Bricky EFI question

[RenoHuskerDu]

It's a friend's 1990 F150 with the 300 six. It's clearly too rich at idle and low speed, but cleans up at higher RPM. We have one gasser parts truck with a 351. We could swap in parts off that truck.

We're not too familiar with these early EFI systems. I'm scratchin my head trying to remember 30 years ago. One of my sons is a full-time wrench and has never had an EFI vehicle in for service or repair (also never seen points and condenser in his shop, so I had to teach him).

As I recall, on these early EFI  systems it's based on a simple airflow sensor, just a flap, with corrections for coolant temp, ambient temp, and atmospheric pressure. I don't recall them having closed loop or O2 sensor.

I guess I'll just start ohm testing the various components for dead shorts or open, once I get info on specs. Also, inspect the air flow sensor visually and put a DMM on its output to see if it's lumpy instead of a nice curve. I have this question out on FTE too, but am doubtful I'll find much help.

[RenoHuskerDu]

I actually got a few responses on FTE. But there seems to be confusion about OBD on a 1990. Several advised me to read codes. I'll take a closer look under the dash tonight. I didn't think Ford adopted OBD that early.

Another thing that surprised me is that this early EFI has no way of measuring intake mass. No flap, nothing. Just stored maps used to set injection volumes under varying conditions. Live and learn.

[Gary Lewis]

I actually got a few responses on FTE. But there seems to be confusion about OBD on a 1990. Several advised me to read codes. I'll take a closer look under the dash tonight. I didn't think Ford adopted OBD that early.

Another thing that surprised me is that this early EFI has no way of measuring intake mass. No flap, nothing. Just stored maps used to set injection volumes under varying conditions. Live and learn.

If there's no mass air flow sensor then the truck has EEC-IV with what is called speed density. In other words, they know how many cubic inches the engine has, what cam it has, how big the valves are, and what exhaust system is on it. So they know how much air it ingests with any given throttle opening. Assuming, of course, that none of that has been changed.

Most EEC-IV systems don't have an OBD-II port, and I believe the few that do have don't have a fully functional OBD-II interface. But I'm not sure on that.

I'm going to ping Bill Vose as he may know about this.

[grumpin]

If there's no mass air flow sensor then the truck has EEC-IV with what is called speed density. In other words, they know how many cubic inches the engine has, what cam it has, how big the valves are, and what exhaust system is on it. So they know how much air it ingests with any given throttle opening. Assuming, of course, that none of that has been changed.

Most EEC-IV systems don't have an OBD-II port, and I believe the few that do have don't have a fully functional OBD-II interface. But I'm not sure on that.

I'm going to ping Bill Vose as he may know about this.

Here’s what I use on my 92 Bronco. I like it, it works good.

https://www.innova.com/collections/obd1-tools/products/digital-ford-code-reader-1981-1995-3145

[85lebaront2]

Since I was tagged (I guess that means I'm IT), 1990 is an EEC-IV system, the diagnostic connector is on the back side of the air filter bracket and is two separate plugs, a large odd shaped multi-pin and a single pin. An OBD-II (parts store) tester will not work on it and if I remember correctly 1990 will not give live data. If the 6 uses the same locations as the V8s the MAP sensor will be on top of the HVAC casing. Make sure the vacuum line isn't cracked or collapsed as it will make it rich, also check the line from the pressure regulator for liquid gas inside which indicates a bad regulator.

Here is a way to retrieve codes without a scan tool on Ford OBD-1 systems:https://www.fordtruckzone.com/threads/how-to-retrieve-trouble-codes-on-your-eec-iv-system-without-using-a-code-scanner.659319/

It gives you a way to get both sets KOEO and KOER (engine off or engine running). ECT can make it pig rich, but it won't usually clear up at higher rpm. Good luck, and ping me if you need more on it.

[Gary Lewis]

Since I was tagged (I guess that means I'm IT), 1990 is an EEC-IV system, the diagnostic connector is on the back side of the air filter bracket and is two separate plugs, a large odd shaped multi-pin and a single pin. An OBD-II (parts store) tester will not work on it and if I remember correctly 1990 will not give live data. If the 6 uses the same locations as the V8s the MAP sensor will be on top of the HVAC casing. Make sure the vacuum line isn't cracked or collapsed as it will make it rich, also check the line from the pressure regulator for liquid gas inside which indicates a bad regulator.

Here is a way to retrieve codes without a scan tool on Ford OBD-1 systems:https://www.fordtruckzone.com/threads/how-to-retrieve-trouble-codes-on-your-eec-iv-system-without-using-a-code-scanner.659319/

It gives you a way to get both sets KOEO and KOER (engine off or engine running). ECT can make it pig rich, but it won't usually clear up at higher rpm. Good luck, and ping me if you need more on it.

Thanks, Bill. I knew you'd know.

[85lebaront2]

Thanks, Bill. I knew you'd know.

You might want to save that link as it will work on the 1985/86 EFI 302s, main difference is test connector and MAP sensor are behind the battery.

 

[ArdWrknTrk]

If there's no mass air flow sensor then the truck has EEC-IV with what is called speed density. In other words, they know how many cubic inches the engine has, what cam it has, how big the valves are, and what exhaust system is on it. So they know how much air it ingests with any given throttle opening. Assuming, of course, that none of that has been changed.

Most EEC-IV systems don't have an OBD-II port, and I believe the few that do have don't have a fully functional OBD-II interface. But I'm not sure on that.

I'm going to ping Bill Vose as he may know about this.

Yes, OBD-1 is not only far different than OBD-II, the codes are not standardized across manufacturers, so prior to 1996 it was specialized.

I was going to point out how to pull codes by grounding with a paperclip while counting flashes of the check engine light but I see that's been covered.

One thing I will add to what Bill has said is to address numerically lower codes first, as fixing 3 can resolve 11 but not the other way around.

[85lebaront2]

Yes, OBD-1 is not only far different than OBD-II, the codes are not standardized across manufacturers, so prior to 1996 it was specialized.

I was going to point out how to pull codes by grounding with a paperclip while counting flashes of the check engine light but I see that's been covered.

One thing I will add to what Bill has said is to address numerically lower codes first, as fixing 3 can resolve 11 but not the other way around.

Very true Jim, and Ford started 3 digit codes on the later OBD-I vehicles.

[RenoHuskerDu]

You might want to save that link as it will work on the 1985/86 EFI 302s, main difference is test connector and MAP sensor are behind the battery.

Thank you Sir. The gentleman is bringing his pickup over this evening and we'll have a go at it.

My son did find a Ford-specific OBD1 reader at the repair shop where he works, left by the PO, who retired. We'll see if that plugs in.