Mitsubishi 3000GT & Dodge Stealth Forum banner

1 - 20 of 31 Posts

·
Registered
Joined
·
13 Posts
Discussion Starter #1
I bought this car thinking it needed a fuel pump. But it still runs terrible with no power, low idle, backfires slightly and stumbles badly especially when cold....when warm it improves but still has no power past half throttle.

Here is what I have done so far.

Checked engine codes. Nothing. Just a constant steady flash.

Installed fuel guage at rail. Has 40psi. So I ruled out fuel pump
Replaced idle air control solenoid
Replaced Fuel Pressure regulator
Replaced Throttle position sensor
Replaced Mass Air Flow sensor
Reset base idle screw per factor instructions while grounding the brown connector behind the battery
Replaced one O2 sensor. The front one.
Removed and thoroughly cleaned throttle body. Clean as a whistle.
Tested Cold Idle valve in hot water and it opens and closes like it should
Check everywhere for vacuum leaks by pressurizing the system slightly and using spray soap to look for bubbles. Everything is sealed up tight on the intake side.
Pulled each plug wire from the coils while the car is running. Spark is jumping fine (about an inch) from the coil to the wire on all 6.

The plugs and wires were just done by the previous owner. They look new. I guess I could change the plugs but I am skeptical that would cause my symptoms.

I was thinking maybe some other O2 sensors may be bad or also possibly the coils are not firing when under load (hard throttle)?

I hate to throw more money at it without seeing some of the engine data when at heavy load (like O2 voltage and misfire data). Is there a way to read engine data? My OBD2 computer wont do it.

My research seems to say that the 1995 did not have ECU board capacitor problems.?

Or are there any other suggestions. Thank you everyone.
 

·
3SNY - HondaTurtleFTW
Joined
·
4,745 Posts
It definitely can't hurt to check the ECU. Yes, the second gen units are less likely to have capacitor problems but it's still possible. I believe EvoScan, with a tactrix device, can datalog your engine. There may be other options though. Been almost a decade since I had to use anything other than EvoScan (have a flashable 99 ECU in my car). Double check that the wires are in the right order. Could easily have a mixed up wire throwing off the firing order which would make the car run like crap. Pick up a NOID light and test at each fuel injector to make sure they're getting the signal to fire. I'd also test to make sure they're actually injecting fuel. Should be able to hear them click with a mechanic's stethoscope. It's really odd that it's not throwing any CELs when running that poorly. Also, I don't think you can check CELs with an analog meter on an OBD2 car.

When you start the car, before cranking, does the CEL turn on? If not, could be ECU or a bad bulb for it. Does your OBD2 computer say there aren't codes as well? Also, I would consider changing the fuel filter, just to ensure you have fuel pressure while moving. My car ran fine at idle but would buck, hesitate, and run like a steaming pile of dog crap under throttle. Checked my filter, found a piece of fuel line clogging the inlet side. Replaced the filter and she ran right as rain. I would also double check the mechanical timing, making sure the cam gear marks line up with the marks on the heads, and that the mark on the harmonic balancer lines up properly with the indicator on the lower timing belt cover. If that one is off, I'd pull the accessory belts, lower cover, and check the timing at the crank gear.

Sent from my ONEPLUS A6013 using Tapatalk
 

·
Registered
Joined
·
13 Posts
Discussion Starter #4
I am in Brunswick Ohio. Thank you for the replies. I will get a noid light and check the wires. The fuel filter is new. Forgot to mention that.
 

·
Registered
Joined
·
13 Posts
Discussion Starter #5
"FluffyCow, post:


Can I update my car computer to one from a 1999 that way I have OBD2 capability?
 

·
3SNY - HondaTurtleFTW
Joined
·
4,745 Posts
"FluffyCow, post:


Can I update my car computer to one from a 1999 that way I have OBD2 capability?
Look up chrome ECU. There should be a NA option. I'm not sure as it's been 12 years since I owned an NA, and chrome didn't exist then.

Sent from my ONEPLUS A6013 using Tapatalk
 

·
Registered
Joined
·
13 Posts
Discussion Starter #7
Thank you for the advice.

Just looked it up. They have one but it is $900. A little steep for me.





Look up chrome ECU. There should be a NA option. I'm not sure as it's been 12 years since I owned an NA, and chrome didn't exist then.

Sent from my ONEPLUS A6013 using Tapatalk
J
 

·
Senior **i.e. OLD** Member
Joined
·
13,241 Posts
Just throwing this out...
Does the car still have all the cats?

A clogged cat can cause power issues.

One other thought, have you checked the timing (cam marks AND crank mark)?

Bob.

Sorry, I didn't fully read "Fluffy's" post, he mentioned the mechanical timing as well...
 

·
Premium Member
Joined
·
39 Posts
I bought this car thinking it needed a fuel pump. But it still runs terrible with no power, low idle, backfires slightly and stumbles badly especially when cold....when warm it improves but still has no power past half throttle.

Here is what I have done so far.

Checked engine codes. Nothing. Just a constant steady flash.

Installed fuel guage at rail. Has 40psi. So I ruled out fuel pump
Replaced idle air control solenoid
Replaced Fuel Pressure regulator
Replaced Throttle position sensor
Replaced Mass Air Flow sensor
Reset base idle screw per factor instructions while grounding the brown connector behind the battery
Replaced one O2 sensor. The front one.
Removed and thoroughly cleaned throttle body. Clean as a whistle.
Tested Cold Idle valve in hot water and it opens and closes like it should
Check everywhere for vacuum leaks by pressurizing the system slightly and using spray soap to look for bubbles. Everything is sealed up tight on the intake side.
Pulled each plug wire from the coils while the car is running. Spark is jumping fine (about an inch) from the coil to the wire on all 6.

The plugs and wires were just done by the previous owner. They look new. I guess I could change the plugs but I am skeptical that would cause my symptoms.

I was thinking maybe some other O2 sensors may be bad or also possibly the coils are not firing when under load (hard throttle)?

I hate to throw more money at it without seeing some of the engine data when at heavy load (like O2 voltage and misfire data). Is there a way to read engine data? My OBD2 computer wont do it.

My research seems to say that the 1995 did not have ECU board capacitor problems.?

Or are there any other suggestions. Thank you everyone.
maybe double check that the plug wires are on the right cylinders for firing sequence, could have been mixed up from the last owner ... would give you all the problems you describe
 

·
Registered
Joined
·
620 Posts
+1 for checking plug wires are correct and +1 for checking mechanical timing (including cam/crank marks and setting base timing). Sure does sound like a timing problem with the backfires and consistently poor performance.

If you are looking for a permanent solution for real-time monitoring of ECU parameters and datalogging (including scanning for codes, etc), look into BlackStealth's CANBUS converter. You use it with the torque app, i have a detailed thread on it.
 

·
Registered
Joined
·
13 Posts
Discussion Starter #11
Replaced the spark plugs and checked the plug wire sequence. Everything checks out.

Car runs terrible when cold but when the engine is warmed up it runs better. Throttles up pretty good while sitting in the driveway but no power beyond half throttle on the road.

Maybe the clogged cats idea has some merit. Just not sure if an easy way to check that.
 

·
3SNY - HondaTurtleFTW
Joined
·
4,745 Posts
Replaced the spark plugs and checked the plug wire sequence. Everything checks out.

Car runs terrible when cold but when the engine is warmed up it runs better. Throttles up pretty good while sitting in the driveway but no power beyond half throttle on the road.

Maybe the clogged cats idea has some merit. Just not sure if an easy way to check that.
Did you replace the PTU? It's backwards of usual failure symptoms but better when warm leads me to think it could be the PTU, or could be another electrical component that partially breaks contact when cold.

Sent from my ONEPLUS A6013 using Tapatalk
 

·
Registered
Joined
·
13 Posts
Discussion Starter #13
Did you replace the PTU? It's backwards of usual failure symptoms but better when warm leads me to think it could be the PTU, or could be another electrical component that partially breaks contact when cold.

Sent from my ONEPLUS A6013 using Tapatalk
Good suggestion. I just bought a used one on ebay. Trying to keep my costs down.
 
Joined
·
17,276 Posts
Did the car sit for a long time? You may want to pull the fuel pump out of the tank and make sure the tank and strainer are okay. I'd also check the cam timing just to be sure.
 

·
Registered
Joined
·
13 Posts
Discussion Starter #15
Did the car sit for a long time? You may want to pull the fuel pump out of the tank and make sure the tank and strainer are okay. I'd also check the cam timing just to be sure.
I did not pull the pump but the pressure guage I installed on the fuel rail reads 40psi consistently so I didnt think fuel delivery could be a problem....but may pressure is OK but volume is insufficient if the strainer is clogged?

Does anyone have a write up on checking the timing? Or maybe a video?

Thanks
 

·
Registered
Joined
·
13 Posts
Discussion Starter #16
OK. I just checked the timing. Pulled the plastic covers off of the cam pulleys. Rotated them a little bit and all 4 dots line up perfectly with the arrows on the valve covers. I didnt look at the crank but I am thinking that is probably fine.

Again, car runs better when warm but still not well. There is no power past half throttle and an occasional light popping sound when pedal is to the floor. When the ignition module arrives, I will put that on. I wish I had some spare coils to swap out and try.
 

·
Registered
Joined
·
177 Posts
Maybe the clogged cats idea has some merit. Just not sure if an easy way to check that.
Just replaced the cat on my truck - the symptom was no power and relentless pinging (pre-ignition). It really felt like the parking brake was stuck on... had to rev way too high just to move (automatic tranny). If you have checked everything else, disconnect the exhaust at the back end of the downpipe and go for a spin. ** I do not recomend this if you live in a populated area! **
 

·
Registered
93 NA ATX 3000gt DOHC
Joined
·
1,712 Posts
....... I didnt look at the crank but I am thinking that is probably fine.....
I tried to overlook this and not say anything, but I wouldn’t be doing anybody justice by doing so. To put it bluntly and make a point at same time I must say…. OMG ….

The most important mechanical timing with an internal combustion engine is cam timing to the CRANK. In multiple cam engines, cam timing to each other is important BUT not as important as all cam timing to the CRANK.

On these engines the most common place timing belt will jump is at crank, because it’s the smallest cog gear with least teeth engaged with belt and has most load trying to turn four cams. If that happens cam gears are still happily timed to each other, but NONE of them are timed to the CRANK (did I say that was important?:rolleyes:).

I know it’s a pain to remove every thing needed to see if crank cog gear is on mark to oil pump. But not hard to do what FluffyCow suggested
“I would also double check the mechanical timing, making sure the cam gear marks line up with the marks on the heads, and that the mark on the harmonic balancer lines up properly with the indicator on the lower timing belt cover”
which would be zero. If it lines up to the zero position all is well. If it doesn’t line up to zero that means timing belt has jumped at crank or harmonic balancer rubber bonding has allowed outer ring to slip, which means you need to remove balancer and lower timing cover to check crank cog gear timing to oil pump housing mark.

Also never turn engine crank counter clockwise, that will put slack in belt which could cause belt to jump at crank gear.
 

·
3SNY - HondaTurtleFTW
Joined
·
4,745 Posts
I tried to overlook this and not say anything, but I wouldn’t be doing anybody justice by doing so. To put it bluntly and make a point at same time I must say…. OMG ….

The most important mechanical timing with an internal combustion engine is cam timing to the CRANK. In multiple cam engines, cam timing to each other is important BUT not as important as all cam timing to the CRANK.

On these engines the most common place timing belt will jump is at crank, because it’s the smallest cog gear with least teeth engaged with belt and has most load trying to turn four cams. If that happens cam gears are still happily timed to each other, but NONE of them are timed to the CRANK (did I say that was important?:rolleyes:).

I know it’s a pain to remove every thing needed to see if crank cog gear is on mark to oil pump. But not hard to do what FluffyCow suggested which would be zero. If it lines up to the zero position all is well. If it doesn’t line up to zero that means timing belt has jumped at crank or harmonic balancer rubber bonding has allowed outer ring to slip, which means you need to remove balancer and lower timing cover to check crank cog gear timing to oil pump housing mark.

Also never turn engine crank counter clockwise, that will put slack in belt which could cause belt to jump at crank gear.
I'd like to relay a personal story. MY car shut off once while driving. I pulled everything. My balancer hash mark didn't line up with the cover indicator. When I pulled everything apart, not only did the hash not line up, it didn't line up with where the crank gear indicator said it should be, AND the crank gear did not line up either. I believe I was two teeth off. I got very, very lucky and didn't have any mechanical damage. I'd rip it all apart and check that crank timing.

Sent from my ONEPLUS A6013 using Tapatalk
 
1 - 20 of 31 Posts
Top