What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

top end breaking up

B

big bearded bastard

Registered Member
Joined
Apr 26, 2011
Posts
17
Reaction score
0
Location
NE florida
i have a 89 gmc jimmy with a stock 350.....i changed the heads to late model vortech heads with roller rockers and went with the edelbrock intake manifold to retain the stock TBI......problem i have is the motor breaks up in higher rpms....ive changed the plugs, coil, cap and rotor. also checked the valve lashing multiple times. i have never replaced the distributor and wonder if it could be the cause of the issue??

any feedback would be great!

thanx
BBB
 
How high is high? If you are getting really high on the RPMs, you could be having "pump up" problems with the hydraulic lifters.

Check for any wobble in the dist. shaft. Worn bushings can cause problems. Also the ignition module.

You need to isolate where the problem is. Valve train, ignition, or fuel.

You might try a fuel pressure gauge that you can watch when it starts cutting out. A fuel filter or a weak pump might let you run out of gas at high speeds.
 
high as in 3200-3500rpms....the lifters are brand new hydraulics. i have a brand new fuel filter on it have never had to change the fuel pump. the dizzy does have some play. thats what was had me leaning towards a distributor problem. i just dont wanna keep throwing parts at it hoping each new part corrects it??
 
high as in 3200-3500rpms
Click to expand...

That should not be high enough for lifter problems. At this point, I am leaning toward dist. or fuel.
The chip comes in if you have changed the cam more than the computer can compensate for.
Lots of people here have done it, there are a couple of places that they use that will custom burn you a chip after you fill out an questionnaire so they know what the engine has in it.

If the dist shaft has enough side to side play to be noticeable at the top, then at best you need to start saving up for a new one or a rebuild kit.
At worst, you may need to do it soon.

I have no idea where the breakover point is as to amount.
Someone here probably has maximum allowable slop numbers, but I don't.

If you have not done so, a rebuild of your injectors along with the fuel pressure regulator would not be money wasted and might fix the problem.

And I would check the fuel pressure just for fun.
 
well with it being a throttle body it was cleaned thoroughly prior to install no seperate injectors. i too am leaning towards the distributor....i can find another nos one for about 100 bucks and may try that
 
Actually, you do have separate injectors. Two of them in fact.
My equipment is multiport, so I have never done a TBI rebuild, but lots of folks here have.
Most times it seems to help.
There are kits that include the pressure regulator that you use.

Somebody here should chime in with a link to a thread or some info on rebuilding them pretty soon.
 
It could be an ignition module, especially if it's not a Delco.. but the TBI dizzies are pretty fool-proof and when modules fail, they usually cr@p out..... it's not like your gonna have a stuck weight, the computer controls all that..


I'd be looking at fuel... do a plug reading.. and check your injector pattern... a bump in fuel pressure would probably do it a ton of good... it's not uncommon for them to have barely minimum psi #'s when they are stock.... think I bumped mine about 5 lb's, world of difference..
 
stomis i would tend to agree with you however by switching to the vortech heads which are completely bone stock, im sure i gained more airflow but at the same time this 89 has such a simplistic computer, it relys on the o2 sensors to let it know if it is running lean or rich and thats how it compensates..with the stock cam i dont think i need a chip and there's not a lot i could change parameter wise......the problem i have doesnt occur under normal driving, but it i am in some nastymud or sugar sand and need to romp on the gas pedal to power out of sumthing it would come into play
 
Your 89 will have roller lifters so hopefully that's what you replaced them with.If they were replaced with stock lifters the valve train geometry shouldn't have changed but should be checked anyway because you changed the heads.Aftermarket lifters can be different heights changing the required push rod length and also require less preload after zero lash in most cases.Also make sure you have no push rod binding in the guide holes.Don't know what you have but if you have guide plates or self aligning rockers combined with stock guide holes in the heads that will be an issue.And the dizzy does need to be replaced regardless if it has play but don't forget to backtrack and check for other issues if it doesn't resolve the problem.
 
big bearded bastard said:
stomis i would tend to agree with you however by switching to the vortech heads which are completely bone stock, im sure i gained more airflow but at the same time this 89 has such a simplistic computer, it relys on the o2 sensors to let it know if it is running lean or rich and thats how it compensates..with the stock cam i dont think i need a chip and there's not a lot i could change parameter wise......the problem i have doesnt occur under normal driving, but it i am in some nastymud or sugar sand and need to romp on the gas pedal to power out of sumthing it would come into play
Click to expand...

Then I stand by my initial statement of fuel and say its probably low pressure. Im no tuning guru but I figure that if changing the intake and exhaust characteristics via camshaft funks w/ the computer than having heads that flow different rates would also affect that same tables. :dunno:

zombie1969 said:
Your 89 will have roller lifters so hopefully that's what you replaced them with.If they were replaced with stock lifters the valve train geometry shouldn't have changed but should be checked anyway because you changed the heads.Aftermarket lifters can be different heights changing the required push rod length and also require less preload after zero lash in most cases.Also make sure you have no push rod binding in the guide holes.Don't know what you have but if you have guide plates or self aligning rockers combined with stock guide holes in the heads that will be an issue.And the dizzy does need to be replaced regardless if it has play but don't forget to backtrack and check for other issues if it doesn't resolve the problem.
Click to expand...

89 trucks did not have roller cams. They were provisioned for them but did not have them.
 
well i will change the dizzy this weekend and see what it does, i will also look into the fuel pressure. the heads and rockers as well as the lifter and new pushrods were all installed by an asme gmac etc etc mechanic....one of the best guys i know and the only one i trust. we have checked the lash a couple times since i used roller rockers and they seem to be fine.

and stomis is correct, the 89 did not have roller lifters.
 
I thought they were all roller by 89...Id kick the mec if I was you.No offence but anybody that replaces flat taps on a used cam should hang up there wrench and go home.Expect t need a new cam and lifters soon if not already.I assumed roller because every body knows you can replace the lifters on those without replacing the cam.
 
zombie1969 said:
I thought they were all roller by 89...Id kick the mec if I was you.No offence but anybody that replaces flat taps on a used cam should hang up there wrench and go home.Expect t need a new cam and lifters soon if not already.I assumed roller because every body knows you can replace the lifters on those without replacing the cam.
Click to expand...


Since when is it a no no to put new lifters on an old cam? Its mixing up the used lifters and reusing them that wipes lobes.
 
ive never had a problem replacing just the lifters and not the cam. not saying that you arent correct but the last motor i did it to got an add'l 150k before it finally slung a main bearing
 
zombie1969 said:
I thought they were all roller by 89...Id kick the mec if I was you.No offence but anybody that replaces flat taps on a used cam should hang up there wrench and go home.Expect t need a new cam and lifters soon if not already.I assumed roller because every body knows you can replace the lifters on those without replacing the cam.
Click to expand...

The TBI TRUCK engines from 1987-1995 were ALL flat tappet hydraulic cams, the roller cam was not used in trucks until the vortec engine came out in 1996 but most of the 87-95 blocks were provisioned for a roller cam. Cars got roller cams starting in 1987.

It is ok to install new lifters on an old cam but NEVER used lifter on a new cam or using old lifters over that have not been kept in order to go back on the same lobe they came off of.
 
You must log in or register to reply here.

Latest Posts

Top Bottom