Dodge SRT Viper Forums : ViperAlley banner
21 - 40 of 42 Posts

·
Landscaping Professional
Joined
·
14,090 Posts
I believe crank tooth count is 0.5:1 cam. Here is the stock JTEC functional overview:

Font Material property Screenshot Document Publication
Human body Font Rectangle Parallel Slope
Rectangle Font Parallel Slope Number

Automotive tire Motor vehicle Auto part Engineering Automotive wheel system
 
  • Helpful
Reactions: RobV and 8.0L>1.8T

·
Registered
Joined
·
705 Posts
Discussion Starter · #22 ·
I did check the ASD relay, swapped it with one of the other, less often used relays. Even took the PDC apart to fix some of the contacts that weren't grabbing onto the relay pins very well. Checked all the fuses.

The cam sensor signal was almost a perfect square wave, 0 & 4V. The crank sensor signal has pairs of pulses, caused by the 54 then 90 degree separation of the cylinder firings. I didn't take a long enough sample to see a whole 720 degrees, but it's really likely that it's working right. I'll get a full 720 degree sample anyway...
 

·
Landscaping Professional
Joined
·
14,090 Posts
The cam sensor signal was almost a perfect square wave, 0 & 4V. The crank sensor signal has pairs of pulses, caused by the 54 then 90 degree separation of the cylinder firings. I didn't take a long enough sample to see a whole 720 degrees, but it's really likely that it's working right. I'll get a full 720 degree sample anyway...
It could be that the CKP signal could go to 5V if it was slightly closer to the high spot on the cam. The spacer that came with a new ones were just about the same thickness as a manila file folder. But as hard as they are to come by, it isn't worth the risk.
 

·
Premium Member
Joined
·
2,661 Posts
I would check the relay terminals for voltage and continuity then jumper the terminals without the relay (hard wire).
both the cam and crank will be square waves and what Dean showed in the third picture is what you will get for 1 round of the crank. What you stated sounds like the senors are working correctly.

So my eyeballing of the cam gears was correct. Cam:crank = 1:2 or 0.5:1 and the crank pulse widths are equal. thanks to Dean for confirming and providing the crank cross section.

Are you back probing at the ECU pins or at the senors? If at the ECU, looks like your AEM ignition circuit is toast but you can probe the ignition output pin to confirm. I would do it 2 ways, back probe the pin and if you get no signal, remove the wire to eliminate shorts from the pin and probe the pin. remember that the stock PCM controllers the ground side of the ignition coils NOT the hot side.

If you have the firmware I would reload it maybe you will be luck and it got corrupted some how.
 

·
Registered
Joined
·
705 Posts
Discussion Starter · #25 ·
I've checked the voltages at the relays and jumpered the relays too. No change.

I've looked at the AEM coil outputs at the inputs to the ignitors, which is the AEM output pin + a wire. None of them show any activity. A five point failure is unlikely, so what probably happened is something common to the 5 coil outputs failed and so none of the cylinders are getting any spark. The coil output signals from the AEM all come from the same IC driver, so it's possible that one of them going wonky broke the whole IC. Something did pull a lot of current when this happened, because the 20A ASD fuse blew.

I've reflashed the firmware twice, once updating it from v96.2 to the latest, v96.5, then went back to v96.2. Apparently the tuning data format is different in the updated v96.5 version. While it can be made to convert it automatically, I wanted to go back to the original version and use an unedited tune file. No spark in either version.

I'm going to look at the inputs to the coil driver IC in the AEM next, if there's signals there, and I know there's no signals coming out of it, I'll replace it and it will (should, might, maybe, probably won't) run again.
 

·
Premium Member
Joined
·
2,661 Posts
The information I post in my posts are for anyone reading threads that might not know the technically stuff and I try to word them for all readers not just tspargo who's electrically knowledge is a pretty high.

...I've looked at the AEM coil outputs at the inputs to the ignitors, which is the AEM output pin + a wire. None of them show any activity....
Activity as in constant 0V?

You should see 12V on all the pins. It is NOT coming from the AEM but from the ASD. The AEM is pulling the trigger pins low (to ground). The primary side of the coils always have 12V going to them from the ASD. Check pin 3 on the left coil pack and pin 2 on the right pack for the input 12V. then check the trigger pins going to the AEM for the 12V coming from the output side of the primary coils. This is when the relay is activated. the ASD relay only activates in the key ON position (this for stock PCM) for 1sec then deactivates if the PCM does not see a crank sensor followed by a cam signal (i.e. key in START/CRANK position or engine running). But from your other post about fuel pressure, the fuel pumps are running during cranking, so my guess is the ASD is working but I would check the circuit since it blew the fuse.

Remember the coils are not directly controlled by the IC but through electrical switches (power transistors, mostly likely MOSFETs), so if you are not getting any spark the driver controlling the MOSFETs is shoot unless all the MOSFETs blew. But I don't think the AEM is bad since you mentioned the 20A ASD fuse blew.
 

·
Registered
Joined
·
705 Posts
Discussion Starter · #27 · (Edited)
A couple posts up I did mention that I'm seeing the battery voltage on those pins. I know it doesn't come from the AEM, I have the service manual. And it's not 12V- this is when the starter is running so the voltage drops down to 9 or 10V.

I've checked all the fuses. The ASD is the only one that blew and it's been replaced. I also checked the ASD relay. It's working.

The coils are driven by the ignitors which are driven by the IC in the AEM, it's just a basic 5V driver. This is different than how the stock PCM works, as you noted :)
 

·
Premium Member
Joined
·
20,153 Posts
Do you want me to send you another AEM computer to try? These things were notorious for having bad grounds and failing
 
  • Helpful
Reactions: RobV

·
Registered
Joined
·
705 Posts
Discussion Starter · #32 ·
I fixed it. The problem was in the Infinity. I opened it up and looked at the waveforms going into the coil driver IC's ( 74AC541 line drivers) . The amplitudes looked too small, 2.76V with 5V logic, which could mean that whatever is driving the coil drivers was bad; despite that, I decided to replace the coil driver since there are two of them (each one drives 5 coils, so one of them wasn't being used), and to my shock and amazement, it starts now.

Thanks for all the advice and offers for help. Now to figure out the fuel pressure problem, if it still is happening.
 

·
Landscaping Professional
Joined
·
14,090 Posts
That's great news! So there are 2 coil drivers? 1 can fire 5 dual pole coils, or the two can fire 10 individual coils - so you are just using the second one alone now?
 

·
Premium Member
Joined
·
2,661 Posts
That's great news! So there are 2 coil drivers? 1 can fire 5 dual pole coils, or the two can fire 10 individual coils - so you are just using the second one alone now?
I looked up the datasheet. That IC is not the driver/switch to the coils.

Plus that 2.7V could be correct to drive the mosfet. But i don't have the board nor schematic.
 

·
Registered
Joined
·
705 Posts
Discussion Starter · #35 ·
Sorry, I should have been calling them ignitor drivers. The ignitors drive the coils and the IC I replaced drives the ignitors. The Infinity uses ignitors between itself and the coils. No MOSFETs in the Infinity for the sparks, there might some in the ignitors though.

Yes, it can drive up to 10 coils from 2 IC's, 5 each. So I removed both of them and soldered the good one where the bad one used to be.
 

·
Registered
Joined
·
705 Posts
Discussion Starter · #36 ·
The 2.76V is barely enough to be recognized as an input 'high', so that's why I though the prior part in the path was the problem- it should be up at 4V or even 5V amplitude. However the bad ignitor driver may have been affecting the input voltage amplitude, making it lower than it normally is.

I don't have a schematic either. I did ask AEM and Engine Labs for one but not surprisingly, they couldn't let that out- proprietary, confidential, etc. It was a long shot.

At any rate, it works now. I'm going to order a new ignitor driver IC and put it in. Taking the good one out involved a LOT of heat and some bending of the leads, I wouldn't trust it to be very reliable.
 

·
Premium Member
Joined
·
2,661 Posts
No way you are getting the schematic from any company. You and others are stuck reverse engineering the board.

The 74AC541 is octal buffer/line driver (8 inputs/ouputs).

The what is the ID number on the ignitors if they are covered by the heatsink you can see them?
 

·
Registered
Joined
·
705 Posts
Discussion Starter · #38 ·
ID #? You mean the P/N? There are two, 4 channel ignitors. One uses three of the four, the other uses two out of four. A case of up-selling the customer- they could have used two of the 3 channel versions. Grrr.

If you mean something else, I have them on a heatsink and a mounting plate with thermal grease, bolted together and Loc-Tite'd. I can see the P/N but that's all. If you really want to know what's on the back, I'll unmount it...
 

·
Registered
Joined
·
705 Posts
Discussion Starter · #39 ·
In the unlikely event that someone else needs to replace one of these, make sure to get the correct package type- SOIC (small outline IC). I had actually ordered and received them, only to find I'd goofed and ordered the wrong package. Currently these parts in the correct package are on backorder, none available until early 2023.
 
21 - 40 of 42 Posts
Top