Jeep Strokers

I’m about 7K miles into the 4.7L I built last summer with Russ’ help and guidance. It’s been driving great with zero issues until recently and even then, it’s inconsistent. About 2 months ago I developed a problem with it starting while hot. It only happens after I’ve driven it a bit, like to the store or gas station, but also occurs after longer trips like to work (39mi). I took it to my local shop and just from listening to it he thought it might be an injector failing to close all the way and leaking fuel into the combustion chamber after it’s shut off.

I just put a fuel pressure gauge on the fuel rail to see if pressure dropped after running it and shutting it off. That should indicate a leak, right? Anyway, pressure seems to remain constant when off but it still stumbles and clunks upon starting it. It’ll start in that condition but sounds completely different and when I open the throttle it sounds horrible; clearly something wrong. I’ll shut it off and try it over and over again until it starts correctly then it drives like normal.

If you guys can review the attached videos and gimme some suggestions I’d greatly appreciate the help. In the 2nd video, starting it while hot, it exhibits the problem start first. Then I shut it off and immediately restart it and it runs normally. This is typically what I have to do when making a stop on the way home or when running errands. Pain in the a$$.

Normal Jeep start from cold.
https://youtube.com/shorts/6m1vcSCaTXE?feature=share

Malfunction Jeep start from hot.
https://youtu.be/cCFR7WUmVuA

What size pump in LPH?
and what size Injectors in cc/min or #/HR?
Also, what octane fuel?

You're running a return line back to the tank right?

The fuel pump is a standard OEM pump in the gas tank.

Injectors are Bosch 24lb/hr.

Fuel is 87 octane pump gas.

Fuel return line was disconnected only from the fuel rail when I pulled the engine. It’s been plugged back in since reinstalling.

Btw, this is a 94 YJ I’m talking about.

Your engine is starving man. Leaving so much power on the table. The stock YJ fuel pump is only a 150-170 LPH unit and the regulator limits pressure to 30-38 PSI. 24#/HR injectors for a 4.7L are wildly insufficient. The max HP you could achieve with your current fuel system is 215 Crankshaft HP @ 90% duty cycle. That's basically a stock 4.0L engine. Get some 35#/HR injectors and a 255 LPH pump. Replace the regulator and monitor the fuel pressure. Fuel pressure should jump up a bit with the stronger pump.




https://www.racetronix.biz/p/255l-hr-fuel-pump/gss315

https://www.racetronix.biz/p/255l-hr-fu ... ume/rxp252

The stock 90lph fuel pump is good for up to 300 crank HP, and your injector size is appropriate, so I don't see any problems there.
It does appear that you're getting vapor lock inside the injector rail due to heat soaking from the exhaust manifold. You could try attaching a heat shield to the underside of the intake manifold and see if that remedies the problem.

https://www.angelfire.com/my/fan/manifold.html

Cheromaniac wrote: ↑May 16th, 2022, 1:15 am The stock 90lph fuel pump is good for up to 300 crank HP, and your injector size is appropriate, so I don't see any problems there.
It does appear that you're getting vapor lock inside the injector rail due to heat soaking from the exhaust manifold. You could try attaching a heat shield to the underside of the intake manifold and see if that remedies the problem.

https://www.angelfire.com/my/fan/manifold.html

I’ve got the DEI heat shield package mostly installed: manifold shield and fuel rail wrap. The individual injector wraps are currently off because I thought I may have to pull the injectors.

I don’t know if it’s audible in the video but there’s a distinct clunk when this happens as soon as I turn the key. The engine will typically turn over a couple times then I get that clunk then it starts and runs like it’s missing 2 cylinders. I think that’s why the local mechanic thought it was fuel leaking into the chamber; like it’s fluid that isn’t compressing. With that in mind I pulled the dipstick to smell for gas: nothing. I even put a lighter to it to see if anything ignited, still nothing.

Other than this, the thing is running like a champ. Eating a lot of gas but running very smoothly. Frustrating.

In the last week I’ve accomplished the following:

Added adhesive thermal barrier to the underside of the intake manifold and both fuel and return lines.

Installed an AFR gauge: 14.6-15.0 from idle to 3K, runs a little lean for a while on a bad start then levels out.

Pulled the spark plugs after letting idle for 30min: clean, dry, slightly white on the electrode.

Replaced a cracked vacuum hose connector that led from the manifold to the MAP sensor.

No change in how it starts hot. In fact, when it starts like this and I let it idle the ratio still reads optimal: 14.7.

Pac8541 wrote: ↑May 30th, 2022, 12:37 pm
Installed an AFR gauge: 14.6-15.0 from idle to 3K, runs a little lean for a while on a bad start then levels out.

A Narrowband O2 gauge will tell you next to nothing. The narrowband O2 voltage spectrum is only 0-1 volt so they can only produce a reading that ranges from 14:1 to 15:1. Meanwhile the actual ratio could be anywhere between 10:1 to 18:1. The 15:1 reading you got during the poor start could very well be 18:1. I would replace the fuel pump with a 255 Walbro or at least a 190.

You might want to test the existing stock fuel pump and see if its output is within spec before you replace it. If you haven't recently replaced the fuel filter, now would be a good time to do it.

The AFR gauge is a wideband Autometer. The fuel pump has not been addressed yet and the fuel filter is 6 months since last replaced.

It’s headed to a professional tomorrow morning; I’ve done everything I have time to. When the cause is determined, I’ll let you know. Thank you for your input.

This may be too little, too late, but for what it's worth. This sounds like more of an intermittent electrical issue than fueling to me. A serious lean condition wouldn't just come and go, and would be worse when cold, not hot. Hopefully the professional you took it to can resolve it quick and assuredly for you. In case they have it for a while and can't figure things out, couple things I'd verify 1st: Distributor sync will cause firing & injector issues on OBD1. Mine wouldn't accept throttle, much like in yours vidi when it was out of phase, or just pushed beyond limits it's capable of adjusting for, maybe due to heat soak or other factors. The injectors won't fire in-time if thats out of range, or maybe not even fire at all. They block-fire on obd1's so this would give the impression of multiple cylinders missing when this happens. Even tho the ignition will still fire normally.
Older wiring harnesses can haunt you with bad connections (dirty or corroded), and this causes the resistance in the circuits to go up inconsistently, and Way up w/ heat soak. This changes the voltages that the ECU see's for any affected sensors and then throws off the calibration. I've had to deal with this on my '92 over the last ~20yrs Same story for bad ground connections. Check all your connections again and clean all your ground points. Even better, buy a couple extra universal ground wires from your local parts store and just double everywhere that one already exists. Double check your crank position sensor wire is clear of the exhaust on #6.
Lastly, the multi-pin connector at the ECU is terrible for bad contacts as these jeeps age. They aren't weather proofed, so if you're doing any kind of serious wheeing ir water crossing, they can get pretty bad. **Disconnect your battery before messing with this connector** You don't necessarily have to remove it all the way, just back out the little 8mm bolt a handful of turns and gently wiggle the plug back. You can see at the junction of it and the ECU if you're making any progress. Then just lightly snug the bolt back down and reconnect the batt. This has remedied a few random issues for me before. Good luck, hope you can get it back running reliably soon!

Dropped off the Jeep at a recommended shop yesterday and the photos are what they found. This was a brand new distributor installed and attached to a new camshaft and HV oil pump, 6 months ago. The accelerated wear on the distro gear teeth and the bent tab thing wedged between 2 teeth explains every symptom I was seeing other than the fact that the problem rarely surfaced on anything but a hot start. Recently however, it WAS occurring on a cold start. According to the mechanic that replaced the distributor, there isn’t any obvious wear on the camshaft gear but I’ll confirm that later when I replace the oil pump.

Speaking of which, I thought I read somewhere that the HV oil pumps can be hard on this exact part, the distributor gear. Whose experienced this and why does it happen? It would be easy for me to draw that conclusion at this point but correlation does not always mean causation so I’m looking for others’ insight. I’ve also spoken to brother Russ about all this several times in the past couple weeks as well as the machinist turned close friend who did all the block work. They’ve both been extremely helpful but ultimately it’s come down to something no one had thought of.

Jeep is back in my driveway running perfectly. I’ll be keeping a close eye on this in the coming months.

Ps: Torquesplit, thank you for all that info. I just now saw your post as I was previewing this one. Great insight and in a roundabout way, you nailed the problem.

Actually, the more I examine the gear teeth the more I see that they’re all worn evenly. The photo makes it look like some teeth are worn a lot more than the rest. It’s just the lighting in the photo. The does appear to be more wear than I’d expect since there’s a shoulder cut into each tooth from where the cam gear was engaging them but I believe the cause of why it was starting poorly is that tab bent out of position and mashed between 2 teeth.

Glad you got it back so quickly and it's running good Happy to try & help. interesting pics you have there! I'm very curious how that thrust washer tab got bent down? Could speculate for hours but ultimately you have a new one now and hopefully no more worries about it. That gear is pretty gnarly for only 7k miles. Maybe fighting itself with that bent tab caused some increased wear. Amazing it didn't jump time on the dizzy! Just keep an eye on the new one and see how it's holding up. Plenty of conflicting opinions about HV oil pumps out there, so i won't even go there right now. For now I'd just be curious what oil you're running, and what cold & hot oil pressures your seeing with it? We can talk about plenty on here, but probably best to stay with Russ and your machinist's recommendations for now, since they know your whole setup.

Torqsplit wrote: ↑June 2nd, 2022, 7:04 pm Glad you got it back so quickly and it's running good Happy to try & help. interesting pics you have there! I'm very curious how that thrust washer tab got bent down? Could speculate for hours but ultimately you have a new one now and hopefully no more worries about it. That gear is pretty gnarly for only 7k miles. Maybe fighting itself with that bent tab caused some increased wear. Amazing it didn't jump time on the dizzy! Just keep an eye on the new one and see how it's holding up. Plenty of conflicting opinions about HV oil pumps out there, so i won't even go there right now. For now I'd just be curious what oil you're running, and what cold & hot oil pressures your seeing with it? We can talk about plenty on here, but probably best to stay with Russ and your machinist's recommendations for now, since they know your whole setup.

I’ve been running nothing but Driven oil since day 1: BR30 initially then HR2 10W30. It’s on its 3rd oil change after break in now so, 5th overall. Pressure at start up and after warming stays constant at 42.

I’m gonna go to an auto parts store tomorrow and inspect a brand new distributor. I’m curious if there’s a step in each tooth like that by design. I don’t believe there is but I never looked specifically. I don’t know why there would be. There are clearly metal shavings coming off the teeth and I find that concerning.

Camshaft is one of Russ’ custom grind and nitride coated Comp Cams sticks, btw.