New Stroker stumbling at WOT

[go4lo]

I've got about 850 miles on my 4.7L stroker and it's started to stumble at WOT under load. It idles very smooth and and runs great until it's pushed to 3K or more RPMs. In park under no load it will rev up to red line but under load at 3K it's like it hits a wall. I did the proper break in with Comp Cams Break In oil, changed the oil and filter have been running a second round of Comp Cams Break In oil. Some have said that the Hi-Zinc oils can clog a CAT, could my new Magnaflow CAT be clogged already?

Where do you guys suggest I start?

[domster]

Mate I'm no expert being on my first stroker myself, but I'd check the following:

WOT under load would likely be peak fuel demand for your stroker. That would be the first place I'd look.

-What size injectors are you using?
-OBD1 / OBD2 fuel setup - what pressure are you running on the fuel rail a) at idle, full vac and b) with vac disconnected?
-fuel pump setup and capacity?

Then go spark - high demand on your ignition system too at WOT

- New or old coil?
- Fresh leads / plugs?
- Is dizzy set up (indexed) correctly to allow full advance? No, you can't change timing but the rotor tip needs to be positioned correctly to receive the spark all the way up the advance curve.

How's the intake air looking? Large TB? FIPK? You're not choking it somewhere?


Last but not least, I made the mistake of not properly seating the connector on my generator when I ran my stroker in. This meant the batt wasn't charging and I couldn't rev it over 3k without misfiring due to low batt volts. Not saying you've done that, but is the PCM getting a good supply of juice?

Just some ideas, but as stated I'm a newbie too.....with a problem at the other end of the scale!

[SilverXJ]

I'm thinking fuel flow or injectors as well.

If your cat was new, then its not the cat. High Zinc oils can clog the cat, but that takes time.

You can also check the TPS and reindex the distributor.

[go4lo]

Sorry I should have included more info:

OBD II System - '99 XJ
Stock Fuel Pump from '99 XJ
93 Octane Fuel
Bosch EV6 24lb Blue Injectors
New Accell - Coil, Cap, Rotor, 8mm wires, Plugs set to .040 Gap
63mm Bored TB
AEM Brute Force Intake
Passetter header to Carsound/MF Cat to FM 40 series to turn down.
DIY P&P 0630 Head

I don't see where a "choke" down in the system could be other than a clogged cat. Why would the engine rev fine under no load and stumble under load? What am I missing?

[stege123]

Are you using the stock valve springs ?. sounds like valve float

[4.whoa]

What is it doing? Sputtering,missing out ,like that? does it stop if you lift up a little? or is it any amount of a load?

[go4lo]

Are you using the stock valve springs ?. sounds like valve float

Mopar Perf valve springs #5249464
retainers #4452032 (8*) 8mm
locks #4529218 (8*) 8mm
New single lock Sealed Power valves and 3 angle valve job
Harland Sharp Roller Rockers

What is it doing? Sputtering,missing out ,like that? does it stop if you lift up a little? or is it any amount of a load?

Once you hit 3K it acts like it's not getting any more fuel. If I back off everythings fine, no stalling. It's like someone put a rev limiter on it at 3K while under load. It will typically only do this in 3rd gear. I can sometimes keep pressing the pedal down and power through it but it's still not full power. Possible transmission related?

[dwg86]

Make sure your cam position sensor (where distributor used to be) is indexed correctly. You might have to take it to a dealer. They will use a DRB to sync the CPS. It only takes about 10 mins.

[go4lo]

Make sure your cam position sensor (where distributor used to be) is indexed correctly. You might have to take it to a dealer. They will use a DRB to sync the CPS. It only takes about 10 mins.

I thought about this too, but wouldn't this have show up in the first 800 miles? Could the CPS become "unindexed"? FYI - I still have a distributor on my engine, no coil packs.

[6TIME]

I had a similar symptoms a while back and the distributor was indexed a tooth off. The computer seems to be able to compensate surprisingly well for the the dizzy being clocked wrong at lower rpms, the upper rpm range is where the problem became evident. Confirm that your distributor is indexed properly!

[SilverXJ]

As I said earlier I would re index the distributor.

However, I think it is a fuel issue. Try to put a gauge on it while you are driving. My mom's WJ had a wall at about 3500 rpm. No backfiring, sputtering or anything. The fuel pump was bad. It would check fine at idle but when you hit 3500 the fuel pressure would drop.

[go4lo]

Sorry for bringing this post back up from the bottom but I'm still having the WOT hesitation/stall problems. I finally have some time this week to work on it so today I pulled the dizzy to re-index and followed the correct procedure per the FSM and Dino's instructions:

Set no.1 cyclinder to Top Dead Center
Verified it was the compression stroke, NOT exhaust
Put a tooth pick in the dizzy
Set the oil pump slot to 11/5
Drop the dizzy in with ears pointing at 1
Rotate into place, Rotor pointing at 5

Dizzy settles in nicely but the ears aren't lined up with the threaded hole in the block for the hold down. At this point I'm forced to rotate the crankshaft clockwise a few more degrees to line the ears up so the bolt will tighten down. This causes the rotor to be at 5:30ish and past the no.1 plug. I keep reading other threads where people have been have the same hesitation/stalling problems and the fix seems to always be re-indexing the distributor by a tooth.

I'm confused about moving the dizzy by a "tooth". I tried to rotate it counter clockwise by a tooth but the ears on the dizzy hold down hit the block when I try to drop the dizzy in with them pointed any earlier than 1, ie 12 or 11. Any ideas? Do I need to grind down the ears so I can rotate it further? For reference I'm running a Comp Cams 68-231-4 cam. Anyone else out there with aftermarket cams have any problems indexing the dizzy?

[Bodo]

You will have to cut your ears off of the dizzy. Sounds like you indexed and installed it correctly when the tabs don't line up with the hole. When I did mine, the ear just blocked the bolt hole.

Cut the tabs off, then re-do it using the method you described and let it roll.

[go4lo]

Ok so tonight I decided to start from the beginning once more to make sure I hadn't missed anything.

Pulled the number 1 plug.
Finger over the hole until compression stroke is felt
Continue to rotate crankshaft until mark on balancer is set to 0 on timing cover
Set oil pump slot to 11/5 o'clock
Put drift pin in dizzy to hold location (used a torx wrench)
Start dizzy at 1 o'clock and rotate into place

First try this is what I end up with, rotor is in perfect spot but the ear of the dizzy is covering half of the hole.





Second step, pull dizzy back out file the ear down that's in the way, reinstall and tighten bolt down



Pull drift pin out, both holes are lined up perfectly, check and double check everything else.
Jeep fires right up and idles as smooth as ever. Take if or a spin around the block and PROBLEM IS STILL THERE!!

The truck acts like the fuel supply is instantly cut off when get on it off the line. The RPMs won't go over 3K then they drop back and it recovers.

At this point I'm back to the two basics, SPARK and FUEL. I'm confident the motor is getting spark and I'm leaning towards fuel delivery being the problem. I wanted to rule out the obvious before spending $200 on a fuel pump. BUT the pump that's feeding my stroker is the stock pump that was probably never changed before I got it and has 174,000 miles on it.

I did put a new pick up screen on it during my build and cleaned the tank so I don't feel like it's dirty. I think the stroker has just put it over the edge....at least I hope that is it. What do you guys think? I plan to pick up a pump kit tomorrow so my fingers are crossed.

[yuppiexj]

Like he said cut the ears off, missed the earlier post