[Diy_efi] Detuning Motorhomes

[Aaron]

More that didn?t make it to the list.

From: Aaron [mailto:aaron at creativeoverdrive.com] 
Sent: Tuesday, January 18, 2011 11:12 AM
To: 'diy_efi at diy-efi.org'
Subject: RE: [Diy_efi] Detuning Motorhomes

Up today ? heat and electronic placement

Background on some of my antidotal experience. I was a mechanic for most of the 90?s. Cars, light trucks and motorhomes. Then I went back to college and got a Mechanical Engineering degree. Anyway, during the late 80?s and early 90?s, GM like to place electronics and relay in the back corners of the engine compartment on the firewall. After a few years is was noticed those components were having a high rate of failure. As the story goes, GM did a temperature study and found that those back corners were the hottest place on the firewall due to a lack of air flow. I took that story to heart and try NOT to mount things in that area, especially in the GMC motorhomes. They have the plastic inner fender that makes a huge dead air pocket to heat soak electronics.

16. Get engine vents. They mount under the belt line, above and behind the front wheel well and before the body seam. There are several styles to choose from. Stainless Steel, Paintable plastic, aluminum and even chromed. They let A LOT of heat out of the engine compartment, which makes the driver and passenger floor cooler and keeps the relays and electronics happy.
17. ECU under the OEM passenger seat or along the passenger side wall. This position just works out well and most kits plan the harness length to get you there. It makes a great place for your co-pilot to sit with  the Laptop when you?re making changes to the fuel / spark maps. Most people cover the hole they cut in the floor to seal it back up. And NEVER EVER run wires under the carpet to get somewhere close. The guy troubleshooting your installation will thank you.
18. Relays, ETC module and MAP sensor typically get mounted to the fire wall onto the aluminum frame surrounding the access door. I like to move them out of the way a little by shifting them more under the passenger seat.
19. Make a new power distribution center !!! Our coaches have only one spare IGN (ignition) terminal in the OEM fuse block and they are always used by some add on or another. I HIGHLY recommend using that one IGN terminal to power a 50 amp relay and circuit breaker from the BAT (battery) terminal to create a IGN distribution center. From there you can get reliable power to the other add on fog lights, air horns, electric dash fans, light up dancing hula girls, etc. If you look under the passenger front cover / access door, there is typically a small hole with the blower motor wires going thru it. I run the one IGN wire in that hole and mount the new IGN relay, circuit breaker, fuse block and other relays on the aluminum plate next to the OEM BAT terminal.
20. Check those grounds. There should be a braided ground strap from the steel frame to the transmission mount at the back of the engine compartment. There is also a braided ground strap next to the coach battery that connects the steel frame to the aluminum body structure. The negative battery cable should connect the battery to the engine block AND with a smaller wire to the frame or aluminum body. If any of them is missing, put them BACK!
21. Keep the MAP sensor close, but not too close. I like to put the map sensor on the aluminum frame on the passenger side of the access door frame. It?s close to the TBI so the vacuum hose is short. It may be over the exhaust manifold, but the air flow is good and seems to keep it cool. I don?t like the idea of mounting it to the air cleaner housing for both heat and vibration reasons.
22. For the GM based systems, put the ?Check Engine Light? were you can see it driving. One of the instructions have you mount an aftermarket light bulb at the base of the passenger seat for the Check Engine Light. I typically run extra wires and mount it on 

By the way, I need to give credit to the gentlemen who prototyped the first Howell TBI kit back in the late 90?s. He did a very good job and it is a great starting point. They GMC community has also done a great job of trying new ideas for TBI systems. I?m not sure I can take credit for more than one or two of these ideas. I?d thank them all in person, but I just don?t know who they all are.

Sent: Monday, January 17, 2011 3:03 PM
To: 'diy_efi at diy-efi.org'
Subject: RE: [Diy_efi] Detuning Motorhomes

Next up ? Exhaust.

11. Beware of the OEM exhaust manifolds. I dislike the OEM cast manifolds with a passion. Gee where to start. The casting crack or warp under the two center ports. The center bolt on the top makes it worse. If you tighten the center top bolt, it pulls the bottom out and making a leak. The passenger side is even worse. The notch GM created to clear the oil filter mount cuts the cross section of exhaust flow in half. On the 403 CID, the notch cuts the flow even more. Then if you surface the manifold to make it flat again, beware of the driver side dipstick tube. It runs between the manifold and the head. If you surface too much, then you?ll crush the tube when you install the manifold or the tube holds the manifold out to create a nice load leak. 
12. Get HEADERS. The steel plate is thicker and more sturdy to prevent exhaust leak. The dip stick tube will no longer get heated to the point of failure or crushed by the OEM manifold. The flange at the collector can be set up to use the same ball type gasket which makes getting the y-pipe to fit much easier. All is not roses however. The headers do seem to make the engine compartment hotter and some customers also claim they are louder. I agree with that, but feel the benefits in exhaust gasket maintenance and performance increase only justifies their use. 
13. O2 placement needs to be as close to the engine as possible. On the OEM pipes and Manifolds I like the Driver side pipe directly after the manifold to pipe gasket. It?s high on engine which keeps it out of the rain water and weeds. On the headers, I?ve installed sensors in the header collector and on the pipe directly behind the collector. Both locations work equally well, but a ~30 away from the exhaust port, so I also recommend heated O2 sensors. With headers, I typically run the O2 on the passenger side, because the starter transmission kick down solenoid wire is already running there. 
                Yes that would be one Sensor in only one bank of a V8. There is an assumed risk of not monitoring the second bank. But with the original style manifold, one injector feeds both banks. So in the event of an injector or other failure, the manifold should present the issue to both banks. The collector at the end of the Y-Pipe is also much too far away for an O2 sensor. ~6 feet away from the exhaust ports.
14. Seal all the exhaust leaks before and short after the O2 sensor. As most know, an exhaust leak before an O2 sensor may suck in fresh air in between exhaust pulses. I?ve found that on this big blocks exhaust leak within 1.5 feet after the O2 sensor will also suck in fresh air at idle.
15. 3? exhaust from the Y-Pipe back. I?ve always been impressed by the seat of pants change in performance when going from 26 feet of ?2.5? exhaust pipe to ?3? and two quality mufflers. 

Back to Intake Manifolds.

General information.
- As our coaches age, the rubber supports that keep the aluminum structure off the steel frame begin to crush or have fallen out. Putting them back in or replacing them not only makes the coach quieter and better handling, but has an unusual side effect. It raises the floor up off of the air cleaner housing. If you look closely at the engine access door / floor, you?ll see where the OEM air cleaner has been rubbing on the wood. I typically get out the router and remove more wood on the access door and then replace or update the insulation on the steel  plate with thermal bubble plastic or thermal foam. Be sure to remove the back middle screw of the steel plate before you start up the router. It?s really hard on the router bit.
- GM and Chrysler have plastic ?Top Hats? from later model cars and trucks that can be used on the TBI that allow you to move the air filter off the top of the engine.


More later on heat and electronic placement.
By the way, stop me if you have specific questions.