’s a harder start. I’ve been through a few starters over these last 5 years. New solenoid, battery is a few years old, new alternator a few years ago, new plugs and wires a couple years ago.
I canNOT figure out this check engine light issue and WHY it’s only after driving for 25 minutes. ANY help you can offer? I’m at a total loss.
Rich
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There is no code checking access point. It’s too old for that.
You are correct that you cannot use a modern scan tool, but 1980-1995 Ford vehicles are equipped with OBD1 diagnostics. Specialized scanners or a paperclip (or jumper wire) can be used to read the codes. Here is another link and a video showing how to do it:
https://www.youtube.com/watch?v=-YYQKssOEOs
Okay! I’m with you now.
WOW… for 5 years I’ve been trying to figure this out and never knew there was a code reader that I could buy. Just bought one and used it to test my truck. Here’s what I found:
CYL — 8
R — 41
R — 77
R — 74
R — 65
O — 11
C — 32
C — 41
C — 67
O is the key on engine off test
C is the continuous memory code
R is the key on engine running test
NOW… to figure out what it all means.
Okay… I’m learning… read the obd1 manual and checked codes than rescanned. Here are my final codes:
O—11
C—32, 41, 67
R—41, 73
11 is "system pass" - I guess that means the ECU is working.
Other than that , it looks like you have an EGR sensor problem, a lean condition problem, a problem with neutral/drive switch (neutral safety switch?), and a problem with the throttle position sensor.
So… it’s a 1990… just bad sensors or I have a bigger problem? I think my rear tank has a leak so, I don’t use it (don’t need it), but other than that it drives fine (until it trips the check engine light). It also smells “hot” after 25 minutes or so of driving. It smelled hot during these tests today too. Shall I start with replacing sensors or is there some other direction to take?
Probably the lean condition should be addressed. (Vacuum leak possibly.) Taken verbatim the codes indicate there are sensors that should be replaced. However I have no experience with that engine so don't know what else might trigger those codes aside from maybe wiring problems. On a 32-year-old vehicle it's certainly worth checking wiring and connectors before throwing parts at it.
Checked for vacuum leaks today. Used carb cleaner and sprayed all areas that might present a leak. Nothing. I guess there could be an exhaust leak somewhere, but most of those issues have been remedied. I thought about trying the EGR sensor next and maybe the throttle sensor? Not difficult to change and could be the culprit (other videos I’ve watched mentioned those sensors being a problem with this engine).
Sometimes on these older vehicles, the check engine light would be hooked to the odometer and come on automatically after a specified mileage. It didn't mean that anything was wrong, it was just a reminder to check the 02 sensor. On my truck (Toyota) there is a small box way up under the dashboard with a switch in it. My light comes on every 30,000 miles. I have to reach up and move the switch to the opposite side and the light goes off for another 30K miles. Your truck may have this feature. Sometimes, you just reset it by disconnecting the battery.
There is no code checking access point. It’s too old for that.
You should find out what the light is trying to tell you. Use the paperclip method in the link Chuck posted.
In case this gets missed… I did answer a response above (I wasn’t prepared for you guys to be to quick and thorough!
After buying an OBD1 code reader (never knew these existed before today) and doing multiple tests because I didn’t finish reading the “how to” of testing, I came up with these codes:
O—11 (key on engine off)
C—32, 41, 67 (continuous memory)
R—41, 73 (key on engine running)
Now, to figure out what’s wrong based on these codes and if I can fix the issues. This is the closest I’ve come to figuring this out in the past 5 years of asking/checking/wondering…
You mentioned a possible vacuum leak. Have you checked the condition of the gas cap?
The gas cap? It’s fine. I mean, I don’t see any issues. I checked the engine compartment for vacuum leaks (spraying carb cleaner on hoses/connections and never noticed ANY increase in idle. I watched a few videos on these engines/other engines where this test worked well and was noticeable. Gas cap fits well, looks good. HOWEVER… I think I have a leak in the rear tank (it has a front and a rear tank). I haven’t used that rear tank in YEARS. I noticed it leaking a few years ago after I had added gas. Stopped using it since because I don’t need it…
I am changing the EGR valve and the EGR sensor as well as the throttle position sensor. Those two things were noted based on the code explanations.
@RSaunders Well, you and others here know infinitely more about cars than I do.
I receive here much more than I contribute. But as I searched for a possible cause for your car's problem, the issue of the gas cap was mentioned multiple times in regards to the EVAP system and as the possible cause of a motor running lean with the symptoms of poor idle, loss of performance and even stalling and can certainly produce a code.
So as others here delved deep into the internals of the engine, my novice self thought that perhaps it was something simple like the gas cap that was being overlooked. As Solomon wrote, "It's the little foxes that ruin the vine."
But I certainly hope that you discover the problem and are successful with the solution. And when you do, I hope that you will post it so that those who have offered their knowledge and advice as well as the 75 others who have viewed your question/topic will gain some automotive knowledge. Thanks.