300 six, dead hole under 4k rpm
#1
300 six, dead hole under 4k rpm
Hey all, I'm really scratching my head here... I have an '86 F150 2wd on Propane with an '89 300 6cyl, Mazda 5spd and T-case in it. The problem I am having is anywhere under 4000rpm it runs like there is a dead cylinder, after that it starts to fire and smooths out, at idle it looks like its going to jump out of the mounts.
When I got the '89 that the engine came out of it ran the same way but being on gas it was running VERY rich, no sensors seemed to test right etc. but showed no codes. We decided it could be a faulty ecu. and stripped the truck. As of now its in my '86 with EFI Intake and exhaust, the '86 DS2 distributor, along with the new plugs wires etc from the old engine...
Tonight I went out and pulled the upper intake, valve cover and plugs. No bent pushrods, and everything moves nice. The compression on cyls 1,2,4,5,6 is at 160psi and cyl 3 is at 170psi. I'm now lost...
When I got the '89 that the engine came out of it ran the same way but being on gas it was running VERY rich, no sensors seemed to test right etc. but showed no codes. We decided it could be a faulty ecu. and stripped the truck. As of now its in my '86 with EFI Intake and exhaust, the '86 DS2 distributor, along with the new plugs wires etc from the old engine...
Tonight I went out and pulled the upper intake, valve cover and plugs. No bent pushrods, and everything moves nice. The compression on cyls 1,2,4,5,6 is at 160psi and cyl 3 is at 170psi. I'm now lost...
#3
Have you sprayed for intake leaks? My guess is that there's a massive intake leak at one of the runners, and it isn't till 4,000 rpms that the mixture richens enough for it to fire.
That's just a guess though, but it sounds like you've checked everything else out.
I agree with rustywheel, try to find which cylinder it is that's causing the issue. Fire it up, then pull each plug wire off (one at a time) untill you find one that doesn't change how it runs.
Sam
That's just a guess though, but it sounds like you've checked everything else out.
I agree with rustywheel, try to find which cylinder it is that's causing the issue. Fire it up, then pull each plug wire off (one at a time) untill you find one that doesn't change how it runs.
Sam
#4
I'll give the plugs and vac leaks a try again when/if the snow lets up. I had the intake off the engine when I put it in the truck (original plan was to run the efi exhaust and the stock carb intake) so all the gaskets are new.
Any thoughs on doing a leakdown test at this point or would it be worth the work?
Any thoughs on doing a leakdown test at this point or would it be worth the work?
#5
Hey all, I'm really scratching my head here... I have an '86 F150 2wd on Propane with an '89 300 6cyl, Mazda 5spd and T-case in it. The problem I am having is anywhere under 4000rpm it runs like there is a dead cylinder, after that it starts to fire and smooths out, at idle it looks like its going to jump out of the mounts.
When I got the '89 that the engine came out of it ran the same way but being on gas it was running VERY rich, no sensors seemed to test right etc. but showed no codes. We decided it could be a faulty ecu. and stripped the truck. As of now its in my '86 with EFI Intake and exhaust, the '86 DS2 distributor, along with the new plugs wires etc from the old engine...
Tonight I went out and pulled the upper intake, valve cover and plugs. No bent pushrods, and everything moves nice. The compression on cyls 1,2,4,5,6 is at 160psi and cyl 3 is at 170psi. I'm now lost...
When I got the '89 that the engine came out of it ran the same way but being on gas it was running VERY rich, no sensors seemed to test right etc. but showed no codes. We decided it could be a faulty ecu. and stripped the truck. As of now its in my '86 with EFI Intake and exhaust, the '86 DS2 distributor, along with the new plugs wires etc from the old engine...
Tonight I went out and pulled the upper intake, valve cover and plugs. No bent pushrods, and everything moves nice. The compression on cyls 1,2,4,5,6 is at 160psi and cyl 3 is at 170psi. I'm now lost...
By 1986 (pre 1984 for california emissions, 1984 and newer for 49-state emissions), the 300 was using a computer-controlled carburetor. So if you've got a DS2 distributor from a 1986, and the timing is controlled by vacuum lines, then you've got the wrong distributor. And, the wrong distributor was on the 86 unless someone performed a COMPLETE duraspark 2 swap on that motor.
You said the motor is an 89', which would be a computer controlled 300-6, but you put the Duraspark 2 distributor from the 86 in the 89 motor and your STILL running it with the computer?
That's your problem. If it's a 1989 motor with all the computer associated hardware and it's electronically throttle-body injected with a carburetor distributor, the computer can't control the ignition timing and makes the truck run like !%#@ because the computer is in what would be known with the computer controlled carburetor version of this motor as "limp-home" mode. It might not be as severe as it would be with a computer-controlled carburetor that was trying to run with vacuum advance, but it's the same case even though your using throttle-body injection instead of a computer controlled carburetor as was the case in 84 to like 87 motors.
Start by getting the 1989 distributor for your motor, the associated wiring harnesses, and hooking it up and setting everything back right with a timing light so the computer can control the ignition timing.
Then, pull codes from the OB1 computer and see whats going on if there are any other problems.
The other issue is that your running the motor on propane. These motors were designed for unleaded gasoline.
#6
Ok, to clarify on the truck and engine. The truck is an '86 with factory NON EGR, non Catalyst emissions so I assume plain Duraspark then as it was sold for an alternative fuel conversion, no feedback system either. The '89s has everything in place but is running the '86's electrical/timing and an Impco 225 mixer bolted in place of the throttle body.
Running the I6 on propane should be a non issue, the distributor in the engine is recurved for said fuel etc. Only difference between the '86 and '89 long blocks should be 8.0:1cr vs 8.9:1 cr
I will get it fired up tomorrow and start hunting for vac leaks and see what turns up.
Running the I6 on propane should be a non issue, the distributor in the engine is recurved for said fuel etc. Only difference between the '86 and '89 long blocks should be 8.0:1cr vs 8.9:1 cr
I will get it fired up tomorrow and start hunting for vac leaks and see what turns up.
#7
This really sounds like 1 of 2 possibilities. Could be an issue with a vacuum leak in 1 runner (cracked intake, bad gasket, injector hole seal leaking, ECT) or a problem in the ignition system (bad plug, wire, cap, or internal dist issue {less likely, since it followed engine even with dist swap}).
A far fetched sounding, but plausible cause, could be an intake runner that has something restricting it severely.
Have you left the EFI injectors in place to plug those holes, or replaced them with something else? Either way, your issue could be right there......
A far fetched sounding, but plausible cause, could be an intake runner that has something restricting it severely.
Have you left the EFI injectors in place to plug those holes, or replaced them with something else? Either way, your issue could be right there......
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#8
I left the injectors and fuel rail alone yup. It seems to be better now, the egr valve was cracked(also stuck partially open), the one ear snapped off when I bumped it against the intake.
There are other problems that are related to the length of the vapor hose to the mixer now so I might just mod the exhaust manifolds and run the log intake. At least its idling smooth though.
There are other problems that are related to the length of the vapor hose to the mixer now so I might just mod the exhaust manifolds and run the log intake. At least its idling smooth though.
#9
#10
Seems my post last night didn't work. The egr valve was a suprise for sure, especially when it came off in 2 peices...
As for the fact that it is running on LPG, the biggest difference is that a Vacuum leak will affect how the gas valve in the mizer works as well as how well the fuel is drawn from the vapourizer. It for sure runs better but if I get the chance tomorrow I'm going to swap the stock log intake back on and see how it works.
As for the fact that it is running on LPG, the biggest difference is that a Vacuum leak will affect how the gas valve in the mizer works as well as how well the fuel is drawn from the vapourizer. It for sure runs better but if I get the chance tomorrow I'm going to swap the stock log intake back on and see how it works.
#11
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