wes flaharty Posted October 2, 2022 Share Posted October 2, 2022 Hello,I have a 1992 e7 vmac that starts good and runs fine but when you drive for a few miles the vmac light comes on and it shuts itself off however it will start right back up and you can go a few more miles. This truck has had a lope of about 200 rpms at idle ever since i have owned it, I put a used vmac and ficm in it about 1 year ago for an issue where it would not start. any help appreciated,thanks Quote Link to comment Share on other sites More sharing options...
topo Posted October 2, 2022 Share Posted October 2, 2022 what is a vmac and ficm ? Quote Link to comment Share on other sites More sharing options...
Onyx610 Posted October 2, 2022 Share Posted October 2, 2022 Vehicle Management And Control and Fuel Injection Control Module Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted October 2, 2022 Share Posted October 2, 2022 I soil pressure above 10 PSI? Is the flywheel sensor wiring in good condition and plugged in good? That is the RPM/TDC sensor.. make sure the duetch connector at the governor housing is connected good, and that there are no loose pins in either side of that plug. when you put that plug back together, make sure it is clipped into the holder and wire tied in place.. jojo Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted October 2, 2022 Share Posted October 2, 2022 You can do a wiggle wire test while it is running. You can wiggle the RPM/TDC wires and plug, and the injection pump connector, and the FIC/VMAC connectors, as well as the acc. relay behind the dash, to see if any of them shut the truck off.. jojo 1 Quote Link to comment Share on other sites More sharing options...
wes flaharty Posted October 2, 2022 Author Share Posted October 2, 2022 Thanks for the replies, the oil pressure is 25 at idle(at 180),the wiring all looks good and I unplugged the deustch connector at the pump and everything seems tight. I'll try a wiggle test tomorrow. I ran 12 volts to the fuel shutoff and that keeps it from shutting off but the vmac light still comes on and it won't except throttle. Any other thoughts on the lope, it has always had this since I've owned it. If I can't get this thing figured out I'd like to make it mechanical or drop a mechanical engine in. Thanks Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted October 2, 2022 Share Posted October 2, 2022 I am not very smart about the inner workings of the injection pump, but I would consider a weak spring inside the pump/ or rack actuator.. can you hook a fuel pressure gauge to the input of the secondary fuel filter to see if it fluctuates, causing the lope? or while it lopes? Maybe to see if it a lift pump issue.. My GUESS would be if fuel pressure is steady, then there may be an injection pump issue.. There's a few really smart old timer's on here that know the inside of those pumps like the back of their hands... I hope they join in.. as far as the throttle, did you check the condition of the TPS at the pedal, as well as wear on the roller under the pedal. Lot's of dirt off of work boots gets in there... Im trying to keep it simple, rather than loading a parts cannon, Jojo Quote Link to comment Share on other sites More sharing options...
wes flaharty Posted October 2, 2022 Author Share Posted October 2, 2022 I'll check fuel pressure, I did replace the throttle pedal about two years ago because the old one had a lot of wear on the roller but it made no difference in the lope. I have 5 other R models that are all mechanical and this one has me stumped. Seems the local mack dealer does'nt have anyone with the knowledge on these old vmac engines. If I wanted to make it mechanical is it as simple as an injection pump and linkage? Thanks. Quote Link to comment Share on other sites More sharing options...
Joey Mack Posted October 2, 2022 Share Posted October 2, 2022 yes, but there is also fuel timing changes that need to be done... I only did 1 about 6 years ago, so i'm rusty.. hopefully you fix this one.. Do you have a mechanical Robert Bosch pump kickin around ? since you have a few others, converting would be easier, because you have examples to look at... 👍 jojo Quote Link to comment Share on other sites More sharing options...
wes flaharty Posted October 2, 2022 Author Share Posted October 2, 2022 I don't have any Robert Bosch pumps laying aound, I have an Ambac off of an E6 300 but I think That's a 3 bolt mounting. I have a good running E7 400 Mechanical in a project truck that i can use if I have to. Hopefully I can get this thing figured out. Thanks 1 Quote Link to comment Share on other sites More sharing options...
topo Posted October 3, 2022 Share Posted October 3, 2022 Your first post reminded me of trouble I have had with fuel lines when using braded fuel lines like Aeroquip the very thin liner inside the hose would separate and collapse and seal the hose closed when driving because the pump is pulling more fuel after it stopped running and not drawing a suction it would open back up and restart and run ok till the pump suction increase would collapse the liner again . the place where this would happen the most is if the fuel line was inside the frame where the exhaust was near the line . Quote Link to comment Share on other sites More sharing options...
Dirtymilkman Posted October 3, 2022 Share Posted October 3, 2022 I think Joey is on the right track with the injection pump. The shutdown might be a separate problem from the lope. Will prolink or something similar say why the light is coming on? Does the override switch stop it from shutting down? Coolant level sensor, temp sensor and oil pressure sensor are the three that can shut engine down. Motor only needs crank sensor to stay running otherwise. Something in those circuits is triggering the light. Quote Link to comment Share on other sites More sharing options...
fjh Posted October 3, 2022 Share Posted October 3, 2022 14 hours ago, wes flaharty said: I don't have any Robert Bosch pumps laying aound, I have an Ambac off of an E6 300 but I think That's a 3 bolt mounting. I have a good running E7 400 Mechanical in a project truck that i can use if I have to. Hopefully I can get this thing figured out. Thanks So heres what I suggest first ! Next time this happens don't touch a thing ! How ever check to see if the heater fan still works! If not you have a weak accessory relay !Top of the list is check the codes! post what you find! what your purposing to do would help to have a donor truck or you have donor engine or buy you injection lines linkage bla bla a bunch of subtle stuff you don't think about! 1 Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.