Error 4121 and crazy stuff

Thanks much Mike, I appreciate the info. Is the fuse also missing on your car?

Randall

 

I learned this morning that my assumption that it was the 1-4 cyclinder bank not firing, it is in fact the 5-8 not firing. I have switched sides for everything in the trunk and nothing fires it up. I have spark and I have checked all wiring, igniters, relays, etc. I guess that I now have to address the fuel pump directly to see if it is powering up. The fuel pump relays and the fuses for the pump and the injectors have been switched with no result. I have replaced a couple of relays after having checked them on the 1-4 side.

Any suggestions or pointers on how to check the fuel pump on the 5-8 side. Should i tap on it like on my BMW? or just check wiring and voltage? How about access? Any pointers outside of the WSM? Is the replacement difficult?


Thanks for your help.

 

As a last resort today before getting into gynecology mode, I checked the TPS's by measuring the resistance across some of the terminals. The resistance did change on two of the terminals as the potentiometer changed position so I am assuming that they are ok since they were both giving the same data. Now, I have my speculum in hand and will try to find the culprit.

I will first try to find the power to the fuel pump for the 5-8 bank but only after checking the grounds.

Any suggestions/comments will be more than welcome.

 

After some useful consultation from the original stooge, Ernie, I switched the motronics ECU and what do you know, the problem switched sides! So now will exchange the EPROMS with updated software thanks to wonderful people here on fchat. This place is unique. To be continued.

 

Here is a photo of one of my EPROMS. Number on the EPROM is different that that of the EPROM shown in Ernie's stooge replacement thread for his 348. Mine are 410 and his are 497. Any real differences?
Image Unavailable, Please Login

 

Changed EPROMS thanks much to 3forty8 and the guidance from Ernie and Eric and their threads. Eliminated battery shutoff switch. No change. The four cylinders that are running sound smoother. I do now have a check engine light for 5-8 bank that was not there before. But no firing on the 5-8; change ECU's and the problem switches sides. Am I in for new ECU or its repair? Any suggestions would be appreciated.

 

Done.

 

Tomorrow morning.

R

 

The only codes was 4121 which is an error code overheated catalyst. Of course the catalyzer that side is cold because nothing is firing and I have unplugged the thermocouple and no change. I really think the ECU needs psychiatric help. Guess we have a continuous signal indicating an overheated catalytic converter and regardless of taking the thermocouple away it still blocks the 5-8 bank? However I am getting the same error from the 1-4 bank. I guess that the fact that 5-8 is not firing that the ECU's are not relearning after replacement of the EPROMS? Anyway everything is only warm and there can be no overheated catalyzers.

 

I have just redone all of the major grounds and bypassed my battery cutoff switch. I have NOT however looked at those grounds you mention. Thanks.

 

I switched the ECU's again and it does NOT switch sides so I assume the ECU's are fine. I am getting spark on the dead side so I guess I need to return to my fuel pump. I am using an inductive coil pick-up timing light to determine that I am getting spark. Is there a problem with this? Can I be fooled into thinking I have spark when I don't using this method? Any suggestions would be deeply appreciated.

 

I remember that episode very well. I cannot check that right now but it is next when I eliminate a bunch of other stuff first. Thanks

 

In the trunk on the Mondial. Remove the carpet panel on the firewall. and they are there on each side. Look at the pics earlier in this thread it shows them.