Car starts to missfire/wont rev beyond 4.5k RPM

[Killtodie]

Problem Has Been Solved!

I would like to thank everyone who has helped out, I was finally able to get it resolved.

What was it? Air intake system After installing the new *DM hardpipes and intercooler the car had no more problems revving. It wasn't the MAS or any electoral or sensors. Car runs great now, cept for my newly discovered worn clutch.

 

I noticed many other people have a similar issue, explore this topic, your solution is in here somewhere.

 

 

 

 

 

 

Bought the car, drove it home for 12 hours. I know that I babied the car on the drive so I cannot recall if this issue was from the get-go.

 

Main Issue

The car will start to miss-fire or sometimes not rev beyond 4.5k RPM. Before I replaced the Throttle Body and fuel injectors it would simply not rev at all beyond 4.5k RPM

 

First thing I replaced was the whole air can. Original had a ripped accordion hose and was just beatup.

Unrelated repairs: New water pump, radiator, PS pump, all belts and vacuum lines, suspension, brakes, sway bars, endlinks, brake lines, wheels, tires....

 

Replaced the following

Each one replaced made the car run smoother

-Spark Plugs, Autolites

-New oil, engine, tranny, LSD. Royal Purple all around, 20W50, 75W120

-Ignition Wires

-Rotor cap

-Distributor Rotor

-Vacuum Advance

-Throttle Body

-New Fuel Injectors

-Injector Clips

-Tank Fuel filter

-Fixed kink in fuel line

-Coolant temp sensor

-Many hoses

-All vacuum lines

 

Temporally replaced

These made no change

-Ignition Coil

-MAS

-Played with timing (had no timing light though)

-Wastegate, played around with max PSI

 

Update

-Replaced spark plugs with Autolites, no change

-Replaced entire air intake and IC with hardpipes, 1G MAS, not fully installed yet, need to clamp everything, solder new MAS plug get a BOV.

-Will replace/cleanup the fusebox and all fuses

-Will fix broken temp sensor plugs

-Engine Bay fuel filter (haven't run car since, installed PSI gauge)

Right now the car isn't running since I haven't finished installing the air intake.

 

What's In It Now

The car has a straight 2.5 exhaust, removed all emissions related devices. Jet valve delete. Engine was rebuilt by previous owner, I do not know if it was bored out or if piston compression was changed. The balance bar has most likely been removed.

What else could be causing this? Car does have some electrical issues, for example there was a wire running from the + Ignition coil terminal to the windshield wiper motor, it has been removed.

There are some weird wires running from the O2 sensor and I had a wire running from the sensor on the thermostat housing to another wire that is normally too short to reach that sensor.

The car has minor electrical issues, bad contacts on rear hatch (need to clean those) windshield wipers on intermediate mode get stuck sometimes, not sure if the motor and levers need to be greased or what.

 

I was looking at the distributor coil one day when replacing my vacuum advance, it looked fine, springs worked, sprung back no problem. Seemed a little tough but I think its working fine.

Engine also works well, miss-fires a tad bit when first started but after RPMs goes down its smooth

 

What could it be?

-Fuel Delivery? Fuel pump is aftermarket and sound like its working fine, although I did not yet test fuel PSI.

-Exhaust? The O2 sensor has been moved further down the pipe.

-Electrical Issues of some sort? Fusible links are exposed, working on replacing them

-Turbo? Doesn't seem to have any play.

-Wastegate?

-Distributor? Can it not actuate the vacuum advance properly?

 

What's Next

-Do a timing check (trying to buy a spark light check without spending big bucks on a timing light, no auto retailer sells one locally)

-Run car with new air intake

-Look over electrical components

 

Please help me out with my problems, I will keep this post update with each thing I try.

See my sig for my repair progress, lots of pictures.

 

Thank you

Edited November 25, 2009 by Killtodie

[FRO]

ive had the exact same problem, took me a year to find it.

 

 

the tank is probably rusted out

 

 

its is a common ploblem when the cars sit for years...

 

 

theres an inspection door in the trunk dr. side. pull the pickup tube out, there is a screen on the end. check out the tank while ur there..

 

 

 

hope this helps

[Killtodie]

Took the tank out, replaced the filter inside. Looked inside, it was clean, got rid of some tubes and that plastic box off it...

 

The fuel filter inside it was clean anyway.

[cyberquest]

whats your fuel pressure? have you tested and reset the ISC and TPS?

[Killtodie]

whats your fuel pressure? have you tested and reset the ISC and TPS?

 

 

No I have not. I need to pick up me a PSI gauge.

Whats an ISC and TPS and how do you reset them?

Edited August 22, 2009 by Killtodie

[FRO]

if the tank is clean then great one less thing to worry about

 

 

find a way to check the fuel pres.

 

you replaced the fuel pump right?

what about the filter?

 

 

[Indiana]

The NGK plugs, what number is on them?

Is this using the original coil?

"Replaced" injectors, what does that mean exactly have those been professionally cleaned or are they brand new?

 

I'd try making the gap a little smaller, say .038 and if you could go get an MSB Blaster II coil (about 15-20.00) just make sure its for electronic ignition.

 

What does your knock sensor look like? Are the guts of it exposed? If they are, flush it with some brake/carb cleaner and fill it back up with silicone.

 

The TPS, if its out of adjustment that can either mean the ECU won't see that the throttleshaft is at idle or wide open throttle because it only has so much range of movement and there is adjustment for it. Its a black thing on the end of the throttle shaft. When the engine is warmed up at idle it must be at or below .5volts. When you press the gas pedal to the floor that has the TPS at 4.5v or a little more. 4.5v tells the ECU the throttle is wide open and to stop using the 02 sensor and dump in as much fuel as the WOT fuel map can.

 

When under boost and high rpms, there has to be enough fuel present and the ignition timing can't be too far advanced, that fuel has to be burned and if the ignition system is weak or the mix is too rich that it will not burn and you have a misfire. Excess fuel is dumped into the exhaust and the plug gets wet. Being rich and a misfire isn't going to cause knock. Being lean or having too much ignition timing can cause knock and the ignitor can pull timing back and cause the car to jerk or buck then it will continue on or do that again. If it keeps on doing it many times one after another its likely not knocking and its a misfire from fouled plugs, being too rich, plug wires that are tangled and the spark jumps from one wire to another and not to the plug.

 

What fuel pressure regulator you have?

[Killtodie]

The NGK plugs, what number is on them?

Is this using the original coil?

"Replaced" injectors, what does that mean exactly have those been professionally cleaned or are they brand new?

 

I'd try making the gap a little smaller, say .038 and if you could go get an MSB Blaster II coil (about 15-20.00) just make sure its for electronic ignition.

 

What does your knock sensor look like? Are the guts of it exposed? If they are, flush it with some brake/carb cleaner and fill it back up with silicone.

 

The TPS, if its out of adjustment that can either mean the ECU won't see that the throttleshaft is at idle or wide open throttle because it only has so much range of movement and there is adjustment for it. Its a black thing on the end of the throttle shaft. When the engine is warmed up at idle it must be at or below .5volts. When you press the gas pedal to the floor that has the TPS at 4.5v or a little more. 4.5v tells the ECU the throttle is wide open and to stop using the 02 sensor and dump in as much fuel as the WOT fuel map can.

 

When under boost and high rpms, there has to be enough fuel present and the ignition timing can't be too far advanced, that fuel has to be burned and if the ignition system is weak or the mix is too rich that it will not burn and you have a misfire. Excess fuel is dumped into the exhaust and the plug gets wet. Being rich and a misfire isn't going to cause knock. Being lean or having too much ignition timing can cause knock and the ignitor can pull timing back and cause the car to jerk or buck then it will continue on or do that again. If it keeps on doing it many times one after another its likely not knocking and its a misfire from fouled plugs, being too rich, plug wires that are tangled and the spark jumps from one wire to another and not to the plug.

 

What fuel pressure regulator you have?

 

Trilogy Turbo Injectors, plugs are 3903 heat rating 6. I swapped out for an aftermarket coil, it made no difference.

What is a knock sensor and where is it located?

 

The Throttle body has been replaced and I believe when that was done the TPS had been looked at.

 

I did not replace the fuel pump, the current is an aftermarket one, I cant remember what brand. It has been replaced by the previous owner, it makes lots of noise and sound healthy (when the rear panels are removed)

 

I really do not want to remove the spark plugs, they have a crush washer. When I removed the autolites that were in there before and put them back in, oil started to leak out the threads, I re-tightened them and cleaned out the washer and oil still leaked until I replaced the plugs themselfs. Old plugs werent in bad shape, just couldnt find autolites anywhere.

 

I dont think the engine runs lean, exhaust isnt glowing and no smell of fuel coming out of the exhaust.

 

Could this be an distributor issue?

 

I also really dont want to spend buy parts unless they are broken 100%. Just spent $60 on a new vacuum advance that made no difference, had the old one tested plenty of times but people suggested to get a new one anyway.

Edited August 22, 2009 by Killtodie

[Indiana]

The plugs are too hot and have that tiny point to fire from and that heat range is for a non intercooled car running low stock boost but they weren't those Iridium plugs get those out of there they suck. Plugs that fire with such a fine point, that focal tip, are going to be much more likely to foul out as the rest of the plug isn't being burned. Just the change in a couple psi made Mitsubishi change to one step colder plug for the intercooled cars -to a 7 You are likely both misfiring and maybe detonating and the knock sensor doing its job. On NGK plugs the lower the number the hotter the plug, others are opposite. Either get plain BPR7ES or the OEM installed ones BUR7EA. Those BUR7EA plugs, they can fire to the tip or to the side where ever the best path is and that will keep them from fouling out as easily and that's the way there were made and Mitsubishi knew that and used them.

 

Read what NGK defines as semi surface discharge plug what was OEM installed in your car.

 

http://www.ngk.com/sparkplug411.asp?kw=Sem...arge&mfid=1

 

 

They look like this

http://photos-e.ak.fbcdn.net/hphotos-ak-snc1/hs123.snc1/5289_1027208978663_1778479606_56212_606787_n.jpg

 

That ground ring being so close to the electrode keeps the crap from getting in the gap and also lets the spark go there is the tip is compromised. You can get those online just search that part number.

 

 

 

 

http://www.ngk.com/glossaryImages/67.jpg

Bridging

 

Bridging happens when deposits accumulate between the center electrode and the outer shell or base of the ground electrode. These deposits can form a "bridge" for an improper spark path from the center electrode to the outer shell. The accumulation of deposits on the firing end can be caused by oil leakage, fuel quality and the engine's operating duration. Depending on the application, there are a variety of self cleaning designs used by NGK to reduce bridging.

 

The car does have fuel pressure surges from boost, the rpms may be low in you are in higher gear and boost build at WOT the fuel may not be burnt. The oil mist coming from the separator that can end up entering the intake and burning could make cardon deposits and Mitsubishi knew all this. They chose that spark plug for a reason.

 

This picture is from the 88 service manual

http://photos-h.ak.fbcdn.net/photos-ak-sf2p/v5206/244/80/1778479606/n1778479606_70423_1911684.jpg

 

 

jegs and summit carry them...

http://www.jegs.com/i/NGK+Spark+Plugs/739/BUR7EA-11/10002/-1

[Starfighterpilot]

I have something to add to Indiana's post above.

 

You NEED to pull the plugs and check the gap besides getting a new set of NGK BPR7ES or the OEM installed ones, Denso BUR7EA.

 

What you are describing is what I am looking for when I am setting the gap in my spark plugs. Spark blow out from too wide of a gap.

 

Typically I set the gap intentionally narrow to 0.033" Then I do power runs, increasing the gap by 0.001" each time until you get hard acceleration with a miss-fire. When you get the miss-fire, drop back the 0.001" to when you didn't get it. (Each engine is different and you are tuning to YOUR PARTICULAR engine).

 

One other question. Have you figured out why you are getting oil at the cylinder S plug holes? Have you done a cylinder pressure leak down test or at least a compression pressure test?

 

I suggest that you trace down the root cause of that oil at the S plug holes. It may be rings, valve seals, or valve guides. Eliminate the rings first then work from there. The root cause of the high RPM hard acceleration could be from a fouled S plug(s) like Indiana said. You won't correct the mis-fire from the oil fouled S plug(s) until you correct the root cause.

 

For What It's Worth.

 

KEN

 

[Killtodie]

I just found the old box, the ones I bought from Pep Boys are BPR6ES-11.

 

Should I get the 7s instead? I just spend $20 on these plugs about a month ago. Is this really my problem? I'm trying to keep cost down.

 

 

I do not know why I am getting oil out of the plug holes. As I said, the engine was rebuild by the previous owner. I do not know to what extant other than new pistons, bearings and a new crank was installed. The engine runs very smooth. The car might be burning oil, hard to tell. The level fluctuates on the dipstick. Might be just uneven ground. In the last week I did burn a lot more oil, but it was a lose rocker cover that I didn't tighten down all the way.

 

Am I going to need to remove the exhaust and intake manifolds to pop off the head to inspect the cylinders and seals?

Edited August 24, 2009 by Killtodie

[Indiana]

Oil from a leaking valve cover gasket will end up under the plug, you remove them and it gets on the threads. Black color on the plugs maybe oil in the intercooler from before, or coming through the separator. You don't need to pull manifolds or the head just remove the intercooler and wash it out with some solvent. Seal the valve cover gasket and check for leak. Get the PCV valve sealing (OEM) and the separator cleaned out then put in the plugs and go from there.

 

 

[Killtodie]

The oil on the plugs was not from the leaking rocker cover. I observed oil bubbling out of the threads around the plugs. After replacing the plugs that came with new crush washers I no longer had oil coming out of that.

[mikec]

The oil on the plugs was not from the leaking rocker cover. I observed oil bubbling out of the threads around the plugs. After replacing the plugs that came with new crush washers I no longer had oil coming out of that.

That sounds more like a small puddle of oil leaked from the valve cover gasket to settle into the spark plug depressions... then engine compression & combustion pressures pushed pass the old/missing spark plug crush washers making bubbles in the oil. If oil really does "come from" the combustion area, past the spark plug threads to accumulate in the plug depressions that means there is a significant oil leak INTO the cylinders - there should not be oil in the combustion chamber area. Just a very very small amount from the crankcase oil separator system though; that should not be enough to accumulate and "make bubbles" unless you watched it for 1000+miles of engine running.

 

mike c.

 

[Killtodie]

That sounds more like a small puddle of oil leaked from the valve cover gasket to settle into the spark plug depressions... then engine compression & combustion pressures pushed pass the old/missing spark plug crush washers making bubbles in the oil. If oil really does "come from" the combustion area, past the spark plug threads to accumulate in the plug depressions that means there is a significant oil leak INTO the cylinders - there should not be oil in the combustion chamber area. Just a very very small amount from the crankcase oil separator system though; that should not be enough to accumulate and "make bubbles" unless you watched it for 1000+miles of engine running.

 

mike c.

 

 

I am fairly certain that that is not the case. I re-tightened the rocker cover, I removed the plugs, I cleaned out the holes, reinstalled the spark plugs and there was oil bubbling after a few minutes from their crevices.

Video

 

Only after I installed new plugs with new crush washers did it stop leaking. When I had a previous thread about choosing the right plugs, I mentioned this problem and it wasn't of concern to anyone.

 

I dont know though, its not burning much oil now, but it did burn almost all its oil when I drove it home for 650+ miles.

 

You tell me what this could be

[Killtodie]

so get BPR7ES or not?

[Indiana]

I watched that video and some others, is that the same car?

[Killtodie]

I watched that video and some others, is that the same car?

 

same car, might have been taken a few days apart between replacing parts

 

there are video's of the test drive are of another car

Edited August 25, 2009 by Killtodie

[Indiana]

Jet valve delete. Engine was rebuilt by previous owner, I do not know if it was bored out or if piston compression was changed or if the balance bar had been removed.

You get this car from someone on here that knows more about it? Those other videos is this the same car and how about that "test drive starion"? That car has a dead/dying turbo in it and a power steering leak. You have a non working PCV valve and a separator and you can burn that much oil in 650 miles and what was in the PCV hose after the PCV valve? Was that a check valve and could have been in backwards? The oil feed line is behind the coolant line on the turbo meaning its been bent quite a bit does it have a kink in it? What are the compression numbers on this motor? You checked the timing because in that video where its started that sounds like the starter kicking back meaning the timing is way off. Are these new things you have did to it when you said hoses removed or was this that way it was when you bought it?

[Killtodie]

The test drive video is NOT of my car.

 

The previous owner is a member here who hasn't logged and had ignored all my calls since the sale.

[Indiana]

Its hard to remember what each car had done to it and its issues without some review but I did see where you said it had a loose valve cover. That oil you saw on the plugs was there and it couldn't be wiped away or go away unless the plugs were removed and it was wiped out. Plug may have been loose but likely it was just laying down in there from before or it was there from before and a loose plug caused that to bubble but oil isn't going to directly leak from a plug hole unless the motor is burning massive amounts of oil and then those plugs will be all black and crusty which may be the case if you won't remove them to look. Crush washers can be used over and over you just tighten them a bit more is all. There isn't enough of a leak even from a loose plug for you to know it or have a misfire. I'd check every hose you have left to make sure its in the right position and you mentioned you just "replaced" the MAS what did that mean? Did it have a 1G MAS or is the plug hacked because if it is you can plug that in upside down and cause that issue too. On the hoses, you need the one for the wastegate over at the over valve cover pipe and you need the one from the vacuum advance to the forward most of the 3 in a row on the throttlebody and NO others are necessary to drive the car. If you have a BOV or BOOST gauge you need a place to hook that up, if you want the a.c vents and cruise to work you need the one on the very most lower TB port that goes back along the firewall.

 

All the rest on the TB MUST be capped. thermo valve, egr, charcoal tank etc doesn't matter what you do to those but you can't have any vacuum or boost leaks. What was that thing in the PCV hose I saw on one video but was removed in another? Looked like some form of check valve.

 

You MUST use a timing light you can't guess at ignition timing you may have just that issue along and the knock sensor is preventing you from rev'ing higher. Go Rent borrow or something but get that set properly. Check the compression and you need to inspect those plugs and don't worry about crush washers not sealing again. People pull and inspect plugs to read them 20 times it won't make any difference.

 

I find timing lights at flea markets or thrift stores frequently, I just got an old strobe light type at at Goodwill for 4.99 last evening.

Edited August 25, 2009 by Indiana

[Killtodie]

That video is old. All the vacuum hoses have since been replaced.

 

1. Buy Timing light

2. Adjust timing

 

 

Besides that, do you think that my current spark plugs could be causing this? Should I buy the 7's instead of the 6's? I can remove my current plugs and post their pics here and you can tell me what condition they are in or if there are signs of oil getting into the combustion chamber.

[Indiana]

I'd at least inspect them. The heat range of that plug is wrong for your car. There is a combustion temperature increase/decrease from going one step colder/hotter on the plugs and you don't want to go to the hot side

 

http://www.ngksparkplugs.com/techinfo/spar...gs/techtips.asp

 

read a bit from that link

[Killtodie]

Well if they are wrong than I should replace them, correct?

 

I'll inspect the old ones tomorrow after work and post some pics, go from there.

[Motorking]

Hello,

I am a technical advisor for Autolite Spark Plugs. I am also in the process of installing a LS6 engine in a 87 Conquest in my shop MotorKingRacing. (Sorry about the LS6 guys, it's what my customer wants.). I am reading your post and have some questions before offering advice. Is the car "falling flat" above 4500 prm's or does it misfire? If it falls down, it is likely fuel and you really need to check both fuel pressure and volume.

You can buy a fuel pressure tester for 50 bucks that will let you see pressure and has a dump to check volume.

You should have 47-50 psi at idle with the vac line disconnected from the regulater, it should be 38 psi at idle with regulater connected. If it passes these tests, check volume by putting dump hose in a clean container, dump fuel while engine is idling, if it continues to run while fuel is dumped, volume is ok.

 

If it misfires, it is a lack of ignition under a load. It could be as simple as cutting down your plug gaps. I have built over 100 boosted cars in my shop in the last 10 years, mild boost increase, stock plugs and gap, more boost, one step colder plug with a decrease in plug gaps. Many ofm the late model LS and Ford Mod motors we do are running .025-.030 plug gaps. Try using a iridium fine wire plug like Autolite XP. They take less voltage to fire due to the construction and metalugy. I will send you a set free to try if you like.

 

What really worries me is your oil usage. You should most definately do a compression and leakdown test on this vehicle before throwing more parts at it. Unless you know it is sound from that standpoint, no amount of tuning will fix it! Excessive oil vapor in the combustion chamber not only lowers octane rating of the fuel your trying to burn, it also increases the chances of detonation tremendously.

Good luck.

MotorKing