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View Full Version : Engine miss after heat soak, high load


bcmaxx
02-28-2011, 09:41 AM
I just want to put this out there again, I'm sure I did before, but search didn't turn up anything. I have a 89 renix 4.0 auto. After the engine comes up to temp, or is worked hard and then shut off, upon restart it misses pretty bad, like its running on three cylinders. It smells rich when this happens and my a/f meter reads rich also. The miss will go away and meter will read perfect after you hold say 2-2500rpm for 30 seconds, or leave the engine off with the electric fan on for about five minutes and restart. Anyone? I will guarantee a flat of beer to anyone that has the fix for me. This has been an ongoing issue for about 3 yrs. And I can't think of anything I have not replaced except the ecu

Tinker
02-28-2011, 10:40 AM
Change the ECU, I drink kieths lol

bcmaxx
02-28-2011, 10:51 AM
Change the ECU, I drink kieths lol
ECU You think? I just havent heard of much trouble with the ecu on these

epic3
02-28-2011, 11:58 AM
bad plugs wrong heat range perhaps.

bcmaxx
02-28-2011, 12:56 PM
bad plugs wrong heat range perhaps.
nope, tried ngk v power, champion copper, and finally oem mopar

epic3
02-28-2011, 03:31 PM
yes but did you try a higher heat range?

bcmaxx
02-28-2011, 03:32 PM
yes but did you try a higher heat range?
no I havent, what will that do for the engine?

epic3
02-28-2011, 05:45 PM
If you over heat a plug it will misfire (giving you your rich reading) and prematurely burn out.

tchevy
02-28-2011, 07:59 PM
i doubt its the plugs. sounds like a electrical component is breaking down after a heat soak. or a leaking injector after shut down but it shouldnt take 30 sec to go away. do you loose any coolant ever?

Lazybaka
02-28-2011, 11:07 PM
sounds like it's in cold start enrichment even though it's hot
I'd say the temp sensor is getting heatsoaked (and it's how old)
after you shutdown.
got any codes ?

bcmaxx
03-01-2011, 09:00 AM
new injectors ( precision injectors), new longblock, all new sensors (cps,Air intake temp, IAC, TPS,Fuel pump, fuel filter,cap ,rotor,wires, coolant temp sensor, knock sensor, Map sensor,oxygen sensor, new revolution sensor ( reman dizzy) . Replaced all engine grounds and added two more, ran ground directly to throttle body negative. New igntion module , new coil. Truck has a new csf 3 core rad, new zj clutch fan, 15" electric cooling fan. Hood spaced and vents added. Just don't know where to go with this one....... :confused0006:.

epic3
03-01-2011, 11:20 AM
Try the plugs its the cheapest and easiest and sounds like the only thing you haven't tried and I see it happen on a regular basis with some of the high performance cars we build here at my shop.
I'm not calling your jeep high performance just sayin its possible.

Bushwack
03-01-2011, 03:10 PM
check the intake for vac leaks.

Renegord
03-01-2011, 03:16 PM
If you've done any mods to increase fuel flow (ie. after market injectors) you could think about adding an ignition box , multiple sparks give you a more complete burn.efi doesn't really let you ajust your timing like you would with a carb setup , so you have to play within the perameters of your stock ECU , an ignition box will help burn that extra fuel that could possibly be choking your engine . just a thought :confused0006: .

bcmaxx
03-01-2011, 04:30 PM
check the intake for vac leaks.
I've done the propane and carnb cleaner test along the intake runner. seems fine. Just got a smoke machine so I guess I could try that too

bcmaxx
03-01-2011, 04:31 PM
If you've done any mods to increase fuel flow (ie. after market injectors) you could think about adding an ignition box , multiple sparks give you a more complete burn.efi doesn't really let you ajust your timing like you would with a carb setup , so you have to play within the perameters of your stock ECU , an ignition box will help burn that extra fuel that could possibly be choking your engine . just a thought :confused0006: .

Can you tell me more abouts this? It is unburned fuel coming out the tailpipe. I've had guys behind me on the trail said they have had to fall back because its burning there eyes with fumes. tail pipe black. And remember same problem different engines

Lazybaka
03-02-2011, 08:42 AM
right size injectors ?

bcmaxx
03-02-2011, 08:52 AM
right size injectors ?
they are ford 5.0 4 squirters. Proven to work well on the 4.0. Had the miss with stock injectors and napa remans.

Renegord
03-02-2011, 10:30 AM
Can you tell me more abouts this? It is unburned fuel coming out the tailpipe. I've had guys behind me on the trail said they have had to fall back because its burning there eyes with fumes. tail pipe black. And remember same problem different engines
Well basically , a CD ignition box throws multiple sparks at lower RPM , usually 3000 or less , and one much bigger hotter spark at higher RPM . So it's not going to fix the fact that the engine is getting to much fuel , but it will definatly burn more if not all of it in the cylinder , instead of blowing unburnt fuel out the tailpipe , and you may even get some extra perfomance out of it . So if all your sensors are working properly , thier are no vacuum leaks , everything is as it should be , and you're still running way rich , it could just be that your ignition system is a bit lazy. the only other suggestion I can think of is perhaps an ajustable fuel pressure regulator.[cheers]

bcmaxx
03-02-2011, 11:19 AM
Well basically , a CD ignition box throws multiple sparks at lower RPM , usually 3000 or less , and one much bigger hotter spark at higher RPM . So it's not going to fix the fact that the engine is getting to much fuel , but it will definatly burn more if not all of it in the cylinder , instead of blowing unburnt fuel out the tailpipe , and you may even get some extra perfomance out of it . So if all your sensors are working properly , thier are no vacuum leaks , everything is as it should be , and you're still running way rich , it could just be that your ignition system is a bit lazy. the only other suggestion I can think of is perhaps an ajustable fuel pressure regulator.[cheers]


Thanks for your help [cheers]. I'll have to find where to get one, and what will work on my heep . I'll go good on a flat of beer if this is my fix. If not thanks anyways

bcmaxx
06-13-2013, 11:27 AM
just to update:

a newer thermostat housing,
relocating the coolant temp sensor to newer t-stat housing,
new fan shroud
aux hood mounted fan over intake
new intake air temp sensor relocated to cold air ducting
new 02 sensor
air/fuel ratio meter
adjustable map sensor
has aleviated my hot soak problem, engine runs leaner, exhaust no longer makes eyeballs burn, people following me gag. and it woke the engine/throttle response up a bit