Still cant rev past 3500rpm

[sixt9coug]

After trying to work with my new 94 GT lately I still cant seem to track down why it won't rev past 3500 rpm. It still has somewhat of a rough idle too.

The coil was bad so we replaced that. New plug wires at the same time. We didn't change the plugs yet but i did buy some (too lazy). We put a new fuel filter on it as well with no change.

I cleaned the MAF, to no change. We disconnected the MAF and drove it. The idle smoothed out a bit but when driving it there was still the same problem.

In the other thread before i bought it, someone mentioned the PIP? That is an internal distributor part right? How would I test that without swapping it out for another part (I don't have a spare distributor handy). Anyone have any other ideas of what it could be and how to test the part? There is no CEL on either.

The car pulls pretty strong otherwise. Just when it gets around 3000-3500 rpm it just acts like its hitting a rev limiter.

TIA.

 

[HankyGT]

Check the timing. Make sure the spout connector is in place by the MAF harness. Check for correct fuel pressure. Check plug gap (use new clean plugs). Could be the PIP but you can at least check the rest before spending coin on a dizzy.

 

[Dino Dino Bambino]

I've heard of many cases of such a problem being caused by plugged up cats. Might be worth checking them out.

 

[Hef5.0weisen]

sounds like mighty PIP sensor is showing its ugly face again...mine was doing the same thing, acting like a rev limiter ~3500.

Some say to pull the cap off and look for excessicve dust, I did, nothing abnormal. I don't know of a way to check it, but I'll offer this:

Go to the parts store and get another one,(~80 bucks for a re-man dizzy, PIP SHOULD have been replaced) with a warranty, swap em out, see what happens. If it still does it, get another...and I say that based on another memebers bad experience with replacement distributors/PIP sensors.
Pro's; you win some you lose some, shotgunning parts can get pricey, but with a warranty you shouldn't lose any money, maybe you'll win first time..
Con's: just that, shotgunning parts, maybe someone else knows a way to test a PIP, but swapping it(the whole distributor) may be just as easy...

Replacing the PIP(~20 bucks) is easy if you want to go that route, but tools may be an issue. You'll need a 5.5mm socket to get the PIP out, and should use a press to get the gear off the dizzy shaft. A good bench vise and a heavy mallet works, but is not a desireable method. There should be a thread about the process if you search for it, again easy to do, but those arent't the most common tools.

Also, be prepared to get a new balancer, I say this as a precaution. If yours is original, chance's are it is spun, what you see with a timing light may not be accurate. It'll be a pain in the bootie trying to time it, I'd just get a new one, they're not to bad on the wallet, and I imagine you could borrow the puller form one of the parts stores (I own one, the puller that is).

good luck, wish you success...let us know if you need any more info

-Brian

 

[sade04]

maybe a long shot but check to see if your plugs are correctly gapped. When i got my car they were gapped too wide and the car would fall flat on its face at 4000rpm

 

[90lxcoupe]

I'd also bet its the PIP, my car had that issue a few years ago, in my case the car would run fine for 10-15 minutes then when the PIP got hot it would do exactly what your saying.

 

[HISSIN50]

Pull codes even if the CEL isn't on.

Do you have a spare MAF?

The TFI is another thing to check. When they start to go, they can act like a rev limiter at around 4K RPM.

Be sure you dont have platinum plugs in there now. They can show you a weak ignition by acting like a limiter and causing a low and rough idle.

Good luck.

 

[sixt9coug]

sounds like mighty PIP sensor is showing its ugly face again...mine was doing the same thing, acting like a rev limiter ~3500.

Some say to pull the cap off and look for excessicve dust, I did, nothing abnormal. I don't know of a way to check it, but I'll offer this:

Go to the parts store and get another one,(~80 bucks for a re-man dizzy, PIP SHOULD have been replaced) with a warranty, swap em out, see what happens. If it still does it, get another...and I say that based on another memebers bad experience with replacement distributors/PIP sensors.
Pro's; you win some you lose some, shotgunning parts can get pricey, but with a warranty you shouldn't lose any money, maybe you'll win first time..
Con's: just that, shotgunning parts, maybe someone else knows a way to test a PIP, but swapping it(the whole distributor) may be just as easy...

Replacing the PIP(~20 bucks) is easy if you want to go that route, but tools may be an issue. You'll need a 5.5mm socket to get the PIP out, and should use a press to get the gear off the dizzy shaft. A good bench vise and a heavy mallet works, but is not a desireable method. There should be a thread about the process if you search for it, again easy to do, but those arent't the most common tools.

Also, be prepared to get a new balancer, I say this as a precaution. If yours is original, chance's are it is spun, what you see with a timing light may not be accurate. It'll be a pain in the bootie trying to time it, I'd just get a new one, they're not to bad on the wallet, and I imagine you could borrow the puller form one of the parts stores (I own one, the puller that is).

good luck, wish you success...let us know if you need any more info

-Brian

Good info, I was messing with it again today and still made no progress. I felt around the balancer for rubber sticking out or anything and there wasn't anything abnormal. It felt smooth all the way around. Yeah I know that isn't the most scientific way to test it, but reading other posts from guys here said that they had crap sticking out so it was worth a shot. I will probably buy a distributor and I'll try go con a friend into swapping it out while I'm out of town next week.

I was reading about the dizzy on Napa and Autozone's website and they said the dizzy doesn't come with the module. Should I replace that at the same time?

Pull codes even if the CEL isn't on.

Do you have a spare MAF?

The TFI is another thing to check. When they start to go, they can act like a rev limiter at around 4K RPM.

Be sure you dont have platinum plugs in there now. They can show you a weak ignition by acting like a limiter and causing a low and rough idle.

Good luck.

TFI? I'm used to carburators and ignition points, what's the TFI? No spare MAF to check, but when we unplugged the MAF and drove it, nothing changed. No MAF and the same problem so will that rule it out? Or is there more to it?

Like I said, I'm not too EFI savvy.

 

[HISSIN50]

If you unplug the MAF and nothing changes, that can suggest the MAF isn't functioning properly (if it was functioning properly and you unplugged it, something should change, right?). It's probably not the MAF but if you had a spare, it'd be nice to try to rule it out.

The TFI is the ignition module.

 

[Hef5.0weisen]

A bit on part store dizzy's for you;

If you get one it may look differnt. They may sell you a Fox type dizzy. Fit and function are the same, however the Fox type has a mount pad for the TFI module while ours are remote mounted (TFI module)under the air filter. Fugly, but you'll be rolling again if that is the case, mere aesthetics, important thing is to be able to tack it out to 5800 and melt the tires right??

FWIW, I have the Fox type on mine now, works fine. I replaced the PIP in the original, installed, ops checked, and removed, put the new one back in. Little extra work, but now I have a ready spare. It lives in my trunk waiting to be released on one of those cold rainy nights broke down on some middle of nowhere highway, with grizzly bears chasing you. Those things crap out, you're hosed..besides, who wants to be eaten by grizzly bears??

Intent is to save you the headache when (if) you look at a new one and think "What did the cat sell me?" And as you well know, if it goes out, you may be walking home, worst case is aliens are chasing you, trying to do experiments....not a bad idea to keep a spare to get out of Dodge, especailly if your adventures take you far from home...and no one wants to get probed by aliens!!!

Bit of a tangent there, I know, but its late and I've been up for 32 hours now, need some rest...

Hope you get it!
-Brian

and the balancer, well when I went thru this ordeal (no aliens or grizzlies thankfully) I was getting beat up trying to get the timing right. Didn't have the tell tale sign of the rubber hanging out=bad balancer. Assumed it was good to go...WRONG. Got back to basics and found TDC using the spark plug hole/piston..balancer should have been at zero, well, i was at ~30 didn't waste too much time with that, but being on here for a few years and reading balancer stories got me out of that trap. If the grizzlies or aliens were around, I'd be a mangled carcass or have a size 9 poop chute....

 

[sixt9coug]

Loooooooooooooooong road to the promise land but heres an update.

Still bucking and can't get it past a certain rpm. Still a miss at idle and theres a little bucking around 1500rpm. My only real useable rpm range is like 1700-2900ish...

So this is what have done to date since buying the car. My buddy Pete has been great with the troubleshooting and putting up with my stupid questions.

- New fuel filter. no change in anything.
- New ignition coil - same time as the wires
- New plug wires- slightly better idle, no change otherwise.
- Tested a reman MAF no change. sent MAF back
- checked fuel pressure. Seemed ok, but bought a new FPR anyway. no change.
- changed fuel injectors. idles better and smoother, but no change with the rev problem.
- new spark plugs. Car had some platinums in there that did not look like the right plugs. done the same time as the injectors. smoother, but no change with the bucking.


So we started doing more testing. hooked up a Snap On Scanner to it. No codes. confirmed fuel pressure. Seems ok. mid 30s at idle, around 42 with the line off and capped. Fuel flow was tested. Snap On said around 16oz@15 seconds. It handily beat that spec. Snap On tester showed the O2 sensors seemed to be reading pretty steady with each other. The KV were a little higher so my buddy said that meant it was rich. Computer seemed to be adding and pulling fuel as it should.


So we moved to ignition. checked timing. Like i said in another post, we have had issues with this. When pulling the SPOUT and getting the light on it, there are no marks to be seen on the balancer. I naturally thought that meant the balancer had slipped, so we checked it. Nope. it appears to check out when #1 is at about the top of its stroke. The rotor in the dizzy also appears to point at the right cylinder, so it doesn't look like the timing chain jumped anything either. When trying to time it with just the light and the SPOUT out, the problem still occurs. We CANNOT time this thing using traditional methods. We hooked the Snap On scanner up to it, and did what we could to set base timing that way. We drove it and now it pings and still sputters. The idle is a HELL of a lot better though. The computer also was not needing to adjust the fuel as much as it was anymore though.

So we think there is an ignition problem. Does this make sense to anyone? PIP? TFI? ECU problem maybe? I have a T4M0 in the car of course and its stock. The computer seems to be doing fine with the fuel, but i dunno about the spark.

Why does the balancer and all of the actual hard parts check out but when I try to time the car the marks are so far rotated that all I can see are the ATC marks riiiight on the edge of the visible range?

Who has a spare dizzy, TFI and T4M0 sitting around?


Cliff notes
- balancer checks out as not slipped. but when trying to time the car, the marks are sure acting like they are slipped.
- changed lots, think its ignition.

 

[Dino Dino Bambino]

Did you check the cats?

 

[alleymad95GT]

IMHO, the difficulty with the timing makes me lean more towards your PIP / STATOR (same thing - just the parts store prolly has no idea what a PIP is) being bad.

If you wanna dig into how it works, do a Google search for "Hall Effect Sensor." There are lots of different varieties of this mechanism, but basically it is an "on/off" type sensor that triggers all of the rest of the ignition. In our cars, it also interacts with the fuel pump, which is why a lot of the symptoms are similar.

Here's a link for you if you wanna just replace the PIP:

How-To: Rebuild Your Distributor and Replace the Stator

 

[99FiveOh]

Just buy a new dizzy and stab it in there and you'll be good to go. I know you tried this and that.. but the advice in this thread is solid. I'm the one who has been through HELL with dizzies and PIP sensors so I'm somewhat of an expert on what one could expect when they are failing or have failed.

And if you aren't seeing any marks on your balancer then something is really out of whack! Pinging suggests that your timing is too far advanced now. However, a failing PIP will also cause you to have alot of pinging because it too can wreak havoc on your timing. It is directly responsible for relaying exactly where your engine is to the computer, so if it "lies" to your computer your engine will run like crapola!

Change the dizzy, Change the dizzy, CHANGE THE DIZZY NOW!!!! lol

 

[KamiKaziDK]

I think this is a maf problem somehow still. Might want to check all your connections and the resistance through your maf wiring, maybe it's not the sensor...maybe you got a bad rebuild. It's a possibility it's the computer too since that ultimately communicates with the maf. But if you disconnected the maf and absolutely nothing changed, I'd be looking at every thing possible that has to do with it. I had the exact same problem with my car, wouldn't rev over 2800 rpms and ran like total crap, put on a stock maf I had laying around, fixed it.

 

[99FiveOh]

But he tried another MAF other than his with no change. If 2 different MAF's had the same result then it's pretty safe to say it's something else. With all the different opinions going around on this thread this guys head must be spinning! But experience suggest, at least as far as I'm concerned, that his PIP sensor is responsible.

And for the record, every single MAF that I've ever had go bad threw a check engine light, every one. If you unplug the MAF the check engine light will come on as well, it's probably one of the most important sensors in our car.

 

[sixt9coug]

IMHO, the difficulty with the timing makes me lean more towards your PIP / STATOR (same thing - just the parts store prolly has no idea what a PIP is) being bad.

If you wanna dig into how it works, do a Google search for "Hall Effect Sensor." There are lots of different varieties of this mechanism, but basically it is an "on/off" type sensor that triggers all of the rest of the ignition. In our cars, it also interacts with the fuel pump, which is why a lot of the symptoms are similar.

Here's a link for you if you wanna just replace the PIP:

How-To: Rebuild Your Distributor and Replace the Stator

IT'S FIXED!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!


I didn't have time to check this thread today, but just to let you know, this is exactly what it was.

Was it the PIP? I dunno.... but a friend of mine went junkyarding today and he grabbed a T4M0 ECU, a used FoMoCo PIP, TPS sensor and IAC valve (for $35!). We stabbed in the ECU first and it didnt do anything. The old ECU had "Runs But High Idle - 899-3850" written on it with a sharpie. Weird huh?

We then decided to change the PIP. We noticed the Distributor sure looked new. The Hall effect sensor was oddly clean and not pitted, the wiring on the PIP was super new and soft and it all was obviously a reman unit. (not done by me) Well we decided to change it anyway just because i prefer OEM FoMoCo parts in the car instead of the made in china parts. Well, we put the new PIP on and then reassembled the dizzy. What do you think we noticed? rotating it by hand we noticed that the Hall effect sensor was making contact with the pickup! It had a bent fin! DAMN REMAN UNITS!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

We straightened out the fin, stabbed in the dizzy and threw on the OEM TPS and IAC for the hell of it and pulled the SPOUT to set the timing. Well well, RIGHT AWAY we noticed the timing marks were now where they should be. We set it to 10btc and took it for a drive.

It runs like new and pulls all the way now. Damn that was a journey.

 

[sixt9coug]

For the record... my friend that helped me through all this is a Turbo Buick guy. I know there's a little jabbing between the two communities, but he came through when it mattered and took time out from working on his Syclone to get this car back to it's glory.

Thanks Pete!

 

[KamiKaziDK]

Awesome man, good deal. Like I said, all the way back to the computer could be the problem. And FYI Mark, my car never threw a check engine light when my MAF went out on me....it would just idle like butt and not rev past 2800 rmps.

 

[99FiveOh]

Well, I'm glad it's fixed now. It almost makes you wanna get rid of these cars sometimes when you can't figure crap out!

Due to the age of these cars and to a certain degree, mileage (age seems to do them in before mileage) the PIP sensor is now the logical place to start when dealing with symptoms like this. Not only can it cause your car to run like poo, but it can leave you stranded for 30 min to an hour or more! Not a good thing... and if you replace it trying to fix another issue, you'll be ensuring that you're not going to be stranded, regardless if the PIP is the problem or not. They all go bad just like the TFI in the Fox bodies did. I always kept a spare in my 89 and 90 GT's along with a TFI tool.

Unfortunately, A dizzy won't fit in my glove box nor with the vice, hammer, roll pin punch and whatever else is needed for a roadside PIP sensor change! lol

Again, glad you fixed it Pete now you can enjoy your car!