Ford 5.0 injectors(RENIX) hot start issue.

[xjtrailrider]

Like the title says, it starts fine cold runs like a champ weather hot or cold but if I shut it down hot it will not start until it has cooled for at least 20min. I did not have this issue with the OEM replacement injectors that were in there.

I'm assuming the issue is hot soak but why didn't it do this with the stock injectors?

 

[joe_peters]

Doubt heat soak on a Renix.

First, heat soak is not a no-start issue, rather it is a rough running issue usually on a hot restart and it will clear after a short time as you drive.

More likely early stages thermal failure CPS/CKP crank sensor.

Heat soak presents in the later--99-01 XJs with the 4.0 due to a number of design changes, the following all IMHO causes:

The root of the issue seems to be the elimination in 97 of the fuel return line off the fuel pressure regulator on the fuel rail. Follow that by the 99+ redesign on the manifolds, and I believe the adoption of the newer style "stick" injectors had their part to play (although there is a claim that they are less susceptible to heat). Some blame the insane 50 state emission package with the mini-CATs, but heat soak also presents frequently in the 49 state package XJs.

Next time it won't start, measure your resistance at the CPS/CKP--should be in the 125~275 ohm range for the Renix.

 

[96XJ_4.0]

Vapor lock?

You boiling the fuel before it gets to the injectors?

 

[xjtrailrider]

Doubt heat soak on a Renix.

First, heat soak is not a no-start issue, rather it is a rough running issue usually on a hot restart and it will clear after a short time as you drive.

It will start after a lot of cranking and runs real rough if at all, but will eventually clear out. That's what got me thinking it was heat soak.

More likely early stages thermal failure CPS/CKP crank sensor.

That was going to be my next step.

Time to break out the RENIX scan tool....er i mean Ohm/Volt Meter

 

[xjtrailrider]

Joe, i recently hooked up the EGR after an extended "test" period without it. Could the recirculating exhaust be heating the intake to the point of heat soak?

 

[joe_peters]

Joe, i recently hooked up the EGR after an extended "test" period without it. Could the recirculating exhaust be heating the intake to the point of heat soak?

I wouldn't think so, particularly if the EGR is operating properly (open/close).

Got to thinking though. Would you happen to have a cracked exhaust manifold, maybe up top at the runners, or a manifold gasket leaking around an exhaust port? There might be enough heat from there to actually cause a heat soak problem.

Pull the plugs and see if one or more show an odd burning condition.

EDIT: I'm getting old. Have you tested the EGR system? If not, I can find the link for the test procedure for you.

 

[xjtrailrider]

I wouldn't think so, particularly if the EGR is operating properly (open/close).

Got to thinking though. Would you happen to have a cracked exhaust manifold, maybe up top at the runners, or a manifold gasket leaking around an exhaust port? There might be enough heat from there to actually cause a heat soak problem.

Pull the plugs and see if one or more show an odd burning condition.

I'll do that next, you might be on to something there.

 

[88 Wagonman]

It sounds to me like an injector is sticking open when shut off, do like Joe said and see if one of the plugs are wet.

 

[DesertRunner]

what 5.0 did you pull the injectors off of? a stock 5.0 has smaller injectors than our jeeps if it was a cobra "blue tops" or a 460 truck it will have a larger injector 24lb

i built a stroker on my last xj it ran fin with stock injectors in cold weather give it a warmer condition say summer it would run fine till you shut her off let her sit for a few mins and the shit would hit the fan tossed the larger injectors in and that helped alot.

 

[joe_peters]

what 5.0 did you pull the injectors off of? a stock 5.0 has smaller injectors than our jeeps if it was a cobra "blue tops" or a 460 truck it will have a larger injector 24lb

i built a stroker on my last xj it ran fin with stock injectors in cold weather give it a warmer condition say summer it would run fine till you shut her off let her sit for a few mins and the shit would hit the fan tossed the larger injectors in and that helped alot.

Good point. On a stock 4.0 you would want 19 lb injectors.

Leave the bigger injectors for the strokers with an adjustable MAP.

 

[xjtrailrider]

I have the Yellow top injectors. It runs great other than this hot start issue.

 

[joe_peters]

I have the Yellow top injectors. It runs great other than this hot start issue.

The yellow tops should be fine.

Let us know how the plugs look.

 

[xjtrailrider]

I pulled the plugs today, they look new. I put them in there less than 1k ago. I did unfortunately break a expensive plug wire terminal in the process (LiveWires). Its always something!

Plugs 1-2

plugs 3-4

Plugs 5-6

I plan on getting it hot tomorrow and try to emulate the "hot/crank but no start" scenario and check the CPS.

 

[DesertRunner]

i see alot of new parts in your pictures! have you been chasing this problem? i think i see a new map and fuel pressure regulator?

what have you replaced?

 

[xjtrailrider]

i see alot of new parts in your pictures! have you been chasing this problem? i think i see a new map and fuel pressure regulator?

what have you replaced?

No issues until this. This Jeep has been fully resto-modded including the freshly rebuilt original 4.0. I have about 20k on the engine and restoration. Everything under the hood is new.

The issue started with the 5.0 injectors and new EGR valve. Both items were added at the same time. It ran fine before that.

 

[xjtrailrider]

Ok, I did some tinkering tonight.

CPS ohm reading was 255 hot/cold/didn't matter, stayed nailed to 255

No crack(s) in the exhaust manifold

The injectors are not leaking, I have pressure on the rail (key off) when the issue is happening and it starts fine cold.

I really think its just too hot under the hood for the Ford injectors. I found that if I open the hood for only a minute it will start up easier but still run rough until the fuel cools injectors. Right now I have dual electric fans operated off of the stock temp sender in the radiator. I might change that and have one of the fans on with the ignition to keep things cooler under the hood.

Still looking for a solid answer.

 

[88 Wagonman]

When you are having the problem, test the spark by pulling one of the plug wires from the plugs and using a spare plug gounded to the block check for spark. If you have no spark then you can rule out the injectors. If you have spark then try spraying a little carb cleaner in the throttle body and see if that helps.

 

[jeeperjohn]

Maybe some header wrap would help or some of those spark plug boot protectors put over the injectors? Hood vents help too.

 

[xjtrailrider]

Maybe some header wrap would help or some of those spark plug boot protectors put over the injectors? Hood vents help too.

I thought about the wrap, might do that anyway. No hood vents for this ride, it has 3k worth of paint on it.

 

[88 Wagonman]

Looks nice, but for 3k they couldn't even get the emblems in the right spots?