I had a Jasper remanufactured 5.8L engine installed in my 89' F-150 last year in the place of the old 5.0L and it ran pretty good for 8000 miles, but a couple weeks ago, I decided to replace to engine computer (I've been running the new engine on the old computer). It seemed to run alright on new computer, but with little increase in power. We drove it around for about an hour and we did notice some tapping sounds at high rpms. The next time I drove it, i got about 5 miles and the engine blew up. I was told by the guys at the shop that "it blew the piston out of it." I'm not sure exactly what they meant by that, but Jasper is sending me a new engine. My question is why did it blow? My theory as of right now is that I should have adjusted the ignition timing after I installed the new computer. I think I had the timing advanced a little to allow it to run with the 5.0L computer and I neglected to change it after I installed the new one. Does that sound right? Any other theories?

 

what ecu did you put in? what was your oil pressure like? what was your timing set at?

 

It would proably take a lot of timing to do that and, there would have been detonation or other symptoms before she blew if the timing was to advanced. I'm running 16 degrees advanced base timing and i can't even make my truck detonate, hesitate or buck under load.

kemical can proably help a little more than i can but you got to give us a little more to go on. There had to be some other signs besides it just started tapping at higher rpm's after about an hour of driving with the new ecm.

 

I'm fairly sure the oil pressure was fine, and i have no idea what the timing was set at because I don't have a timing pointer. We've had to set it "by ear" ever since we installed the 351. After the shop tore it down they found out the piston was cracked. A piece had actually cracked off and you could see the top of the ring.

 

you should not try to time an efi motor by ear. get a timing light they are not expensive and will be way more accurate.

 

Yeah I know, I said I haven't been able to find a timing pointer that will fit it. I have a timing light

 

why wont the stock pointer work?

 

He said he doesn't have one, but I don't understand why he can't find one....


They're everywhere. Get a 351 timing pointer, do you have markings for degrees on your damper? Put the #1 cyl on TDC, make sure the damper/timing pointer are aligned at 0, put the timing light on and make sure the timing goes to 10 degrees w/ the SPOUT connector disconnected.

I'm willing to bet that the new computer ran your engine lean. That would explain the power increase and later the demolition.

 

Ok, I finally got a new pointer installed; I had to do a little fab work on it to make it fit because the thermactor pump was in the way. Anyway, the timing is set right now, and the engine sounds great at idle, but it still doesn't feel quite right when I drive it. I'm pretty paranoid right now, though, that its gonna blow up again, so maybe I'm just imagining things. It's also running quite a bit warmer than it was before, but I guess that's because it's burning more fuel, I'm not sure. It's well within the normal range, but i think i'm going to get a new temp sensor just to be on the safe side. Also, when i test drove it, I got a weird, "pop" noise that sounded like it came from the air intake. It only happened once, when I let off the accelerator, kinda like a backfire, but not as loud. I had that problem once before, but it went away when I replaced the idle air control valve and adjusted the timing, I think (i don't remember exactly)


The old computer was making it run lean, the new one should fix that, right? The old one was for a 302, the new one is for a 351. I think the problem was ignition timing because when i checked the timing today, before I put the new computer back in, it was running at about 30 degress BTC (because it had been set "by ear" on the old computer) Wouldn't that be enough to make it blow at high RPM?

 

The stock pointer would work if i had a stock setup, but I did an engine swap and now I have a mix of stock 302 and 351 parts along with a bunch of aftermarket performance parts. Thats why I'm having problems.

 

As long as you used the same year's parts, the timing covers were the same between the 302 and 351. Ditto for the balancer. As for why your motor blew up, sounds to me like a combination of too much timing and too lean fuel mixture. What other "performance parts" do you have in there? Do you have a Mass-Air EFI or Speed Density?

 

Is this 351 engine a completely stock caliber engine? Or does it have a little more performance than a stock engine?

If you're running a speed density system, you have to be careful about how much airflow is going through the engine as well as what the computer is expecting to see.

A 302 and 351 computer for speed density are basically not interchangeable. The computer is pre-programmed to run the motor it was setup to run. The 351 flows more air than the 302 so the computer needs to know that. If you run a 302 computer on a 351, that computer still thinks it's trying to run a 302, and will not run the motor 100% correctly. It may run the engine, but most likely not enough to do so correctly.

If the 351 you've got now flows more air (more hp) then the stocker, then the SD computer needs to be adjusted to compensate as well.

 

Don't rule out a vacuum leak in the system somewhere. Any unregulated airflow can be disastrous in any engine no matter how well built it is. If you have never checked all of the vacuum lines and all of the vacuum operated devices in the truck you need to.

Check and fix the free stuff first before you do anything.

 

Well, I got a JEGS pointer and had to cut it to make it fit, cause the thermactor pump was in the way, but i got it working and have the timing set right now. As for the harmonic balancer, I had a few people tell me they were weighted differently, so that was replaced right after the swap.

I'm still running a SD system, and probably will be for quite a while. The engine itself is all stock except for the intake and thats a Edelbrock Performer with a K&N filter kit attached to it. The throttle body, water pump, radiator, and injectors are all the same stock parts i was using with the 302. The distributor is stock with an MSD cap and rotor and I'm using an MSD Blaster TFI coil. The spark plugs are Autolite double platinums gapped at .055.

I'm pretty sure now that the engine blew up because of the timing (prolly about 20 BTC), but I don't think it was running lean because I had the correct computer installed when it blew up. see it happened right after I installed the new computer.

 

I'm pretty sure i don't have any unregulated air coming in, unless it's leaking around the manifold. I made my own vacuum tube harness and all that is hooked up correctly. I am worried, though, that the computer might be confused by the 302 throttle body, because I'm told the 351 has a slightly bigger one. I saw that you can buy oversize throttle bodies, though, so maybe that calculation is made correctly regardless of throttle body size.