Hesitation under load after rebuild

doctorj357

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Aug 7, 2018
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Recently did a top end rebuild on my 95 GTS. Car has been sitting since Sept last year and started my project back in Mar/Apr.

Most everything bolted on top of the block is brand new. New rubber galore, new gaskets everywhere. Car is pretty much stock but am sporting Edelbrock Performer '60329' heads that originally came with the car. I also had them cleaned and resurfaced. I ditched my E-303 and added a nib Melling SYB-51 cam, along with their pushrods and lifters. The distributor is a new Cardone (not remanfactured) and also replaced the TIF sensor last year. In order to use the stock intake with Fox valve covers, I added a .5in phenolic spacer which prevented the EGR tube from reaching. ch so I bought some 5/8 brass compression sleeves at the local HW store and maguivered them onto both ends of the egr tube and tightened down. Its a perfect fit and does not appear to be leaking.

First startup - car runs fine. Ran it for about 40min at various rpms to break in the came. I can tell there is at least one rocker slightly out of adjustment 'ticking' but hasn't gotten worse yet. Next day, changed the oil and fired it up. It starts up and idles perfectly. Base timing was set to 10deg btdc. Also am currently running the Autolite 3924 plugs. So far have put about 20mi on it with zero issues, until today, 2 days later I started experiencing a stuttering effect when under load. Seems to be more prevalent under 3500rpm.

Things I have done
Pulled codes. Nothing. Just 111 'System Pass'
Checked for loose distributor, wires, nothing.
Checked MAF, nice a clean in factory air box
Checked EGR and holds when under vacuum

Things i have not done yet
Cylinder Balance Test
Fuel Pressure Test
Spark Plug gap ( i honestly don't remember what I set them too last year. I think .054)

I was planing having a shop look it for the rocker adjustment, but I might have them look at this too. Does not apear to prevent me from driving the car, but before i drive it any further, just curious what others have experienced after a rebuild or parts replacement that could be contributing?
 
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1989FoxBro

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I rebuilt mine a few years ago and it would backfire under heavy load. I figured out that one of my injectors was unplugged underneath my intake plenum where I couldn't really see it. Sometimes it's that easy but like you said, you checked your wires so I imagine it's not that.

So stuttering as in like the RPM's stutter or it backfires or just doesn't really accelerate at that load? Does it happen at all speeds and all gears at around the same RPM?
 

jozsefsz

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Did the weather change a lot from hot to cool or visa versa? That's enough to muck with driveability. It could also be that your computer leaned things out as it learned 'proper' fueling and the stock tune now isn't as compatible with the cam is it previously was. You could try resetting the computer (disconnect battery for a while) and see if it runs properly again. If it does, a tune may help.
 

doctorj357

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I rebuilt mine a few years ago and it would backfire under heavy load. I figured out that one of my injectors was unplugged underneath my intake plenum where I couldn't really see it. Sometimes it's that easy but like you said, you checked your wires so I imagine it's not that.


So stuttering as in like the RPM's stutter or it backfires or just doesn't really accelerate at that load? Does it happen at all speeds and all gears at around the same RPM?


Its not pinging, and I don't believe its detonation. Stuttering almost like its running out of fuel, but only when under load. If I take my foot of the gas it stays running fine.



Did the weather change a lot from hot to cool or visa versa? That's enough to muck with driveability. It could also be that your computer leaned things out as it learned 'proper' fueling and the stock tune now isn't as compatible with the cam is it previously was. You could try resetting the computer (disconnect battery for a while) and see if it runs properly again. If it does, a tune may help.

No, weather here in MI was steady 80F+. Issue only revealed itself after the engine was hot and driving for 15min or more around town. The cam in there now is a OEM replacement and supposedly has a stock profile. But I was thikning this, about resetting the computer just as a precaution as it may have learned a A/F table incorrectly.
 
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doctorj357

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It still starts and idles fine (for now), but I'm going to have to drive it more today to try and get a feel for what's going on. Maybe drive up to autozone and rent a fuel pressure gauge and see if it drops when driving.
 
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doctorj357

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Anythings possible at this point. I pulled the passenger side vc and readjusted the rockers again. will see if that made any difference in the ticking. But while I had the upper intake removed, decided to check the lower intake bolts.

Initially I torqued them down to 17ftlbs during installation. Took me about dozen cycles before all bolts properly torqued. But I forgot to set final torque to 25ftlbs + forgot to check it after a few warm ups. Good thing I checked......................So went through the torque sequence again at 17ftlbs, which a few needed it. Followed by the final sequence at 25ftlbs, which also took two cycles to set.

Probably totally unrelated to my issue, but that potentially could have just lead to something else. Going to road test again later tonight
 

jozsefsz

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I'm leaning towards your learned-fuel-trims issue as well. The "after it warms up and you drive it for a while" indicates that it's switched from open-loop to closed-loop and the learned fuel-trims take over. If you see that happening with significant hesitation / bucking, it's making things over-lean. Let us know how the road-test goes.
 

doctorj357

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Roadtest was suspended. In my efforts to adjust the Rockers yesterday, one of my valve cover bolts rounded off. Which I don't get, I only torqued to 10ft lbs. But the head was really lodged. I had to use a angle grinder to cut the head off, marred up my vc in the process. But got the bolt out today, but then hardware closed at 5pm. So won't be until tomorrow night sometime.

In meantime, not sure if relevant but I am using a set of EV6 injectors (Bosch 19lb - F6VE-A5A). I got them NOS for $20. I've read good/bad about these on other forums. Making me wonder if in the fuel tables isn't jiving with injector pulses. Couldn't hurt to swap back in the stock EV1 injectors.
 

jozsefsz

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I've had terrible luck with the Bosch injectors. I went through a couple sets of 'tested' green giant 42lb injectors before throwing them in the trash. Now these were ebay specials so not exactly NOS, but I could not get the car to run properly with them. Really inconsistent, very hard to tune, and then ultimately stuck open. A cylinder balance test can help you determine if one or more is out-of-whack. The computer is capable of learning fueling (based on o2 sensor output) for a reasonable range (I think 10% adjustment un-tuned iirc?) and if it tries to go outside that range it'll throw a code.

One thing to note is that Ford flow-rates are determined at 39psi and a lot of aftermarket injectors are rated at 43.5psi. So... if your 19lb. bosch was rated at 43.5psi and your 19lb. Ford were rated at 39psi, and your fuel-pressure regulator is pushing 39psi (stock), then your new 19's are actually behaving like 18's (https://www.deatschwerks.com/fuel-calculators/flow-vs-pressure-calculator). This could cause you to run lean enough to cause stumbling and bucking for sure.
An adjustable fuel-pressure regulator and dialing up your fuel-pressure to 43.5 (where the injectors were rated) could help solve this.
 

doctorj357

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So new development - Took it out for a ride today, but was cut short as I got oil blowing out somewhere, BAD..... getting all over the h-pipe and smoking like hell.

Over the past couple days, I readjusted the rockers. While I was doing this, I decided to change out the valve covers to a set of Ford Motorsports. They were in immaculate condition and the baffles were already hammered out to work with 1.6rr. For $60 figured I couldn't go wrong. So I changed out my Fox vc's for these today.

I immediately noticed that the oil fill holes were in the wrong location now. Before on the Fox vc's I had a oil filler neck with a 90deg port to connect a line to the intake. Now with these new vc's I have nothing. Just a hole in each. So the drivers side I put in a twist style oil cap and fits (just barely) underneath the upper intake when bolted down. As for the passenger side, I had to somehow reattach the rubber line from the intake back onto the valve cover. But since no oil filler neck with a 90deg port like before, I improvised. I put a rubber grommet into that vc and added a PCV valve. Then connected the line. Problem solved............ or so I thought


During a test drive all a sudden smoke started billow out of the car, under the hood. At first I thought "great" the new valve covers weren't sealing and spewing oil all over the manifolds. As I looked underneath, appears to be further back, towards the transmission. I'm wondering if by changing to that PCV in the valve cover, I somehow changed how the crankcase pressure and caused a rear main to blow out. Its certainly in the right location where the drip is, but is only leaking when the engine is running

Oh, other than that, fixed my chattering rockers and now it sounds great, minus the whole oil burning thing. But regarding the injectors, I just might put the stock ones back on. They tested fine. I just thought I might be getting a better injector out of the Bosch ones. But sounds like popular opinion is they have/had issues.
 

7991LXnSHO

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Please do not skip the tests/ steps not done once you have the OEM injectors in.
It would be easy to have a vac. leak after doing the top end work. The Fox upper intake has a big, capped vac. line that is easy to forget about since nothing gets attached and it’s out of sight. Even a cracked line could be causing an issue if you have not updated them.

Recently did a top end rebuild on my 95 GTS. Car has been sitting since Sept last year and started my project back in Mar/Apr.

Most everything bolted on top of the block is brand new. New rubber galore, new gaskets everywhere. Car is pretty much stock but am sporting Edelbrock Performer '60329' heads that originally came with the car. I also had them cleaned and resurfaced. I ditched my E-303 and added a nib Melling SYB-51 cam, along with their pushrods and lifters. The distributor is a new Cardone (not remanfactured) and also replaced the TIF sensor last year. In order to use the stock intake with Fox valve covers, I added a .5in phenolic spacer which prevented the EGR tube from reaching. ch so I bought some 5/8 brass compression sleeves at the local HW store and maguivered them onto both ends of the egr tube and tightened down. Its a perfect fit and does not appear to be leaking.

First startup - car runs fine. Ran it for about 40min at various rpms to break in the came. I can tell there is at least one rocker slightly out of adjustment 'ticking' but hasn't gotten worse yet. Next day, changed the oil and fired it up. It starts up and idles perfectly. Base timing was set to 10deg btdc. Also am currently running the Autolite 3924 plugs. So far have put about 20mi on it with zero issues, until today, 2 days later I started experiencing a stuttering effect when under load. Seems to be more prevalent under 3500rpm.

Things I have done
Pulled codes. Nothing. Just 111 'System Pass'
Checked for loose distributor, wires, nothing.
Checked MAF, nice a clean in factory air box
Checked EGR and holds when under vacuum

Things i have not done yet
Cylinder Balance Test
Fuel Pressure Test
Spark Plug gap ( i honestly don't remember what I set them too last year. I think .054)

I was planing having a shop look it for the rocker adjustment, but I might have them look at this too. Does not apear to prevent me from driving the car, but before i drive it any further, just curious what others have experienced after a rebuild or parts replacement that could be contributing?
 
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doctorj357

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So turned out was not a main oil seal that was blown. Someone, not going to name names, but 'someone' used the wrong bolts for the valve covers and wasn't making a decent seal. SOMEONE lol


But as for the hesitation. As it been suggested, those Bosch ones may be rated for a higher psi and if I'm at stock, may cause a lean condition which could cause that hesitation/bucking. So while I was fixing my newly discovered leaky valve covers, I decided to switch out the Bosch 19lb injectors and go back to the stock 19lb injectors.

I drove the car for about 45min non stop with no observed issues. Appears no more hesitation
 
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