Code 90

[92exp4x4]

So I have a rather interesting situation. Today I went to troubleshoot an issue with my Navajo. It's been running crappy for a while and I haven't played with it seriously until today. The truck would miss and seemingly load up. When it would drop cylinders I figured it was a fuel issue.

Well, today I threw a pressure gauge and my scanner on it and got some interesting results. Fuel pressure is right where it should be at 40 psi. KOEO 111, system pass. KOER codes are 157 and 998. Along with these it set a 90. Now as far as I know, 2 and 3 digit codes are not supposed to show together. It's either/or as 2 digit codes were used in the earlier generation of EEC 4 Has anyone had this situation on a 93-94 EEC 4 system? My truck is a 94.

The 157 is MAF, the 998 is PCM in limp mode, which makes sense. The only thing I can find about a code 90 is for system pass for the cylinder balance test. I didn't run that test so it intrigues me as to why I got this result. Does the KOER test automatically do a cylinder balance test in it's check? I can't see this being the case. Anyone had similar results? As for my truck it's getting a new MAF sensor and a little love as I haven't run it since May of 2019.

 

[CreepingNet]

Sounds a lot like what I had that lead me to re-capping my computer and replacing my MAF sensor recently. I had a 117, 122, 157, 513, 998 - 117, 122, and 157 are all below minimum voltage codes, and 513 is a voltage fault in the EEC, and 998 is EEC Hard Fault. Based on your codes, I'd check and maybe the MAF First, then pull the computer and look for leaky caps. If it's the EEC-IV then you probably just have one leaky cap that's corroeded off the board instead of 2-3 like I had.

 

[ChildIdenticant]

If you do open up your eec/ecu/pcm, take a pic or two please. After seeing CreepingNet's ecu, and then investigating further, these should definitely be suspect and least inspected for preventative maintenance. I opened mine up just as a matter of knowing it was done. Fortunately my nichicons tested fine w 0 leakage.( slightly different board layout btw on my 94).

addressing dtc 90 , it isn't listed in my chilton as a valid code but by

EEC-IV 2 and 3 digit trouble codes.

Here is a link to a list of 2, and 3 digit trouble codes, and troubleshooting information: Ford OBD/OBD2 Codes – TroubleCodes.net Here is a list of EEC-IV codes: 2 Digit Codes 11 System OK 12 Idle Speed Control motor or Air Bypass not controlling idle properly (generally idle...

www.explorerforum.com

:
90 SERIES FUEL/AIR INJECTION CODES ON VEHICLES WITH DUAL OXYGEN SENSORS REFER TO THE LEFT OR FRONT SENSOR. EXCEPT: 1984-1988 3.8L ENGINES: RIGHT SENSOR




theres no solution provided at the end but might want to glance at Trouble codes-Need Help - Ford Truck Enthusiasts Forums

 

[92exp4x4]

Sounds a lot like what I had that lead me to re-capping my computer and replacing my MAF sensor recently. I had a 117, 122, 157, 513, 998 - 117, 122, and 157 are all below minimum voltage codes, and 513 is a voltage fault in the EEC, and 998 is EEC Hard Fault. Based on your codes, I'd check and maybe the MAF First, then pull the computer and look for leaky caps. If it's the EEC-IV then you probably just have one leaky cap that's corroeded off the board instead of 2-3 like I had.

In the back of my mind, I figured I might be pulling the computer and taking a look inside. There has been a lot of PCM related threads on here the last few weeks. I ordered a new MAF last night, I'll throw it in and see what happens.

Thanks for the input!

 

[92exp4x4]

If you do open up your eec/ecu/pcm, take a pic or two please. After seeing CreepingNet's ecu, and then investigating further, these should definitely be suspect and least inspected for preventative maintenance. I opened mine up just as a matter of knowing it was done. Fortunately my nichicons tested fine w 0 leakage.( slightly different board layout btw on my 94).

addressing dtc 90 , it isn't listed in my chilton as a valid code but by

EEC-IV 2 and 3 digit trouble codes.

Here is a link to a list of 2, and 3 digit trouble codes, and troubleshooting information: Ford OBD/OBD2 Codes – TroubleCodes.net Here is a list of EEC-IV codes: 2 Digit Codes 11 System OK 12 Idle Speed Control motor or Air Bypass not controlling idle properly (generally idle...

www.explorerforum.com

:
90 SERIES FUEL/AIR INJECTION CODES ON VEHICLES WITH DUAL OXYGEN SENSORS REFER TO THE LEFT OR FRONT SENSOR. EXCEPT: 1984-1988 3.8L ENGINES: RIGHT SENSOR




theres no solution provided at the end but might want to glance at Trouble codes-Need Help - Ford Truck Enthusiasts Forums

I will definitely take some pics. I may even open the computer while I'm waiting on the MAF to arrive just too see what's inside. I haven't had one apart before.

I appreciate the code info. I was unable to find any info in my Ford service material for the 94 model year. I'm thinking the 90 is an erroneous code because of something else going on, like leaky caps. I'm nearly positive that a 3 digit system should never set a 2 digit code. Maybe there are 2 digit internal codes for production and they are not published to the public. Or maybe my PCM is getting Alzheimer's!

 

[92exp4x4]

I decided to mess with this today and sure enough, 3 blown capacitors. I'm amazed the thing ran at all. I think this one will probably be to too far gone to repair. There is a lot of damage to the neighboring circuits. I also found out the manufacturer for my particular board was Motorola. Their logo is imprinted near the part # on the board and on the processor.

So there it is. I ruled out the MAF, by robbing one of my other trucks and trying it. I dunno why I just didn't do that before. Turns out the Navajo is a 93 and not a 94 like I previously thought. Mine lacks EGR and and cam sensing.

 

[ChildIdenticant]

Disgusting. I wonder if that coating is a damage multiplier. Looks like it kinda seals in the rot. Thanks for sharing. Should make a sticky/notice to advise checking all 1stgen ecu's as it's an age matter not wear matter.

 

[92exp4x4]

Disgusting. I wonder if that coating is a damage multiplier. Looks like it kinda seals in the rot. Thanks for sharing. Should make a sticky/notice to advise checking all 1stgen ecu's as it's an age matter not wear matter.

I agree with that. The coating might have helped it keep out moisture, but it does seem to hold in cap leakage. These vehicles just were never meant to last this long. It really makes you wonder about the newer cars and where they will be when they are 30 years old.

 

[CreepingNet]

I'll second on the coating keeping the electrolyte leaked out of the caps on the board making it worse. That's how my 93 was. I just peeled it off and left it off. Lucky for us the computer is in the cab and not the engine compartment, so it's not as exposed to the elements as they are in the Ranger. The worst on mine was that one next to the CPU by the tan tantulum cap, that entire grounding pad was shot until I scrubbed it with tools till what was left of the copper showed up to solder to. The one in the pic here is nowhere near as messed up as mine was.

IMHO if $0.75 worth of capacitors is all that's wrong, that's pretty darn good for a classic 30 year old SUV. I'll take that any day over any other issue. Since I fixed mine it's been running like a brand new truck. I read somewhere here 10-20 years ago an engineer or a few from Ford got on and shared the story of the UN46 platform and I recall one saying something to the effect of of the only real problem with the 1st generation Explorer is that they were built "too good" and few people bought new ones for a very long time after they got one. I wish I could find that post again, it was interesting.

 

[Mbrooks420]

If it weren’t for the sealant the boards would fail much faster than this in humid areas. 30 years old for an automotive environment computer isn’t any shame.

 

[92exp4x4]

I agree that the explorer is built too well. They are extremely rugged, almost like a modern day model T. They use all the best of the half ton parts bins in a compact package. The cologne v6 had nearly 30 years of development by 1991. Even the A4LD, which is a weak point, isn't horrible and will last if treated properly. I've really abused one of mine... Somehow it still crawls along.

Any electronics that spend thier life essentially outside for 30 years with no faults is really something. With that said, I've always had Motorola phones. I find it very cool that the PCM wears the moto icon on its components! It is very humid and moist where I live in northern KY. In the spring, there will be condensation running down the inside of windows of cars when the temperature changes. It happens every year, and it sucks. The coating on the PCM definitely helped it survive here this long.

Capacitors only last so long, hell ignition condensers are replaced at tune up time on older cars with points. They are basically the same thing. The fact that these have lasted this long is kind of amazing really. Ford never intended these to be here being used daily in any quantity by now. The first gens just happen to retain many of the "rebuild able" abilities of older cars with simplified new car era tech. I'm just glad that these units can be fairly easily repaired. The top right cap on mine pretty much ate up all the traces below it. This PCM will likely be junk, but I am going to be buying some capacitors and I'll be doing some inspections of my other trucks to catch this before more damage happens.