8v92/DDEC II Problem

This one has me stumped and has put me to the side of the road a couple of times. I have an 1989 XL with an 8v92, DDEC II. Once in a while, the SEL, CEL, and Cruise control lights come on while driving down the road. The bus loses power, but the lights go out if you lift out of the throttle, and the power resumes like nothing happened. No smoke when this happens. This used to happen occasionally, and only when the cruise was on. Now it happens with cruise or normal driving. Mostly on the highway, and seems to be happening more often. It also seems to happen after 4-5 hours of driving in hot weather (mid 90's). The other day, it kept happening when I lifted out of the throttle and it would only run at about 15 mph. Pulled over, wiggled the wires after a restart (no change), and it ran fine for another hour until the next stop.

It does not throw a code. I have done the wiggle test and got nothing, voltages at the ECM are good. No bent pins, and I used some contact cleaner on the ECM plugs/terminals with no change. I've tightened all connections on the front and back junction panels, replaced all the relays in the ignition and engine run circuits, and replaced the rear start switch. Figured I couldn't go wrong with those, seeing as it is 21 years old. Engine runs great otherwise. Any one ever have this happen to them and know of the fix?

Jon - I know you don't like chasing intermittent problems, but I have a feeling that this one is going to leave me by the side of the road and require a tow..... I'd like to prevent it if possible.
Thanks
Steve

I would look at the coolant level and or sensor. The level tends to drop while under power on those and can set the Cel but not register a code. How are you retrieving the codes?

Steve,

Does your coach provide you with the ability to flash the codes? If you don't have a reader, but can flash the codes (my 87 chassis was DDECI and I had to jumper between two pins in the steer compartment) you might get a code that will help lead you to the problem. I think the time to try to pull codes is when the SEL and CEL are on.

But you are right. The intermittent stuff is very difficult to diagnose without clues.

I have no logical basis for saying this, but is there a chance the throttle position sensor has a part in this? I had a turbo boost sensor go bad once and it impacted my ability to give the engine throttle, but it never lit up any lights.

I have a Pro-Link to read the codes. This issue does not set a code and I don't have any historical codes either. The lights don't stay on long enough to get the Pro-Link on it. They will go out if you back out of the throttle and then get back on - which is what you need to do to get to the side of the road. Good idea though, I'm going to take the Pro-link out and have it ready and maybe I'll be able to have it happen when it is safe to get to the side of the road without touching the gas pedal.....

I have plenty of coolant, and am pretty sure the level sensor is working properly - I replaced the exhaust manifold gaskets two weekends ago and the CEL/SEL was on when the coolant was drained, and off when it was refilled. I could jump it next time it starts happening and see if that helps.

As for the TPS, I was thinking that it may have something to do with the problem. However, when the problem originally started the symptoms would only happen when the cruise control was engaged. Now that I think about it, I'm not sure I ever let it go to see what would happen if I didn't step on the gas. Once again, at 21 years old, replacing it and keeping the old one as a spare might not be a bad idea.

The three lights come on just like they do when you turn on the ignition, and stay on for about that length of time. That's why I have been chasing the possibilities in the ignition/engine run circuits.

Keep the ideas coming!!

Quote:

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Originally Posted by stevet903

I have a Pro-Link to read the codes. This issue does not set a code and I don't have any historical codes either. The lights don't stay on long enough to get the Pro-Link on it. They will go out if you back out of the throttle and then get back on - which is what you need to do to get to the side of the road. Good idea though, I'm going to take the Pro-link out and have it ready and maybe I'll be able to have it happen when it is safe to get to the side of the road without touching the gas pedal.....

I have plenty of coolant, and am pretty sure the level sensor is working properly - I replaced the exhaust manifold gaskets two weekends ago and the CEL/SEL was on when the coolant was drained, and off when it was refilled. I could jump it next time it starts happening and see if that helps.

As for the TPS, I was thinking that it may have something to do with the problem. However, when the problem originally started the symptoms would only happen when the cruise control was engaged. Now that I think about it, I'm not sure I ever let it go to see what would happen if I didn't step on the gas. Once again, at 21 years old, replacing it and keeping the old one as a spare might not be a bad idea.

The three lights come on just like they do when you turn on the ignition, and stay on for about that length of time. That's why I have been chasing the possibilities in the ignition/engine run circuits.

Keep the ideas coming!!

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TPS will almost always set a code. Check the "priority" of the "low coolant" sensor code with the Pro Link. See if it is set to "shut down" when detected. Be real careful as that series is prone to ECM failure. You might go to start it and it will just crank over with out starting.

[QUOTE=stevet903;65140]This one has me stumped and has put me to the side of the road a couple of times. I have an 1989 XL with an 8v92, DDEC II. Once in a while, the SEL, CEL, and Cruise control lights come on while driving down the road. The bus loses power, but the lights go out if you lift out of the throttle, and the power resumes like nothing happened. No smoke when this happens. This used to happen occasionally, and only when the cruise was on. Now it happens with cruise or normal driving. Mostly on the highway, and seems to be happening more often. It also seems to happen after 4-5 hours of driving in hot weather (mid 90's). The other day, it kept happening when I lifted out of the throttle and it would only run at about 15 mph. Pulled over, wiggled the wires after a restart (no change), and it ran fine for another hour until the next stop.

It does not throw a code. I have done the wiggle test and got nothing, voltages at the ECM are good. No bent pins, and I used some contact cleaner on the ECM plugs/terminals with no change. I've tightened all connections on the front and back junction panels, replaced all the relays in the ignition and engine run circuits, and replaced the rear start switch. Figured I couldn't go wrong with those, seeing as it is 21 years old. Engine runs great otherwise. Any one ever have this happen to them and know of the fix?


Steve


Did you fix or figure the problem out? We have an 89 XL Marathon 8v92 DDEC ll 90,000 miles. We're in Twin Falls and are having similar issue;


Start engine and let run about one minute then hit high idle switch
Engine will run for seconds to minutes then the three lights (SEL, CEL, & Cruise) will come on
Engine will drop to low idle
This has happened a couple times while driving after an hour or two and unfortunately I didn't think of working the throttle pedal as I was checking gauges and mirrors while trying to get to the shoulder
Most of the time engine will continue to run at low idle and the three lights will go out
A few times the engine shuts off
I can start it back up with no trouble and it will go to high idle again when switch is pushed
Engine will run for seconds to minutes then the lights come on and down to low idle again, lights go out and engine continues to run at low idle
It has "cured itself" or at least not happened for weeks until now and I am concerned about its intermittence and don't like worrying about it while traveling
Ive done everything in your second paragraph except replace the rear remote start switch and check voltage at ECM
I have a 16 and 43 code (I got codes by jumping A and M with paper clip as per Prevost)
I replaced the coolant sensor and coolant module
Batteries are good (5 months old) 12v+ eng off with batts disconnected from each other, 13v + eng running
Checked 12v switch with engine running and voltage is 13v+

Someone told me to check ECM in-line fuses, but I don't see any???

Ive been working on this for a week plus and not any closer to a fix and we need to head to Bozeman next Monday, I'm taking it to a DD repair shop (Jerome Freightliner, unless someone has a better? shop) as soon as they can get me in unless you had an Aha moment that resulted in a fix.

Thanks

I would call Prevost ; 800 463 7738. It may be as simple as a reset. I recall a sequence of turning the ignition key on and off 2 or 3 times and then starting but I could be thinking of something else.

I called Prevost and talked with two people, they "have never heard of such a problem".
Surprising to me since I've found at least 10 people with the same issue.

Update...

Our problem is solved or so it appears.

I have learned always check the ECM power connection / connector for corrosion before checking anything else.
If I would have done that I would have saved myself time, money, and endless of searching the internet
for a cure.

Happy motoring

Replace the throttle sensor, or it will or may happen again.