408 needs help

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jbomb408

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Hey guys I have a 408 ram and I have to come to you guys becase most guys on the ram forums are of little help. I have two problems with my ram

1. When the motor was first build by my brother(sv650) the motor ripped. I could hit it from a standstill without the break and she would fry them I could feather the petal to keep her around 4000 rpm. now 4000mi latter she barely can break them loose. I know that I am running lean based on my plugs but she ran great before. My tunner says I need to dich the 24lbs. injectors for 32's. and run a retrun line with regulator. Vacume is at 17 inches and varies about a half an inch with no leaks that I can find.

The build is
408 kit form indy(mopar muscle did the machine work)
9.6 comp
512 512 cam 265 274 duration at .006 110 lobe seperation
engine quest heads with bowl work
hughes airgap intake 53mm tb
pacesetter long tube headers
2 1/2 exhaust with x and no cats.

the second issue is
2. the truck shuts off while driving and some times after a few seconds will come back on. This will happend ever other week or so. I have replaced alll the sensors and checked all the grouds. pcm is new fuel pump in new altinoator is new when the dealer had it they replaced the ignition switch and some wiring under recall. Asd is new. and still nothing. The other day while sitting in the drive it died and I was able to find that there was no spark. But she started working again before I could trace it any farther.

Thank you guys soo much I am out of options and places to turn. I would love to put a blue M in the back window of my truck and be proud but I cant yet:(
 
Thanks guys. I have replaced the crank sensor with a mopar one after several auto parts store ones and it is still dying. the pickup plate in the dist. I just changed form an auto parts store one to a mopar one this weekend so we will see.( I have tried manipulating the wires while driving and it did not die)

What about the performance drop?



BTW the fuel pressure seems to jump almost 10 pounds either way of 50 at idle. this may be my performace drop and I will correct this in the next week or so with a new return line regulator.
 
If you have an auto trans, it's possible it's starting to slip a little, which would feel like a power loss.
 
tranny was just rebuilt.

yeah I could do a leakdown test it seems to have A lot of compression.

cant put a carb on it because its a 96 and I have stupid state of texas inspections. Believe me I have thought of it.
 
Seems like a buddy of mine had a similar issue with his sons 5.2 Dakota shutting down randomly. He did replace the computer twice and the crank sensor. It ended up being a bad coil. Cheap replacment.
 
Maybe guys. The coil is just an autoparts store one and not a high quality mopar one. Any brands that I could go with that you guys would recomend? the coil is placed just in front of the # 2 clyinder where the header comes out so it would get blasted with a ton of heat. I built a cheesey heat shield to keep header heat down and away from everything and I moved the coil up one hole untill I can build a bracket and heat shield.

The coil was 2" lower!

coil.jpg
 
Well I replaced the new coil with a mopar one and moved it up as shown in the pic and it hasnt died yet!

As for being down on power we got my air fuel very close and the tuner changed my timing and its better but not what it was with the stock intake and 19lbs. injectors. I Called hughes and they are talking with my tuner. Hughes tuner is going to look at my fuel maps and see how they look but I am leaning to it being the airgap intake is the culprit. The stocker is built for more torque.
 
jbomb408 said:
Well I replaced the new coil with a mopar one and moved it up as shown in the pic and it hasnt died yet!

As for being down on power we got my air fuel very close and the tuner changed my timing and its better but not what it was with the stock intake and 19lbs. injectors. I Called hughes and they are talking with my tuner. Hughes tuner is going to look at my fuel maps and see how they look but I am leaning to it being the airgap intake is the culprit. The stocker is built for more torque.
Click to expand...

You went from the stock barrel style intake to the airgap?
It's not going to be the intake. I guarantee that. Maybe something relevant to the intall of the intake, but not the intake itself. That's the best smallblock intake out there for a street motor.
sure you dont have a problem with vac or something like that?
It will screw with these motors BIGTIME.

Where are you pulling signal from with the map sensor?
And if so, is the hose cracked?
do you have any codes?
What is the fuel sync (cam sensor) set at?
 
Top end is crazy good tho. so if it wasnt running right you would think that it would effect tho top end also.

Last time I set the fuel sync it was at +2

Vacume is around 17 inches and doesnt flucuate more than 1/2 in total. nice and steady. tried changing it around and blocking off differnt componets but it doesnt change.

I dont know what you mean by pulling signal form the map sensor. The map sensor is new. I can double chech the hose tho.

no codes
 
Well coil must have fixed the shutting off. Now for performace.

With the stock intake and 19lbs. injectors the truck would bounce off redline from a standstill Now with the air gap, 32lbs. injectors and correct air fuel ratio the truck will break them loose and run up to 3500 rpm and hook then drop back down. If I hit it going about 10 she will just take off and not even turn the tires over. HUGE drop in low end.

I am (believe) running 9.6 to one. and have 170 psi clyinder presssure(started at 150 and with multiple crank "sessions" got up to 170.

Hughes says this is ok.

Muscle motors (did my machine work) says this is wayy to high for 93 octane and I an detnating. And my computer is probably pulling timing out.

Hughes had this issue with a guy with the same cam running 215 psi becase of the duration/ overlap of the cam was too much.

Thoughts opinions?

About ready to get rid of the 408 all together and buy a diesel
 
I dont think 170 should be an issue for detonation. I've got open chamber big blocks running 185 psi on pump 93. So a Magnum headed deal should not be a problem.
 
I think a carb and a normal distributor with no computer would really wake the 408 up.

Sure its possible to dial in the computer and F.I.--if you got the money to take it to place that can do the wotk.

Me, I go old school with it
 
I cant go carbed. Texas stupid inspections

Piston deck volume 26cc

head volume 63cc

head gasket volume 12cc

i believe my compression ration is 9.23 to 1 Not 9.6
 
jbomb408 said:
Well coil must have fixed the shutting off. Now for performace.

With the stock intake and 19lbs. injectors the truck would bounce off redline from a standstill Now with the air gap, 32lbs. injectors and correct air fuel ratio the truck will break them loose and run up to 3500 rpm and hook then drop back down. If I hit it going about 10 she will just take off and not even turn the tires over. HUGE drop in low end.

I am (believe) running 9.6 to one. and have 170 psi clyinder presssure(started at 150 and with multiple crank "sessions" got up to 170.

Hughes says this is ok.

Muscle motors (did my machine work) says this is wayy to high for 93 octane and I an detnating. And my computer is probably pulling timing out.

Hughes had this issue with a guy with the same cam running 215 psi becase of the duration/ overlap of the cam was too much.

Thoughts opinions?

About ready to get rid of the 408 all together and buy a diesel
Click to expand...

Computer cant pull timing out with knock since there is no knock sensor.:read2:
Too much overlap will DROP cylinder pressure and not increase it.

If you have a true 9.2:1 compression, the actual is going to be lower than that. detonation is definitely not a problem. The stock magnum is 9:1. If you are really only at 9:2, there is no problem.

The guy hughes mentioned was probably running too much compression for that cam in which case the opposite was happening. Not enough overlap or duration, thus an increase in cylinder pressure resulting in knock with too low an octane. The intake valve was closing too soon on the compression stroke probably in his case.

The more this thread progresses the more I think you have the wrong converter stall speed. the stock intake you were using is dead by around 4800 rpm, but makes very good torque down low. With the cam and intake the torque curve moved up. And for performance with the right converter this would be great. If the converter stalls at 2200 let's say, and your sweet spot moved up to 2500, it's going to dog out before it gets to the sweet spot. Just some thoughts.

I don't think you have an engine related issue. I think your converter is the issue.

It's late and if anyone sees a flaw in my logic, do tell....be back tomorrow.:-D
 
dodge freak said:
I think a carb and a normal distributor with no computer would really wake the 408 up.

Sure its possible to dial in the computer and F.I.--if you got the money to take it to place that can do the wotk.

Me, I go old school with it
Click to expand...

No doubt. I did the same thing. I hate the magnum EFI system. Some will disagree, and that's fine, but I hated it. It's very limited. You can add a larger injector, but that's only going to help at say WOT and make the idle pig rich. That's because the fuel tables in the computer are only tailored for the factory injector. You'd have to trim them back for part throttle and idle. This can indeed cause a power loss and was something I didnt think of earlier.

One of those superchips SCT things can help there....but they are also 400-500 bucks. I chose to go to a carb and get rid of the non-user friendly nature of the factory efi system. too bad he can't do this.

In michigan they dont test anything. I can register something that burns more oil than gas and they could give a rat's ***.
 
IMO, the issues are not engien related but ECM related. The hardest part about building a Mopar is trying to use the factory computer as tehre is little or no support from Mopar to the aftermarket in terms of access to the code. IMO, best bet is a stand alone system like Megasquirt or FAST. Yes more cash and sometimes a PITA to get set, but you can set them up... Unlike anything factory PCM related.
 

but what do you think the pcm is doing that is wrong

My air fuel is right

Timing is right

Just got off the phone with hughes and they said my fuel looked good.

And its not my Tc. I had the same stall tc in the truck when it had tons of low end. same stall now there is no low end.
 
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