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Old 11-16-2013, 02:51 PM   #1
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Engine "miss" at 25-30 mph

When driving in traffic, pulling away from stop, accelerating on freeway onramp, etc. at about 25-30 mph, the engine misses, sort of like a loping thing, then it runs fine once it gets over 30. It also idles just fine. We took it to the Chev/Workhorse dealer and he put the scanner on it. Found codes P0404 (Exhaust Gas Recirculation Circ Range/Perf), P1514 (Air Flow to TP Sensor Correlation Hi) and P1635 (5 Volt Ref Lo). Unfortunately, he can't figure out the underlying issue and is suggesting a new throttle body, followed by a PCM if that doesn't solve it. He can't say specifically what is wrong and if the $800 throttle body (plus labor) doesn't fix it, it can't be returned. NO! Not a good solution, at least not at this point.


More about symptom: Engine actually only stalled one time. I was driving, thought it was on cruise but had hit the brake and took it off. I was actually coasting along on the freeway and the RPMs just kept going down. When I hit the gas to speed back up, MH had stalled. I pulled over and was able to start the engine right back up. This time the Service Engine Soon light came on steady. This is the only time this light came on and when we got home and turned the engine off, it did not come back on when engine was restarted.


Has anyone experienced this? Know what might be wrong? Do you have a good mechanic in the Orange County CA area who has experience with Chev/Workhorse vehicle? Looking for some input here, anything. Husband is retired auto tech. He understands the codes, but has no experience with this engine and no connections to anyone who has this experience.

2003 Airstream Land Yacht on 8.1 Chev Workhorse chassis
Mileage on this MH is about 36,000
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Old 11-16-2013, 03:08 PM   #2
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I would go after the EGR valve that will do the same thing you are saying it will even throw off the air flow. now I'm guessing that you have a 454 engine. but from the sounds of it that is what I'd say. not sure why the guy wants to replace your throttle body unless it has a lot of play in it. hope this helps also rescan it if all are still there clear codes drive it a little and scan it again to ensure the right codes are showing up.
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Old 11-16-2013, 08:13 PM   #3
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I know with only 36,000 miles it is unlikely but i would have the exhaust system checked for a restriction. A air flow code and a egr code are good indications that the system could be plugged. Logic would suggest if your not getting the airflow across the mass airflow and the egr is backing up do to backpressure the engine isnt breathing the way it needs to. A Good exhaust shop can either run a back pressure test on it or cut the converter off and look inside to see if restricted. Just my .02 good luck
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Old 11-16-2013, 08:37 PM   #4
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The P1635 can cause the other codes to set even when there is really no problem with TPS and EGR:


The PCM uses the 5 Volt Reference A circuit as a sensor feed to the following sensors:
  • The TP sensor.
  • The MAP sensor.
  • The EGR Valve Pintle Position sensor.
I suggest that you concentrate on that one first. Try this:

Important:

Be sure to inspect PCM and engine grounds for being secure and clean.


Check for the following conditions:
  • Poor connection at the PCM. Inspect connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
  • Damaged harness. Inspect the wiring harness for damage.
  • If the harness appears to be OK, observe the MAP display on the scan tool with the ignition ON, engine not running while moving connectors and wiring harnesses related to the following sensors. A change in the MAP display will indicate the location of the malfunction.
    • The TP sensor.
    • The MAP sensor.
    • The EGR valve.
    • The fuel tank pressure (VIN K only).
Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

For more info Google "P1635 GM"
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Old 11-17-2013, 10:28 AM   #5
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If you're anywhere in So California, I would strongly recommend taking it to Redlands Truck & RV. They have many experts there and you will be paying for the correct fix and not hit & miss troubleshooting. They are one of the most highly respected Workhorse service centers in the country with many satisfied members on this forum for a decade.

If you want to do some DIY, I saw 8.1L erg valve for $57 and Throttle Body for $188 shipping included on Ebay.

Good luck,
Bill
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Old 11-17-2013, 10:44 AM   #6
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One marginal spark plug?
One plug wire that got a bit crispy?
It runs on fuel, spin, and spark.
Sometimes ya gotta look for the obvious first. ;-)
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Old 11-17-2013, 11:54 AM   #7
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Quote:
Originally Posted by linda7915 View Post
[LEFT]When driving in traffic, pulling away from stop, accelerating on freeway onramp, etc. at about 25-30 mph, the engine misses, sort of like a loping thing, then it runs fine once it gets over 30. It also idles just fine. We took it to the Chev/Workhorse dealer and he put the scanner on it. Found codes P0404 (Exhaust Gas Recirculation Circ Range/Perf), P1514 (Air Flow to TP Sensor Correlation Hi) and P1635 (5 Volt Ref Lo).Unfortunately, he can't figure out the underlying issue and is suggesting a new throttle body, followed by a PCM if that doesn't solve it. He can't say specifically what is wrong and if the $800 throttle body (plus labor) doesn't fix it, it can't be returned. NO! Not a good solution, at least not at this point.
.........
Glad to hear someone is not paying for a "guess".
That's what I would tell anyone I'll pay you to fix it, but not to guess or take a shot in the dark.
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Old 11-18-2013, 06:52 AM   #8
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I had similar issues going up hills (i.e., higher rpm under strain like your accelerating on to highway) and it was plug wires. Because of the high heat in our engine compartments that damages plug wires internally many of us have had this problem. I did not have any codes though. I would clear your codes (stop at autozone etc and they will read and or clear your codes for free) and see if they come back. High quality plugs wires are a must any way in these rigs because of the heat issue. I also changed out the spark plugs at the same time. Good Luck. Greg
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Old 11-19-2013, 10:44 AM   #9
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I would do basic maintenance first. Replace the spark plugs and wires, new fuel filter and air filter. Clean the MAF sensor (with MAF spray cleaner). Clear the codes, then if the problem is still there, start troubleshooting the problem knowing you have known good basic components.
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Old 11-25-2013, 04:05 PM   #10
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Yep...plug wires. BTDT.

Get a set of the taylor racing wires and use the stock shields. They recommend not using them but I burned the first set that way, so now they get the metal shields. No problems for the past 15K miles.
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Old 11-25-2013, 08:02 PM   #11
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Issue update: We brought the MH home from the dealer ($210 later, no fix, just labor to look). We took a short trip this weekend. Started out with no problem, but once the engine warmed up, it did the same as before... loping (or bucking) at 20 - 30 mph. About 15 miles out, it started doing it at 55-60 mph. Once it got past about 5 more miles, it smoothed out, totally.


When we left on Sunday, it was ok while engine was cool, but about 10 miles out, we were going about 55, slowed to about 50, and it died. Pulled over, gave it about 30 seconds, and it started back up. When it died, the Service Engine Soon AND the Reduced Engine Power lights came on. Once we got going, the REP light went off, leaving the SES light on. Got home, stopped and restarted, SES light was off.

Husband doesn't want to tackle it so we took it to a local Chevy mechanic. New codes don't include the EGR. He thinks the MAF needs cleaning or replacing. He's going to KISS (keep it simple, ..) and clean it. If that doesn't work, next step will be replacement, probably. Fortunately, that's not an super-expensive part. Will pass along what we learn. Appreciate all the input.
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Old 11-25-2013, 10:47 PM   #12
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Just have them pull the plug wires... PLEASE!!

I'm betting my bottom dollar one of them will crumble. The 8.1 is absolutely famous for this. I chased all that crap too, was so sure it was a fuel pump, even insulated the fuel lines thinking vapor lock. I was so sure it wasn't the wires because I had just replaced them with $60 Taylor race wires. But I pulled them anyway and sure enough, at least a couple were burnt. Problem fixed.

Was doing EXACTLY as you describe. Sounded just like fuel starvation.
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Old 11-25-2013, 10:59 PM   #13
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Had a similar problem a couple months ago. Very intermittent. Plug wires cured it.

Prior to that I had problems climbing mountains and cleaning the MAF and replacing the air filter cured that problem.

So you are on the right path with the MAF but I'd also go for new plugs and wires.
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Old 11-26-2013, 12:12 AM   #14
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I agree with the other posters that your problem could be plugs and wires even with the low mileage. However, it is also possible that the problem is related to two of the problems on the attached web page, carbon buildup, and vacuum leak.
Problems With the Throttle Body on the Chevy 8.1 L V8 | eHow
You may want to get a code scanner. I bought one at Harbor Freight, have used it on my 05 GMC Yukon XL. I like it because it reads real time and you can see the readings change while diving.

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