Problems With SN95 5.0L.... Please Help

[BowTie Eater 5 Liter]

here are the symptoms, when we first put the engine in the truck, it performed flawlessly(without o2 sensors, since they have been put in the engine has ran worse and worse) which led me to think the timing chain may have skipped a tooth, but others dont think it is the timing chain.
-Rough, inconsistant idle, it usually idles high, then will drop low, on the verge of stalling
-No Throttle Response when cold(and sometimes warm) if i give it any throttle, it hesitates, sometimes a "pop" from underhood is herd, like a backfire through the carb. this USUALLY goes away when the motor is warmed up
-Detonating(only happened once) temp gauge said it was a little over 190, running 87 octane, and it was detonating, so i let it cool down for a while.
-Seems like no fuel was getting to the motor this weekend out, it was on a bit of an angle, and it would not start(turned over, but did not fire) or when it did fire, it started, then automatically shut off after about 1-2 seconds. i thought it was no fuel, so i had a friend listen to the pump as i cycled the key, and he said it was turning on.
-when it is warm, it runs fairly well, sometimes it will be lagging a bit, then all of a sudden you can feel more power, without me pressing on the gas, it just picks up a bit from cruzing speed for no apparent reason.
-i can unplug the IAB valve, and the idle drops a bit if its idleing high, if it is at a normal idle, it doesnt affect the idle at all
it wont stay running if i unplug the spout connector
-under the dist. cap i found a burnt spot around the #1 lead, so i figure its a bad wire or plug(*resistance in there somewhere)

ive changed the iab valve, that did nothing, sprayed either to try to find a vaccum leak, nothing, changed the coil, nothing, changed the wire to the #1 cyl hoping that would do something, nothing.

i am going to do cap, wires and rotor this week hopefully, and set the engine timing to 10*btdc

i have no emmisions control stuff on this motor.

please let me know what you think it may be, or what to check, i really dont want to take it into a mechanic, but if i cant work these bugs out, its looking that way.

Thank you very much,
Kris

[redsn95vert]

if you don't have any emissions equipment and are running a carb, why are you running o2 sensors. Just take them out and plug them with pipe plugs. That should solve you're problem right there

[BowTie Eater 5 Liter]

not running a carb, kinda stumped where that came from?

but its got the whole sn95 computer andwiring and everything?

[blackEagle]

The problems you describe sound like 'open loop' issues. The EEC is trying to set cold start idle but, with no O2s or EGR, it's freaking out.

Did you scan for codes? Are you using the 95 EEC? Since you deleted the emissions sensors, you may need a chip to tell the computer not to look for them.

Also are you using the stock(94/95) MAF and TB? The TPS could be failing and the PIP in the distributor could be failing as well.

[BowTie Eater 5 Liter]

stock maf and throttle body. what i dont understand is though, why did it run perfectly after we swapped it into the truck, and now it runs like a pos? can i just reset the tps to .98? what is the PIP in the distributor?

[blackEagle]

Originally Posted by BowTie Eater 5 Liter

stock maf and throttle body. what i dont understand is though, why did it run perfectly after we swapped it into the truck, and now it runs like a pos? can i just reset the tps to .98? what is the PIP in the distributor?

The 94/95 EEC has adaptive learning strategies built in. When you clear it out by disconnecting the battery, it re-learns and stores the various sensor values in the KAM(keep alive memory).

There are tables in the EEC with minimum values so the car can start and run but the computer makes adjustments using the sensor input and the updated values are stored in KAM.

The TPS voltage is set on startup on a 94/95 and used until the next startup which resets the TPS voltage. A worn TPS can cause the bad drivability you state.

The PIP or 'Hall effect' module tells the EEC when cylinder 1 is at TDC and is well known to cause problems in 94/94's when it goes bad. The only way to replace it is to remove the distributor.

The EEC has minimum/maximum values that it operates in so a sensor can be failing but, still in the range so the CEL is not tripped but the car runs like crap.

Did you scan for codes?

[BowTie Eater 5 Liter]

the codes i got were due to the egr system, and the vehicle not being at running temp. i got a tps below min. voltage code also

[blackEagle]

Originally Posted by BowTie Eater 5 Liter

the codes i got were due to the egr system, and the vehicle not being at running temp. i got a tps below min. voltage code also

The EEC is looking for the EGR sensor to check if it's working or not. Either connect it up or you need a chip or something to bypass it.

The temp issue may be related to a bad coolant temp sensor which may be preventing the EEC from switching to closed loop mode.

The TPS error is proably causing the engine to run badly since the EEC sets the TPS voltage on startup. Only fix is to replace the TPS.

Change one at a time and clear the codes before restarting the engine.

[BowTie Eater 5 Liter]

i checked fuel pressure today, at an idle it sits at about 30 or so, but if i give it any gas, it jumps up(didnt see it hit 40psi though, which is what i thought they were supposed to sit at).
when i just turn the key on without starting the truck, it jumps up almost to 35, then slowly drops, but fast eanough you can watch it dop down.

what could this be? could it be the source of some of my problems?

i ran the motor, and reved it a little and POP from the intake, like a manifold backfire from a carburated engine. i pulled various spark plug wires while it was running and noticed little to no change in the way it ran, which has me really stumped.

does this sound like my timing?

[blackEagle]

Originally Posted by BowTie Eater 5 Liter

i checked fuel pressure today, at an idle it sits at about 30 or so, but if i give it any gas, it jumps up(didnt see it hit 40psi though, which is what i thought they were supposed to sit at).
when i just turn the key on without starting the truck, it jumps up almost to 35, then slowly drops, but fast eanough you can watch it dop down.

what could this be? could it be the source of some of my problems?

i ran the motor, and reved it a little and POP from the intake, like a manifold backfire from a carburated engine. i pulled various spark plug wires while it was running and noticed little to no change in the way it ran, which has me really stumped.

does this sound like my timing?

I'm no expert but, I think your fuel pressure is too low. Stock is supposed to be 38psi at idle. You may have a bad fuel pump or regulator.

You should get this taken care of first before doing anything else. Low FP is just like leaning out the motor. NOT a good thing.

[BowTie Eater 5 Liter]

fuel pressure is about 30 at idle.

when i shut it off, the fuel pressure drops fast, i clamped off the return line with a pair of vise grips, cycled the key(it showed 49psi) 2 hours later it was over 35 still, i didnt pinch the line too hard, as i didnt want to damage it, but when i unclamped it, the fuel pressure dropped fast eanough to watch it move on the gauge.
tomorrow i will replace the regulator(should i buy a stock one or is it worth it to get an aftermarket one for a stock motor?) and if that doesnt do it, ive got a spare fuel pump.

[BowTie Eater 5 Liter]

fawking confused. when i take the vaccum off the FPR the fuel pressure goes up to 38psi, is this normal?

someone please help!

[blackEagle]

Originally Posted by BowTie Eater 5 Liter

fawking confused. when i take the vaccum off the FPR the fuel pressure goes up to 38psi, is this normal?

someone please help!

OK. 38psi with the vacum off is correct. If you're using the stock regulator, it should not bleed off pressure so fast. Aftermarket ones do experience a pressure drop quickly.

You should now check the EGR valve. My Haynes book indicates that the EGR my be causing the issues. You also may have a vacum leak as well. The book also says that the distributor may also be at fault.

Since you have no EGR, I think that's the main issue.

[BowTie Eater 5 Liter]

thanks for the replys! my tps sensor is screwed, its supposed to be at .98 volts, im getting 4.79. i was told this could be the problem of all my issues, running like crap, running rich, and bad idle.

so im off to replace the tps!

[blackEagle]

Originally Posted by BowTie Eater 5 Liter

thanks for the replys! my tps sensor is screwed, its supposed to be at .98 volts, im getting 4.79. i was told this could be the problem of all my issues, running like crap, running rich, and bad idle.

so im off to replace the tps!

Glad you found it. Keep us informed.