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RENIX computer gets HOT!!!!

W

wf_s10

NAXJA Forum User
Location
eufaula alabama
1990 4.0 computer gets hot after running for about 20 mins so hot that if you hold your hand on it for more then 10 secs or so then it will blister you It has power(drive ability) when cold and power reduces when hot motor temp is 200 when at temp the computer is BENDIX 53007842 im sure im leaving needed info out so if you need more info just tell me
 
The ECU grounds at the engine dipstick tube stud. Remove, clean off paint and oil, polish terminals and reinstall securely. Poor ground equals heat. Good place to start and the poor grounding at the stud is a known issue.
 
Note from DJ
Info on grounds from cruiser54:
Grounds can be the root cause of many electrical gremlins. Refreshing grounds is NEVER a bad idea!

You can't just check or look at these grounds. You must remove, scrape & clean until shiny all the cable/wire ends and whatever they bolt to. Pay special attention to the one on the back corner of the head, and where it attaches to the firewall. Scrape the paint from the firewall. Best to replace that woven cable with #4 or #2 gauge cable. You can attach the one end to the intake manifold if you would like.

Next go over to the engine dipstick tube stud. There are 3 grounds at the engine dipstick tube stud. They are the ground for very important sensors. Remove the nut, clean the ring lugs and check to see if the small wire ring lugs are soldered or just crimped, if they are crimped only, replace ring connectors then clean & solder them. Before bolting everything back on, make sure the stud is clean and shiny with no grease and no paint plus scrapes the block until shiny at the stud. Then you can reattach every thing and tighten it up tightly.

Note from 5-90 “Battery to Engine Block next to oil dipstick support is a stud with a nut, but can be replaced with 3/8"-16 x 3/4 or 1" Hex Head Bolt. Since that's an electrical connection, I'd suggest using brass or bronze bolt to replace it with. Then use brass flat washers to take up the slack if needed”.

If you are so inclined, add at least a #6 cable from the negative terminal of your battery to one of the bolts on your radiator support. Scrape the paint off first.

Clean both battery cables, and verify that you have at least 12 volts with a voltmeter at the battery. Borderline low voltage could also cause your problems.

Refresh all your grounds and add some. Good advice above from Curtis_H. I wouldn't spend another minute or another dime on your problem till the "ground work" is done. Pun intended.

The grounds are super important but most people just blow off that suggestion as being some kind of BS for some reason. Truth is, those of us who lived with these rigs when new at the dealership have seen the benefits of the factory recommended ground refreshing.

Without reading your post, I must ask if you have done all of your ground refreshing suggested above plus, C101 cleaning and connection tightening, engine sensor connector cleaning and tightening, and ECU connector cleaning and tightening, these items are often overlooked.

Sad part is it costs nothing out of pocket and very little time to perform these procedures. People just resist believing something so simple could solve their complicated running problems.
-----------------------------------
Posted # 19 by Curtis_H: http://www.naxja.org/forum/showthread.php?t=1053601&page=2
I had this in the Waggy for a long time. I changed every damn sensor on the engine literally. Also put in new ford injectors. When that didn’t work I started looking at the wiring. Check the input voltage on the map sensor and the TPS, both should be at or very near 5v. Check the resistance to the negative post on the battery from both sensor grounds. There should be very little to none. I ended up cleaning all my grounds, adding a 4/0 ground from battery to body, cleaning every connector on every sensor, replacing a few bad ones, fixing a couple of corroded wires here and there and now it is running much better. I still can't say it is perfect, but it is much better. Renix are extremely finicky when it comes to grounds so check every one you can find and then find the ones you cant see and check those and then add a couple and check those too and then re check them all and add 37 more and you should be good to go!!
Or Joe Peters quote “You have got to have good grounds. Without good grounds your coffee will taste like crap and your electrical components will behave erratically”.
-------------------------------
OP- steering column ground http://www.naxja.org/forum/showthread.php?t=1051303
There is a common ground for the blinkers and other items that causes weird problems when it gets flakey. It is located in the driver's side rear, under where the spare is located. You have to remove the plastic.
 
Thanks for the help will get out there in morning and clean all of them does my 1990 have the c 101 plug and if so where would it be located
 
The computer should not be running hot. Mine was running very hot then crapped out. I replaced it and the new one is running at ambient temps.
 
cruiser54 said:
The ECU grounds at the engine dipstick tube stud. Remove, clean off paint and oil, polish terminals and reinstall securely. Poor ground equals heat. Good place to start and the poor grounding at the stud is a known issue.
Click to expand...

What do the grounds have to do with an overheating ECU?
 
OK my grounds are good added a few more but if you are rideing down the road it gets so hot it is like having the heat on high and rite on on my legs i have to turn the ac on to bi-level to cool my legs off my first thought was that it was the heat blowing out by the plentem box the door is shut good checked and i have no water in the heat core do to the shut off but outher then the high heat it runs good just after it gets how its low on power
 
Note from DJ to Ecomike
Regarding your question “What do the grounds have to do with an overheating ECU?”
I was hoping that that wf_s10 had a very poor ground connection in his main system some place and that the system was back grounding through the ECU causing it to overheat.
But according to his post # 12 on 9-3 bad grounding problem was taken care of and problem is still there.
Well at least some of his possible pore ground gremlins have been eliminated.
 
Ecomike said:
What do the grounds have to do with an overheating ECU?
Click to expand...
X2

Overheating is caused by a faulty component, either internal to the ECU or external. A bad sensor that is powered by the 5v from the ECU that is pulling too much current it a likely suspect. Other than that, an injector that is too low an impedance is the second most likely. Third would be an actual injector driver in the ECU may be faulty or on its way out.
 
does any one have a diagram of what voltage should be coming from what so i can test and see what i'm getting where and on the injectors how would i test the impedance and what would be a good impedance
 
Ok ill get out there and check them after the rain stops but one thing i forgot to to mention was that if i stomp the gas to the floor off ideal and let off real quick the motor almost dies
 
Note from DJ
I am sorry OP wf_s10 that all of your checking has come up with no negative results, I was hoping that something positive would turn up.

ECU failures in XJ are very rare but it looks to me that you have one; I have worked my computer a lot searching with many different combinations of words to no avail at finding some other cause for your Hot
ECU.

The only advice that I can offer you is start searching the junk yards for a replacement ECU. I am afraid that if you don’t try a replacement ECU something bad is going to happen, like the Jeep will suddenly stop and never start or some wiring is going to melt and possible cause a fire. Or if you are good at electronics you can remove the cover on your ECU and look for a hot looking spot unsolder the bad looking components and replace them. This procedure has been posted on this site in at least one occasion with success.

If you decide to go junk yard searching hear is some information that may help in your search.
Any ECU from a 1987 through 1990 is supposable compatible for your Jeep, the best one is from the 1990 model year it has the latest programing which is the same numbers you reported that you have which was the 5300 5428 this number was for the 6 Cyl. Engine, w/Auto. Trans. So that is the one you are searching for, it is slightly possible you could find that same number in an earlier Jeep, the last four digest are the most important.

If you go to a pick and pull type of junk yard this info may help in your search. Look for the VIN. Number of any Jeep that looks possible a good donor. What you are looking for is the 10 digit example being my Vin. # starts like this 1JCMT7848J the letter J is the key to the Model year, H=87, J=88, K=89 and L=90you are looking for another L mine is a J and it is a 1988.

Hope this info is of some help to you, this is the best information that I can offer, at this time.

Please post back what you do to resolve the problem or not, But I will look for a successful fix.
Here’s hoping!
 
im not to bad with electronics so i may just open the case up and see but today i got a ground problem my cp player got this whine and the light on my oil psi gauge did not work so what grounds are under the dash that have to do with this and the ecm didnt get hot with the radio whineing
 
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