Runs like crap on hot start.

Hey Everyone, I have had this problem for awhile but it’s been getting worse.

Daily driving its fine and this never happens. It’s only on trail runs that it seems to give me a problem. After wheeling for awhile with lots of idle time and high under hood temps it doesn't run right on startup. Turn the jeep off and restart a few minutes later and it idles very rough and is down a cylinder or two. A few revs or idling for long enough and it clears up. It doesn't smoke backfire or anything. It starts right up like normal but runs very rough.

This weekend it seemed to be worse. I had to back down a steep trail to recover a friend. While sitting in the vehicle while they got it hooked up it was idling fine. When I went to make the pull it was down a cylinder or two. I brought the revs up to about 3K and held it for a bit and it cleared right up and was able to pull. It’s unlikely this could be unrelated but it might have had something to do with the angle, hell I had to slouch down in my seat to use the headrest as my neck was tired from holding it up. Under hood temps were once again high as I was working the crap out of it and then idling between pulls.

Any ideas? Vehicle specs are 97 Cherokee with 4.6L Stroker with about 30K miles on it, Ford 24lb injectors, recent cap and rotor, brand new Taylor wires.

I was thinking a slim chance of vapor lock which could be made worse by the 97+ not having a return off the rail. But at 45psi of fuel pressure I would think it would be harder to boil the fuel? I do have two spare injectors I could swap in and out to see if it cleared up at all. Thanks for any help!

EDIT: No codes or check engine lamp during any of this.

Clark

happened to my last jeep, and my current one. I have yet to find a solution, although i dont have a stroker either.

you could try some lebaron hood vents, try to get the hot air out of the engine bay faster...

The 90 I just bought does the same thing. I am replacing all the basic maintanance stuff to see if it cures it and I plan on venting the hood, too.
Maybe wrap the fuel line to the engine with a heat shield?

On the 00-01 there is a TSB for hot and cold start issues. The hot has you put a heat shield over the #3 injector. This might help JeepAddict.

BlueCuda, what intake manifold are you running? And do you know which cylinder is having the misfire?

Do a search for "heat soak", lots of threads on this.

^ X2....your boiling your fuel and injecting your gasoline as a gas into the combustion chamber. Look into a heat shield or vents or both.

x3 sounds like heat soak.

A e-fan manual switch is reported to help keep things cooler under the hood. Don't know if yours was on in this case, but after turning motor off and restarting, this can help.

winterbeater said:

A e-fan manual switch is reported to help keep things cooler under the hood. Don't know if yours was on in this case, but after turning motor off and restarting, this can help.

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x2 on Winterbeater's post. You can even buy an electronic delay module that allows you to run the efan for a user selectable period after shutdown:

http://www.at-fairfax.com/ConstructionElectronics/RelayBoardDelayTimers.htm

The ELK-960 at the bottom of the page would be my choice, it can be set for seconds or minutes of duration.

I am not a big fan of the ford injectors, my stroker had the same problems, so I found some stock grey top injectors that supposedly have a higher flow rate and my problem was solved. One thing I have also noticed with the Ford injectors on my Renix setup was that the injector body is longer than the stock units and would contact the intake manifold injector bores and make it easier to transfer heat into the fuel system. I tried notching the injector rail bolt holes so that the injectors were moved farther from the intake manifold, but it didn't help my situation. Sorry for the long post but I just never seen anyone mention this before.

IH392 said:

I am not a big fan of the ford injectors, my stroker had the same problems, so I found some stock grey top injectors that supposedly have a higher flow rate and my problem was solved. One thing I have also noticed with the Ford injectors on my Renix setup was that the injector body is longer than the stock units and would contact the intake manifold injector bores and make it easier to transfer heat into the fuel system. I tried notching the injector rail bolt holes so that the injectors were moved farther from the intake manifold, but it didn't help my situation. Sorry for the long post but I just never seen anyone mention this before.

Click to expand...

Just seeking knowledge here.

The guys I know running strokers with the 24lb Ford injectors have used adjustable MAP sensors. Do you have to run one with your injectors? And, instead of elongating the fuel rail mounting holes, wouldn't you have been better off to use washers to raise the rail? Thanks.

I am not running any kind of adjustable map, runs great never had a code of any kind.

I am running the stock 97 intake.

This combo has been running for almost 5 years now with no trouble. Maybe it's an injector getting weak and the heat soak is making It act up? I have wheeled this thing all day in 100* heat with the AC on and not had this happen. That bieng said I am sure some hood vents would not do any harm.

Thanks for all the replies!

Before you cut the hood, try using stacks of washers to raise the rear of the hood to increase airflow. Unless you like the look of louvers, of course.

I don't know if you will get enough heat off the injectors and fuel rail with louvers or raising the rear of the hood. I don't know why Jeep saw fit to ignore this problem when a simple fix would have been a timer circuit for the efan, hell, that is standard on a lot of vehicles.

BlueCuda said:

I am not running any kind of adjustable map, runs great never had a code of any kind.

I am running the stock 97 intake.

This combo has been running for almost 5 years now with no trouble. Maybe it's an injector getting weak and the heat soak is making It act up? I have wheeled this thing all day in 100* heat with the AC on and not had this happen. That bieng said I am sure some hood vents would not do any harm.

Thanks for all the replies!

Click to expand...

Mine started acting up after about 10 years. I posted here and was advised about the tsb listed in another post.
I insulated the #3 and #4 injectors. That cleared it up immediately and, so far, permanently.
Mine is a 97, and the injectors are shaped differently than the models covered in the tsb. I had to do some rigging to get the injectors properly insulated, but it definitely worked. I used the insulator sleeves from the tsb. Got them from Chrysler for about $5 each. I used about 1 and 1/2 sleeves to insulate the two injectors. I used 4 small pieces (2 on top of the injector and 2 under it) along with a couple zip ties to do the trick.

joe_peters said:

You can even buy an electronic delay module that allows you to run the efan for a user selectable period after shutdown:
http://www.at-fairfax.com/ConstructionElectronics/RelayBoardDelayTimers.htm
The ELK-960 at the bottom of the page would be my choice, it can be set for seconds or minutes of duration.

Click to expand...

After trying the various fixes for the hot soak problem in my 01 XJ without success, a year ago I added the above timer.
When stopping on hot days or after a long uphill grind, I push the timer's power button. The timer is set to run the electric fan 2-3 minutes, enough to blow some of the exhaust heat out of the engine bay and to keep the vapor lock from occurring.
The 2001 XJs have the added heat source of two mini-cats, attached to the exhaust manifolds.
As said before, too bad the Factory didn't do this. They could have been done it simply with software. The ECM has the needed temperature sensors and already controls the e-fans relay.

Photos of timer.
http://www.flickr.com/photos/lwade/sets/72157617434915718/

lazyxj said:

After trying the various fixes for the hot soak problem in my 01 XJ without success

Click to expand...

Even the injector heat shield didn't help?

The 2001 XJs have the added heat source of two mini-cats, attached to the exhaust manifolds.

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Its actually the Cali emissions package that adds the two cats, not the MY 2001 as it came on 2000s as well.

Talyn said:

Even the injector heat shield didn't help?

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Well, they helped some but did not stop it on hot summer days or after long, hard, slow climbs.
100+ degree days are common here for several months.
The mini-cats dump a lot of heat just under the intake and fuel rail
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The timer is a PIA but it does put a stop to it.

You could wire that timer in so that it runs the fan for the selected time every time you shut off the engine, that way you can't forget to do it.

joe_peters said:

You could wire that timer in so that it runs the fan for the selected time every time you shut off the engine, that way you can't forget to do it.

Click to expand...

It's only needed in hot weather or after hard slow climbs.
An adjustable temperature switch might be a better way to activate the timer but the button works fine.

How would you wire it so it would turn on every time the engine is turned off without adding more relays? It's has enough complexity as is.

Preferably, finding a cure to the problem would be the best solution.

i am having this problem on a 90 inline 6, should i put the fan switch in and try to shield the injectors.