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Discussion Starter · #1 ·
I have a badly behaved 1999 Lightning (137k miles) that is giving me a real hard time............and I'm running out of ideas.

When I got the damned thing, it was running bad, misfiring and making next to no power, and it had a couple of trouble codes.
I changed out the spark plugs (poor condition), Injectors ( also looked sketchy) and coils (Mis-matched and old).................all bought from Rock Auto.
Then cleared the codes and went for a test drive.

General running was immediately improved but it had a horrible off idle stumble / hesitation.
Other than this, it was pulling strongly and making good power / boost................but NO CODES when scanned.
The intake and throttle body, etc were full of oil, as per usual...............so I removed all this and cleaned up the whole lot and re-fitted with new gaskets.
Along the way, I discovered a very suspect vacuum hose which was hanging together by a thread was was almost certainly causing an air leak, so I fixed this also.

Since the oil seemed to be getting sucked up from the pass side PCV circuit, I plugged the third hose leading down to the turkey pan at the top, near the tee piece and plugged its counterpart in the PCV line. I also plugged the pass side PCV and left the PCV socket in the valve cover open to atmosphere. My thinking for this was to at least temporarily prevent the intake pulling oil into the freshly cleaned induction system.

With high hopes for a good result, I took the Lightning for another road test and, if anything, it was even worse.
If it was a carburettor car, I'd say it was getting a lean fuel condition as the stumble was at least as bad as it was and it now felt like it was holding back power wise.
There is also the occasional sneeze back through the intake system if you try to "power through" the stumble.
However, still NO CODES this time around.

I thought I was moving in the right direction when there was a vast improvement after changing out the plugs, injectors and coils but now the Lightning runs so much worse now that the induction system isn't full of oil (lol) that it definitely feels like I've taken a huge step backwards,

Can any of you wise Lightning owners help me with some advice with this truck as I am, as I said running out of ideas..................?
 

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Dude
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Have you read through the how to part on vaccum line routing and PVC valve hook ups? You cannot plug PC valves as that is how the engine breathes

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Discussion Starter · #3 ·
Have you read through the how to part on vaccum line routing and PVC valve hook ups? You cannot plug PC valves as that is how the engine breathes

Sent from my SM-G950U using Tapatalk
Yes I have........that's why I left one of the valve covers open to atmosphere so that crankcase gases could at least vent.
I also tried leaving the unplugged PCV valve to atmosphere, rather than plugging the line off, so that it's just pulling clean air in and not oil.
Do you think this is having any effect on running, other than venting oil mist into the engine bay if I left it like this..........?
 

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Dude
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It does make a difference in the intake and vaccum, drivers side need to be hooked up. If you plug the Turkey pan and run everything as normal, it should be good.
Also make sure your Boost bypass actuator is working if it is stock, there are 2 hook ups to the actuator. 1 from the mid plate and 1 from the intake

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Wile E. Coyote, Super Genius!
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Driver's side has to be hooked to the elbow, or the engine is drawing in unmetered air, which results in P0171/174 lean codes. I tired going with breathers on both valve covers years ago, nothing but trouble. I now have the elbow on the back of the block deleted and an oil separator in between the PCV valve and the plenum. With an oil separator in line, the oil problems go away. I just have to remember to drain mine every so often. It fills up fairly fast. It has a valve on the bottom, place an old rattle can lid under it, open it, drain the oil, close it. Have to remember to close it, it is a major vacuum leak if you leave it open. Ask me how I know this! LMAO!!
 

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Leaving a valve cover open to atmosphere without a tune adjustment can cause a lean condition. Also,have you replaced the fuel filter? Thats a cheap option that could fix current or prevent future problems.
 

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Discussion Starter · #8 ·
It does make a difference in the intake and vaccum, drivers side need to be hooked up. If you plug the Turkey pan and run everything as normal, it should be good.
Also make sure your Boost bypass actuator is working if it is stock, there are 2 hook ups to the actuator. 1 from the mid plate and 1 from the intake

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So, can I ask (because I cannot actually see) is the connection to the turkey pan actually connected to the plenum, and therefore subject to whatever boost / vacuum the induction system is making................or is this connection simply a crankcase vent..........?
 

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Professional Lackey
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Does what mods does it have if any? Is there an aftermarket lower on it?

The first thought in my mind is the tune is fudged up somehow. But that’s all dependent on if it has any mods to require a different than OEM tune.
 

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Discussion Starter · #11 ·
Does what mods does it have if any? Is there an aftermarket lower on it?

The first thought in my mind is the tune is fudged up somehow. But that’s all dependent on if it has any mods to require a different than OEM tune.
As far as I can make out, the Lightning is stock and unmodded................but since I have nothing to compare it to, I don't know for sure.
Who knows what someone has done to it in the past........?
What I don't get is why no DTC codes come up..........?
 

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MY fuel pressure is high 30's (37-38) with key on engine off and about 32-33 at idle .
As far as I know, that's in the ballpark for stock, right..............?
Yes, very good. Most people try diagnosing a problem without ever checking fuel pressure. Good job.

So now you can move on to proper diagnosis. Vacuum leaks, bad connections, compression and leak down test along with data logging to see how each bank of cylinders is being fueled.

JJ
 

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Try posting a picture of the lower pulley so we can see if its stock or not. Also, get a tape measure or a ruler and measure the upper pulley and take a picture of the measurement.
 

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Discussion Starter · #15 ·
Try posting a picture of the lower pulley so we can see if its stock or not. Also, get a tape measure or a ruler and measure the upper pulley and take a picture of the measurement.
Couldn't get a decent picture of the lower pulley but it measures 8" or 204mm diameter.
The upper one is 3 1/4" or 82mm.
With boost in mind, the factory boost gauge registers 10+ lbs of boost when motor is given some beans.
Would this be correct for a stocker and is this gauge to be trusted..........?
539425
Auto part Tire Automotive tire Vehicle Suspension
 

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Wile E. Coyote, Super Genius!
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If that is eight inches to the outside of the belt "grooves", it sounds like a stock pulley. The stock lower is a 7.5 inch, and the surfaces on the edge are about .25 per side. You have to actually be able to measure the surface the belt rides on. The stock Lightning upper is listed as a 2.93. So yeah, after including the surfaces at the edges, 3.14 would be pretty close.

I have a stock upper at home, I'll measure it later. Anyhow, a stock lower is a unique arrangement. There is the pulley being retained by one large allen bolt through the center. And three octopus arms radiating out from that attached to the block. Almost all aftermarket pulleys are retained to the engine by an adapter that bolts to the flywheel with three allen head bolts. And then the pulley mounts to the adapter with six bolts.
 
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