rdx4me
NAXJA Forum User
- Location
- NW Florida
Has anyone replaced the RENIX ignition system with a better one? I hate getting in my 90 XJ and cranking away... There has to be a better solution.
RDX4ME:hang:
RDX4ME:hang:
-
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RENIX Ignition
- Thread starter rdx4me
- Start date
5-90
NAXJA Forum User
- Location
- Hammerspace
There is a known quirk of the RENIX system that you are running into - the ECM does NOT send any ignition or fuel injection pulses until it reads 300rpm at the CPS (on the rear of the engine.) This is done to promote oil circulation on startup - by the time the engine is ready to "catch," it is being oiled. I honestly think this isn't a bad idea...
Changing the module and going with something like an MSD won't make a difference - it's an ECM thing.
If you want to do something about it, I can suggest two things to stay on top of:
1) Make sure you always have a strong battery to start. This will allow the starter to get the engine up to speed that much quicker.
2) Look into getting a new starter - especially since yours is now 15 years old. If you can, find a local shop to rebuild it for you, and tell them you want a "high-torque" starter so your engine can get up to "starting" speed that much quicker. If he asks, explain why - not a lot of shops seem to know about this (it's a known quirk among enthusiasts...) and you just might help your local shopowner out - which can help you later. I have a rebuilder I've been dealing with for years - I got my last starter (which was actually for me!) for $40 - it was a high-torque unit for my 88. I got a 140A alternator from him for $60. Yes, they both work well and still give max output. This man makes parts that I can install and forget about.
5-90
Changing the module and going with something like an MSD won't make a difference - it's an ECM thing.
If you want to do something about it, I can suggest two things to stay on top of:
1) Make sure you always have a strong battery to start. This will allow the starter to get the engine up to speed that much quicker.
2) Look into getting a new starter - especially since yours is now 15 years old. If you can, find a local shop to rebuild it for you, and tell them you want a "high-torque" starter so your engine can get up to "starting" speed that much quicker. If he asks, explain why - not a lot of shops seem to know about this (it's a known quirk among enthusiasts...) and you just might help your local shopowner out - which can help you later. I have a rebuilder I've been dealing with for years - I got my last starter (which was actually for me!) for $40 - it was a high-torque unit for my 88. I got a 140A alternator from him for $60. Yes, they both work well and still give max output. This man makes parts that I can install and forget about.
5-90
Matthew Currie
NAXJA Member #760
- Location
- Vermont, land of big clay
5-90 said:
Just curious about the 300 rpm thing. I always thought it just counted to 4 revolutions. My 87 always did 4 regardless of the considerable seasonal variations in cranking speed. I don't suppose it matters, since the outcome is about the same, but I was wondering what your source was.
I'd also alwayas assumed the oil issue was a by-product, and the reason it did this was because the computer sets timing on the fly. I figure it would have to get a sample of several timing impulses before it could safely establish a timing base.
Last edited:
Ron Hyslop
NAXJA Forum User
- Location
- Madison, WI
I've been told by a long time jeep tech that the RENIX won't send an ignition pulse until it gets a valid signal from all sensors and two from the CPS.
Ron Hyslop
NAXJA Forum User
- Location
- Madison, WI
Also, check your fuel pressure, when my fuel pump check valve was dying, crank times were a lot longer
5-90
NAXJA Forum User
- Location
- Hammerspace
I don't recall precisely where I saw the oiling issue - but it's stuck with me and has made a good deal of sense (yet it may be apocryphal - gotta check the Archives on that...)
Meanwhile, back at the ranch...
From Jeep 4.0 Liter Multi-Point Fuel Injection (1987-1990 RENIX system)
page 77
"CRANK MODE
OPEN LOOP
...
The eengine crank input from the starter relay provides a signal to the ECU to energize the fuel pump relay and to begin the start sequence. The ECU determines the correct cranking speed (approximately 300 rpm) by counting the flywheel teeth passing the speed sensor. With the proper cranking input the ECU will synchronize the fuel injector opening and the spark plug firing.
...
NOTE: If the ECU detects a wide open throttle condition, the ECU assumes that a flooding condition exists. It will open all circuits to the injectors (meaning they will all be off - Ed.) and will not resume fuel injector opening until enging speed reaches approximately 400 rpm."
This is, in fact, one of the points I plan on testing when I finally get my RENIX simulator set up. I've got the parts out in the shop - I've just got to figure out how to mount them, power them, and provide signals and simulate engine running speeds...
5-90
Meanwhile, back at the ranch...
From Jeep 4.0 Liter Multi-Point Fuel Injection (1987-1990 RENIX system)
page 77
"CRANK MODE
OPEN LOOP
...
The eengine crank input from the starter relay provides a signal to the ECU to energize the fuel pump relay and to begin the start sequence. The ECU determines the correct cranking speed (approximately 300 rpm) by counting the flywheel teeth passing the speed sensor. With the proper cranking input the ECU will synchronize the fuel injector opening and the spark plug firing.
...
NOTE: If the ECU detects a wide open throttle condition, the ECU assumes that a flooding condition exists. It will open all circuits to the injectors (meaning they will all be off - Ed.) and will not resume fuel injector opening until enging speed reaches approximately 400 rpm."
This is, in fact, one of the points I plan on testing when I finally get my RENIX simulator set up. I've got the parts out in the shop - I've just got to figure out how to mount them, power them, and provide signals and simulate engine running speeds...
5-90
Runnin'OnEmpty
NAXJA Forum User
- Location
- Southeast USA
It's hard to argue with the manual, but here goes:
I've read that the ECU needs a second signal from the cam position sensor (in the distributor), to determine if the #1 cyl is on the compression stroke. This is verified by comparing the CPS and CMP signals. Since the distributor only turns once for every two engine revolutions, the engine has to turn over (about) 4 revolutions for the ECU to get a valid second CMP signal. (In other words the ECU uses the CPS for ignition and injector timing, but uses the CMP signal to start the engine on the correct stroke.) If the 300 rpm theory is indeed correct, maybe it was used on the earlier Renix ECU's, and those French engineers in their infinite wisdom changed the ECU in later model Renixs'?
If I crank my 89 engine a couple revolutions, and let off the key without turning it to 'off', and then re-crank, the engine starts immediately. This tells me the ECU is counting the CMP signals, at least on my 89 model......
Ron Hyslop
NAXJA Forum User
- Location
- Madison, WI
My understanding is the cam pos sensor in the distributor sequences the injectors. After the engine is started it's signal is not required. My jeep dealer tech friend tells me the engine will run fine without the cam pos sensor. If he is correct, there must be another source of information about fuel injection sequencing for the ecu.
Digger87xj
NAXJA Forum User
- Location
- Buffalo Creek/Lakewood CO
Taken from Open loop crank mode, page 77 of the 87-90 renix FI manual:Ron Hyslop said:
"the sync signal input from the distributor provides the signal needed by the ECU to locate # 1 or # 6 piston. When the # 1 or # 6 piston is on its exhaust stroke, the ECU energizes the injector for that piston. The ECU uses either piston one or six as the number one in the firing order.
If the ECU does not recieve a sync signal input, it will randomly select an injector as number one in the firing order and use it to sequence the fuel injectors. the engine will probably start but performance will be noticeably poor."
