texaswrrr Report post Posted May 14, 2015 I have an 2007 Workhose chassis with 8.1 engine. It started back firing at 44,000 miles so I changed the standard wires to high temperature wires and at least 3 of old wires were burned. This improved the condition but did not cure it. Next I installed new spark plugs again improved but did not cure. It back fires, normally, one pop on down shift and one on up shift 5th gear to 4th gear (6 speed tranny). On down shift into 3rd gear on steep hill it is constant popping and I drop cruise and go manual throttle to minimize problem. Do not have any engine lights or codes. I can see the back fires on computer program but just as a blip with no info. I do most of my own service but at total lose on this one. Share this post Link to post Share on other sites
dickandlois Report post Posted May 14, 2015 texaswrrr, Welcome to the Forum! You did not mention that you had a check engine light. So I'm thinking you may have a Cam sensor issue-if you 8.1 starts and runs rough. Then if you turn off the engine, restart and it runs smooth. You most likely have a cam sensor issue. You did not mention the engine acting like you turned off the key and back on while driving or a bucking sensation, that could indicate a distributor sensor issue. You might want to have you mechanic run engine diagnostic to see if there are any codes present and check the engine timing information or if there is a failing ignition coil. The 8.1L has a coil for each plug that you would have noticed when installing the new plug wires. The third item that you might look into is the throttle body and the mass air flow sensor, what is the condition of the air cleaner? I'm leaning towards fuel air mixture issue or timing problems. With only 44,000 miles it should not be related to timing chain and gears, but stranger things have happened. Rich. Share this post Link to post Share on other sites
texaswrrr Report post Posted May 14, 2015 Rich Thanks for your speedy reply. I have NO check engine light "on" and no codes showing when checked with a reader. When its goes into high RPM (above 3000) the back firing is so severe that some bucking is felt. A the lower RPM's it is just annoying. Engine runs smooth every time it is started. Air filter is new & clean. Is there any way to check the coils for which one to change or just buy 8 new ones and install them. I now have 60,000 on the engine so has been a continuing problem for a while! Thanks for your input. texaswrrr Share this post Link to post Share on other sites
jleamont Report post Posted May 14, 2015 texaswrrr, it sounds to me like the ignition system is cutting out then back on to get a back fire, while the fuel system continues to deliver fuel thus the reason for the back fire. Seems like I said above fuel continues to spray but the spark drops off and comes back unexpectedly. I just got a response back from a friend that works at a GM dealer as I was typing this, he told me to tell you to look for broken supply wires to the coil at each coil (12v power and ground) and inspect the connections at the other end of those at the computer. Also he recommended to run it with a diagnostic computer connected and see what cylinder is dropping off when you experience the problem, that will help isolate which cylinder is of concern, I explained you may not have the ability to do so. Also they have wiring concerns with the main harness chaffing that feeds the engine on a truck chassis, its always near the radiator area where they chafe, he is not sure on a Motorhome chassis, GM also has wiring connection problems at the coil plug and at the ECM. I would follow that harness from start to finish (Computer to engine coils) If the wiring looks good and all connections look good replace that coil if you can isolate it down to a specific coil. Hope this helps and you have enough space to follow that harness. Good Luck Joe Share this post Link to post Share on other sites
bm02tj Report post Posted May 15, 2015 If the electronics do not show anything it could be a bad valve guide, lifter or lobe on the camshaft Share this post Link to post Share on other sites
waypeg65 Report post Posted April 17, 2018 My 8.1 Engine is also backfiring under load. I am trying to find the GM Dealer is in PA. jleamont posted that he has a friend that works at a GM Dealer and his friend it familiar with the problem. Any information is appreciated Wayne Share this post Link to post Share on other sites
dickandlois Report post Posted April 18, 2018 Wayne, Send a PM to Joe. He is town, just exchanged some information with him. Rich. Share this post Link to post Share on other sites
obedb Report post Posted April 18, 2018 New members may not know how to send a PM. Share this post Link to post Share on other sites
waypeg65 Report post Posted April 23, 2018 How do I Send a PM Wayne Share this post Link to post Share on other sites
wolfe10 Report post Posted April 23, 2018 7 minutes ago, waypeg65 said: How do I Send a PM Wayne Click on the member's name on the left side of their post. On new page, click on "Message" to send a Private Message. Share this post Link to post Share on other sites
