longterm sustainability of vehicle electronics

As my '93 XJ is approaching it's 30th birthday in a couple of years, I have been thinking about the long term sustainability of the electronics onboard. What do I do if my electronics fail? My 4.0L has two fuel systems, the original MPI gasoline and an aftermarket propane system that was fitted twenty years ago. My goal is to get another 10 to 15 years from an engine rebuild assuming gasoline or propane is still available. A system that can also run on CNG is useful if propane availability reduces further were I live.

My propane system ECU is fairly simple to replace if it dies. It is no longer in production, but more fuel efficient systems are available now and they usually just need a timing source from ignition or cps and an oxygen sensor to run. Injector emulators are switched into the MPI circuit to prevent running on both fuels simultaneously.

However, my factory fitted ECU is more of a problem. Fortunately, my Jeep is pre-OBD2 so local emissions testing is based solely on what comes out of the exhaust. Perhaps I could replace it with a stand alone system like a MegaSquirt ?

My engine has a distributor ignition, but new stand alone systems like the MegaSquirt MS3-Pro can support coil-on-plug and wasted spark ignition. I am thinking that perhaps I could eliminate the distributor when rebuilding the engine and go to full electronic ignition using either the factory 2000+ coil packs or AEM Smart Coils with a stand alone system. The advantage of doing this is that my 2001 already has distributorless ignition so the same stand alone electronics system could be used on that too at a later date.

My AW4 is the older style with the separate transmission control module. Electronics replacement here could be NiftyShifter, or CompuShift.

ABS has already been junked. Is there anything else I have missed?

Has anyone already got to this point with a Renix system?

i got a 1990 xj, my newest car. no problem finding new or used injection sensors. the ecu often lasts forever. no worries here. I easily maintain an older injected car, a 1972 porsche, no problems with getting parts.

sure stock up on spares new or used for fast repairs.

they made a boat load of these jeeps, many parts!

Viper (or V6 minivan) coil is another option for coil rail replacement.

I had to replace the ECU on my 92 once, but I suspect the "potting" material that covered the circuitry had degraded and allowed water infiltration (started having problems with no tach signal after water crossing, eventually no start at all). If it's possible to open the shell, you could look for cracking in that stuff and "repair" it with an electronics-safe version of RTV Silicone (I did this some years back on a mid-80s Chrysler Spark Control Computer, and it's still working fine to this day).

I have been stockpiling "discontinued" parts for a number of years now. I have spare PCM's, TCM's, climate control panels, instrument clusters, and a spare AW-4.

I should have been stockpiling discontinued parts long ago, I have started now. I guess I am influenced by my experience last summer where I had to scrap an 18 year old Chrysler mini-van because the TCM in the wheel well was water damaged. I was searching for a year for the correct used part. Other deterioration over the year through lack of use and moving house forced the decision. I don't want to be in that same situation with either of my XJs.


I also scrapped a large number of 'vintage' computers for 1995-2001 (i386 to Pentium2). All of them were dry stored but so many had dried out capacitors. Some booted up a couple of times, but most of them died within a few hours. I saved 6 of 13 younger 64-bit Dell servers I had from 2008-2009 but I had to replace all of the capacitors on the SAS controllers. The seven that were scrapped all had PSUs that didn't last more than a few hours of bench testing. A year later, I'm not that confident that the six I saved will power up now. The point that I am trying to make is that electronics don't last forever. Is the expectation of XJ electronics to last 30 years or more, either on the Jeep or on a shelf too much?

Tim_MN said:

I have been stockpiling "discontinued" parts for a number of years now. I have spare PCM's, TCM's, climate control panels, instrument clusters, and a spare AW-4.

Click to expand...

I've started stocking up on various things as well. Not just parts no longer produced but items which could leave me stranded or without a vehicle, just general spare parts. I keep them on the shelf in my garage. Most parts stores don't seem to stock many of our parts on hand and have to have it shipped in from a warehouse either later that day or next day. Sometimes longer.

IMO, consumer grade computers were designed to be cheap to make and disposable, automotive electronics from the era Cherokees were built are robust and were built with parts designed to last despite the harsh conditions they live under.

My parts bin contains multiple examples of all the OBD engine sensors and other parts that would be difficult to locate and buy, or expensive to ship. I could probably buy a stripped XJ shell and get it on the road in a week or two.

OK, I have a plan for my '93 that is not subject to more modern emissions regulations. After reading lots of other forums on MegaSquirt, V8 Land Rovers and Mopar V8 site in Netherlands, I was really pleased to find that I can control both gasoline and propane on the same MegaSquirt which will save a lot of money.

Interestingly, the MegaSquirt can also control Nitrous Oxide. I still have some research to do about the VSS. I'm also going to move the CPS to the front of the crank like the Hesco kit. I did that conversion on my TJ. It worked really well and was easy to get at.

My 2001 is going to be a bit harder to resolve with stand alone electronics. Because it is younger, it is tied up by EU emissions regulations and has to have EOBD2 so I cannot simply ditch the factory PCM. I will have a chat with the relevant government department to ask what happens if I transplant an older engine into it that is not governed by those regs. My engine only needed to be three months older to avoid most of the legal crap. It was registered in March 2001 and was from the final export batch of XJs to the UK. I am hoping if I can get an earlier NVH engine from a WJ/WG to use as transplant. In reality, I only need the block, the block serial number and the paperwork adjustment. When the block actually gets used may not matter as the location of the number on the casting isn't recorded on the inspector's computer database. They usually don't know where to find the number so cannot check it at the emissions test. That's every 4.0L Jeep sold in the UK between 1993 and 2006 having only a VIN check.


Air-bags are going to be a problem. The warning light coming on and going off is on the annual safety test. I had to fix that last year with a new ignition switch gizmo. I reckon that one is going to be a chat with a lawyer. How do we deal with obsolete 20+ year old air bags not on the Tekata recall list?

Vince said:

Is the expectation of XJ electronics to last 30 years or more, either on the Jeep or on a shelf too much?

Click to expand...

I think one of the biggest challenges for many people is going to be the legislative side of the picture. The work-arounds that could keep an XJ running may not be acceptable at an emissions check. And then you have the great state of Kalifornia (whose example everyone else seems compelled to follow for some mindless reason) which is working on getting rid of all vehicles with internal combustion engines (Yes, I know, existing vehicles are "grandfathered". I have been through any number of iterations of the Smog program where they changed the rules to suit whatever whim pleased them at the moment. I have no faith that they will not rescind the "grandfathered" status). Cash for Clunkers was just an example of what the government is willing to do to get rid of vehicles that don't suit their latest feelings. I think that picture is much more likely threat to the continued operation of our vehicles.

That would be a good reason for us to be supportive of SEMA. They lobby for the rights of automotive enthusiasts.

Tim_MN said:

IMO, consumer grade computers were designed to be cheap to make and disposable, automotive electronics from the era Cherokees were built are robust and were built with parts designed to last despite the harsh conditions they live under.

Click to expand...

I agree 100% with the computer comparison. I mostly agree with what you say about automotive electronics reliability. However, my experience with Chrysler electronics made in the Daimler era doesn't give me that same level of confidence (two Voyagers, a Neon, WG, TJ and XJ). My '93 has been mostly fault free, except for this year with the wiper controller (still unresolved). My 2001 definitely doesn't have anywhere near the same level of reliability with its electronics and electricals.

Anak said:

I think one of the biggest challenges for many people is going to be the legislative side of the picture. The work-arounds that could keep an XJ running may not be acceptable at an emissions check.

Click to expand...

My 2001 is currently subject to a law that was back dated 10 years concerning catalytic converters. I had a replacement fitted that passed 5 years of smog tests that suddenly became illegal because it didn't have an OEM serial number. My current brand new catalytic converter is a magic one delivered by a friendly leprechaun driving a FedEx truck and will certainly pass emissions next year despite Fiat disposing of all of their EU stock in 2010.


I looked at the latest regulations today, and my 2001 XJ will be exempt of all EOBD2 regulations if the 4.0L is replaced with an electric motor.

I had the same sort of ridiculous nonsense happen with my catalytic converter in Kali. What was legal one year suddenly wasn't 2 years later because it didn't have the newly required OBDII/CARB EO stamp on it. Tailpipe emissions didn't matter. What mattered was that the right palms got liberally greased.

Fighting natural deterioration is one thing. Fighting the bullies who pretend to be public servants is another matter entirely.

Anak said:

I had the same sort of ridiculous nonsense happen with my catalytic converter in Kali. What was legal one year suddenly wasn't 2 years later because it didn't have the newly required OBDII/CARB EO stamp on it. Tailpipe emissions didn't matter. What mattered was that the right palms got liberally greased.

Fighting natural deterioration is one thing. Fighting the bullies who pretend to be public servants is another matter entirely.

Click to expand...

You need a shelf cat, one that stays on the shelf till needed.

That is exactly what I did.

My local law says the inspector is not permitted to remove any components during the test. Some modern cars have OEM underbody panelling that restricts access to some engine parts. It is not unusual to be unable to check OEM markings on test components. The testers just mark it down as not accessible. Additional heat shields and skid plates have been a worthwhile investment. Mud baked onto a catalytic converter is similarly protected by law.

Black1990jeep said:

You need a shelf cat .....

Click to expand...

Would I need a litter box also ?

No.

That is the whole state.