1G '91 AWD won't rev beyond 5500 rpm

[quickduc]

This problem has been ongoing for years.
Plugs and wires don't help. Swapped the coil from my spare engine, no change. Ignitor box, ditto. Cleaned the injectors. (removed them and soaked them in Sea Foam with a power supply to hold them open, to expose the internals for complete cleaning. Wow! What a difference in throttle response and overall performance. Like a new engine! Still won't rev up.)
I'm not seeing/hearing/feeling any boost leaks. Have not installed a real boost gauge. Just has the oem dash gauge.
Replaced the fuel pump when it started stalling below a 1/4 tank. Put in a Walbro 255?
Except for the pump, the car is stock.
This problem aggravated my father the PO, and his mechanic could never figure it out. The car would run 140mph originally. Dad had a bunch of these DSMs, but this one had him stumped.
This has been an erratic problem. When I first got it ~'03, it occasionally wouldn't rev up. Now, it is reversed, and mostly won't. Runs strong until 5500. It acts like it has a rev limiter.

Has that CARB mandated generic cat that strangles the motor, but this problem predates that by a decade or more. (I suspect that CARB picked the 420 cat for all the DSMs, as I estimated the matrix is about 63% volume of the OEM cat. Strangles that poor motor. I can understand why people take the damn things off with this sort of idiocy. Seems to hurt fuel mileage too.)
Got it with 100k miles, now ~168k.

 

[Vegas Smith]

I had the same problem and it turned it was my clutch switch. The car would start stuttering around 5500 all the time. It's a longshot but maybe unplug it.

 

[ThunderChild]

Sounds like a boost leak. Does it rev strongly to 5500, and then struggle, or does have a hard time getting any RPM?

next I'd be looking at the rest of the fuel system, maybe check TPS for proper signal.

If the cat is clogged it may be contributing, but you'd have to pull it to check.

In the end, you may want to check the ECU for evidence of leaking caps or other damage.

 

[Mello]

No profile info. Do you have a turbo with an internal wastegate. If so, check the actuator & flapper and make sure the flapper is closing all the way. You might need to adjust the actuator & rod so there is some preload to help keep the wastegate closed & and getting pushed open from the exhaust back pressure. Just another though to the other suggestions.

edit: also check for cracks in the turbine house especially around the hole for the flapper.

 

[quickduc]

The switch sounds like a possible.
Car is totally stock under the hood.
TPS has been checked and swapped before.
Replaced the Caps on the ecu maybe tens years earlier. Recently checked and they looked okay.
Brand new Cat Convertor.(see original post on this item)
Pulls strong to 5500 and then quits.
I'll check the turbo housing and wastegate linkage (and that switch) tomorrow.

 

[pauleyman]

I had the same problem and it turned it was my clutch switch. The car would start stuttering around 5500 all the time. It's a longshot but maybe unplug it.

How would this apply on a stock car? I can see it on a link equipped car.

 

[Vegas Smith]

How would this apply on a stock car? I can see it on a link equipped car.

That's true. I didn't think of that.

 

[Mike9490]

no joke i had this same issue, bugged me for a year, granted my car is on e-85 and not stock . i cleaned the entire fuel system 2 times fresh good gas in it, pulled the injectors soaked cleaned used a battery to cycle them. i gave up for awhile then i finally listened to myself and my buddy's, sent the injectors to be cleaned by an actual machine. worked like a charm. cleaning them with a battery s good but it really doesn't clean them like a machine. even though they are stock and you are running pump gas if the car has sat for a while it might just be worth the $50 or so to clean them. i plan on pulling mine again once i get ready to pull it out for the year and send them to get cleaned. local guy does it for $40 so not even worth the frustration. might be worth looking into though. Good Luck!!

 

[Crackerman]

I wouldn't forego the possibility of a chip in the ecm. If that's the case, a clutch switch would still affect it.

Unless quickduc has verified it for sure.

 

[pauleyman]

I wouldn't forego the possibility of a chip in the ecm. If that's the case, a clutch switch would still affect it.

Unless quickduc has verified it for sure.

This is a good point. If it's a clutch switch related issue you could verify it easily and rule out load. Simply run the car slowly in first gear all the way to 5500. If it still cuts out it isn't load related. You don't have to run the car hard just ease up the RPM range

 

[Crackerman]

Unplugging the switch would give it a false "pedal is stepped in".

This is why I like to use my cruise switch as a clutch cut...

 

[quickduc]

Wastegate appears to be closed. Moves freely when the rod is disconnected, and reconnects without preload. Still need to get the compressor fired up to check the wastegate pot. No obvious cracks in the turbo housing. It's making boost, as it pulls hard when I put my foot in it. I know what it feels like when it has gasahol in it, and I had a '91 2L N/A, so I'm confident in saying that.

Had to work on some jobs, that, along with heavy rains and high winds have kept me from doing any more on it for a few days. More rain heading in tomorrow, so will probably be a few more days before I can continue checking the other items suggested.

 

[gdb1039]

I had a similar issue with a previous 95 gst and found the cams jumped a tooth throwing the cam position sensor off. Would rev fine up to around 5k just fine but after that it would start to miss fire and not rev any higher.

 

[quickduc]

I'm pretty sure the cam belt is set correctly. I've replaced it at least 3 times by now. Always acted the same. Bit fanatical about gear alignment for this.

I change the belt about every 30k miles. A sister had an identical Talon that broke that belt every 40k. That may not be common, but I'd rather err on changing it too soon than too late. The dealer destroyed her engine on the third belt change, and then told her that there was a junkyard down the road that would give her $50 for the car. 7 year old Talon AWD/leather interior with 100k miles. They were planning on trading it in after a trip down the coast to see the M-i-L.

She gave it to dad, who towed it to the other coast, and told his buddy about it, as he was looking for a replacement engine. His buddy was a district rep for Mitsubishi. He wanted to look at the car. Seems that the dealer's mechanic ignored a TSB that required the oil pump pulley nut be removed and Loctited whenever that belt was changed. It came loose 100 miles down the road.
That was an expensive decision by the dealer to tell my sister to take a hike. I was told that everyone involved was blackballed at Mitsubishi and Chrysler. I think they also paid for the replacement engine.

 

[ist dwa]

My guess is the stock intake pipe is collapsing under boost. That 30 year old POS rubber accordion looking thing is super old and weak by now. It was a common problem among OEM 1G cars but since everybody has mostly replaced that with a hard pipe the issue is deleted/resolved. Cheapest easiest fix is to literally take a worm clamp and put it in the middle of the pipe and make is snug, this will help keep the pipe from distorting, or you could simply buy an aftermarket metal air filter to turbo intake pipe.

This specific issue I am talking about happens at WOT under boost, it starts off fine but as the REVS climb its starts getting chocked and boost plummets where it feels like you need to shift as air flow has literally been chocked off. Since you don't have a boost gauge you can't confirm this but to you it just feels as if the engine has slowed reving and it has.

Hope this helps.

 

[quickduc]

I'll check as soon as it quits raining kittens and puppies. I might have one with my spare motor, need to check both.

 

[quickduc]

"My guess is the stock intake pipe is collapsing under boost."

BINGO!!!

Installed a hose clamp as suggested, and the problem mostly disappeared. Slow rev no problem. Stomp on it, and you can feel it starting to fade a bit as it passes 6500rpm.

Thank you , ist dwa!

 

[o0GuitarKid0o]

Replaced the fuel pump when it started stalling below a 1/4 tank. Put in a Walbro 255
.

Did you just install the 255 with out a Adjustable fuel pressure regulator? Only asking because you'll over run the stock fpr with a 255 .
With 195's you can get away with the stock pressure regulator .

Glad you sorted out the issue though that would be a fun one to try and figure out

 

[quickduc]

I quoted the wrong size. It was the smaller pump that they make. Don't know why 255 popped into my mind.

I'm thinking you would need a dyno to run it on to see the hose distort under operating conditions.

Glad the car transporter decided to park his rig on the cross street. While he was strapping the Talon down for it's trip to TX, a drunk girl came up my street in an SUV and bounced off a roommates car and slammed head-on into a tree. Her front wheels wouldn't rotate or turn, but she was determined to get it moving. Good thing it wouldn't, or she would have backed into another of our cars. She was burning rubber, and got it off the curb, but finally gave up. The car she hit was also totaled, and the tree isn't looking too healthy, either.

 

[1990TSIAWDTALON]

DSM Gods were looking after you!

 

[SouthIndy_Talon]

Are there any readily available intake pipes that would simply be a direct swap for the accordion looking piece?... one that would allow for the use of the stock airbox and MAF as well as not needing the weird 4" - 2.25" adapter on the turbo inlet? Basically a stock replacement piece?

Or does someone have the fab skills to do so......

 

[1990TSIAWDTALON]

Dejon tool used to make them.

 

[SouthIndy_Talon]

I assume this really isn’t an option anymore unless it you are able to find one in the used market? Haven’t heard or seen anything from them in a long time. I would definitely be interested in something like this.

 

[1990TSIAWDTALON]

Keep your eyes on the classifieds on here. I have seen a few come up.
Your situation made me think about a kid in my town that has a '90 GSX that was bone stock. He was doing "something" to it, then got ahold of me to see if I could figure out why it would fall on its face as boost tried to come in. I found a red rag stuffed into the turbo that he had completely forgot about. It sure helped when I got that thing out, .

 

[SouthIndy_Talon]

Yeah... the car will go past 5500, but it just seems to start to struggle the higher you try to go. The throttle body probably needs rebuilt, but I could see a collapsing intake tube almost having the same effect. My car is still stock (minus exhaust) so it still has that original intake tube.