Hello all, I know there are plenty of threads on here that may help and I have begun to look through them for some answers. 89 f250 7.5 efi, manual trans. Rebuilt the motor, just finished or so I thought. headers, duals, I cut out the cat ( it was garbage anyways) no smog pump, cut out the baffles on the intake hoses, new gaskets all around, honed the cylinders and new rings, new distributor, new plugs, wires, upgraded cam ( SUM 3501 ), new springs and lifters. Also replaced the fuel pump relay, high pressure pump on the frame rail, pressure regulator, and replaced the eec relay ( I thought it was bad but turned out that I forgot to ground it ) Anyway, I'm sure I forgot something. Problem I'm having is when I accelerate. It feels and sounds as though I'm down a cylinder or two. its just bogs down super hard and chugs until I get up to speed. At which point it either stops doing it or my exhaust is so loud that I cant hear that its doing it anymore. Doesn't seem to have that problem at highway speed. 45 and over. Idle sounds pretty ok. Anyone have any ideas? I'm planning out replacing the map sensor, ignition control module, and possible the TPS and Ignition coil. Though I don't think the coil may have much to do with it because I have spark. Compression tested fine. I haven't checked fuel pressure yet, but am going to after work today. Any other spots to check out? Or any ideas on what may be causing this issue would be appreciated. Sorry for the long post, just didn't want to leave anything out. Thanks

 

Ok. Checked fuel pressure. 40 key on engine off and steady 32 at idle and it jumps to 40 when rev. Unplugged map when idling increased idle speed by a few hundred ( not sure what that means) and unplugged the iac and it died, so I think that means it's working. The only think I can think of next is maybe a vacuum leak at the egr? Would that cause this issue?

 

What's the vacuum in. indicated with a test gauge installed on the intake man. tap at idle? Run smoother when cold? More of a flat throttle or lag,, or is it a misfire? Addding timing advance seem to correct the condition?
That 3501 doesn't look to be a good low end/torque cam.

 

It definitley runs better cold. Night and day difference actually. I'll have to check the vacuum in tomorrow when I have a day off. When she's acting up it's hard to tell if it's a misfire or fuel pressure issue. When it's real warm or if I've been driving for awhile and turn the engine off it's real hard to get her started. Will crank and crank and crank with spurts of ignition every now and again. Tfi? Thanks for the reply. I appreciate it

 

Looking at those cam specs it's more of a mid/ top end cam so idle quality and low end performance will suffer.
I built my 69 Firebird Ram Air III (335 hp) and had been sold a GTO RA 345hp cam. Running the stock rockers/springs, carb and distributor it ran 'ok' cold but idle wasn't really stable, more so heated up,, vacuum was low, and advancing the timing made for better conditions overall but would crank lock turning it over heated up. Restarts were some work, It wouldn't just 'crank to idle' when warm without adding in some extra throttle to coax it to run.
Setting the timing (or trying) to spec had about the same the topic results.
Off idle/2000 and above it had no issues, but being a 4sd car bottom end pull is perfered for my needs.


Was the cam degreed on install?
Because my stock timing settings produced poor idle conditions and general lacking throttle response, thought possible new timing set was mis marked or some offset. Prior to the correct cam going back in rechecked the indexing and it was off a few degrees. Ordered up a adjustable timing set ( just in case) and the correct RA cam, check the index and it was fine without gear adjustment. Car runs great, but low vacuum with power brakes in street conditions,, 4sd, didn't work well..

 

I knew i would have some issues with idle and loss of low end. She already had tons of low end so I didn't think I'd mind too much. And even now when she runs at her best shell pull me to the back of my seat no problem. I kind of degreed the cam. I didn't use a wheel but I set #1 valves closed, checked rotation of crank and cam together to make sure that all valves were opening and closing properly and in order on each cylinder and then also checked rotation of rotor to make sure everything worked in sync before I put her together. Maybe not the best way or easiest way to do it. Alot of room for error there on my part. Advisable that I should tear into the front of the motor and degree it with a wheel?
To add to that, I did notice some of the same issues you were having the other day while she was all warmed up. I had been driving her around a bit. Crank lock and I had to coax her to start with some throttle. Took a little while for a start though. I kick myself in the *** now for not changing the timing gears but I was under the impression that the timing was straight up already on 89s but I may be mistaken.