Pennock's Fiero Forum
  Technical Discussion & Questions
  GT Won't go over 3000rpm While Driving

Post New Topic  Post A Reply
Email This Page to Someone! | Printable Version


next newest topic | next oldest topic
GT Won't go over 3000rpm While Driving by reinhart
Started on: 06-06-2021 07:33 PM
Replies: 17 (213 views)
Last post by: zkhennings on 06-11-2021 12:43 PM
reinhart
Member
Posts: 658
From: Orange County, CA
Registered: Mar 2002


Feedback score: N/A
Leave feedback

Rate this member

Report this Post06-06-2021 07:33 PM Click Here to See the Profile for reinhartClick Here to Email reinhartSend a Private Message to reinhartEdit/Delete MessageReply w/QuoteDirect Link to This Post
88 GT 5 speed:

This problem just came on all of a sudden. It didn't gradually get worse over time.

In neutral I can rev the engine to redline normally but when I'm driving I can't get over 3000rpm regardless of gear. It pulls normally up to 3000 and then it tops out. I push the accellerator down further and it makes absolutely no difference. It doesn't backfire or surge or anything just won't rev any higher.

I have a test pipe in place of the cat.
No trouble codes.

I tried replacing the ignition coil with a new one and no difference. I noticed one of the wires to the ignition coil had a slight tear in the insulation and was exposed, and I taped it up in case that was causing a short to ground.

Plugs and wires cap and rotor are pretty new.

Anyone have a similar problem and what was the remedy?

[This message has been edited by reinhart (edited 06-06-2021).]

IP: Logged
PFF
System Bot
Mike in Sydney
Member
Posts: 374
From: Meadow Flat, NSW, Australia
Registered: Sep 2011


Feedback score: N/A
Leave feedback

Rate this member

Report this Post06-06-2021 08:06 PM Click Here to See the Profile for Mike in SydneySend a Private Message to Mike in SydneyEdit/Delete MessageReply w/QuoteDirect Link to This Post
Check your fuel filter. On my Holden Jackaroo (Isuzu Trooper) 4x4, I was losing power going up hills on the highway. No codes on the box and the car would rev normally in the driveway. I described the issue to my mechanic friend who's the techinspector for our car club (Bathurst Feral Utes Cars and Trucks (BFUCT)) and he said "fuel filter". I changed the filter and the problem went away.

If it's not the fuel filter it could be a fuel pressure issue but I expect the two are linked with a blocked filter causing low fuel pressure.

Just my 2-cents worth.
IP: Logged
reinhart
Member
Posts: 658
From: Orange County, CA
Registered: Mar 2002


Feedback score: N/A
Leave feedback

Rate this member

Report this Post06-06-2021 08:10 PM Click Here to See the Profile for reinhartClick Here to Email reinhartSend a Private Message to reinhartEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Mike in Sydney:

Check your fuel filter. On my Holden Jackaroo (Isuzu Trooper) 4x4, I was losing power going up hills on the highway. No codes on the box and the car would rev normally in the driveway. I described the issue to my mechanic friend who's the techinspector for our car club (Bathurst Feral Utes Cars and Trucks (BFUCT)) and he said "fuel filter". I changed the filter and the problem went away.

If it's not the fuel filter it could be a fuel pressure issue but I expect the two are linked with a blocked filter causing low fuel pressure.

Just my 2-cents worth.


Fuel filter has about 5000 miles on it so I don't think that would be it. If it revs fine in neutral does that eliminate the fuel as a potential issue? In other words does it use relatively the same amount of fuel at 6000 rpm in neutral as it does at 6000 rpm in 2nd gear?

[This message has been edited by reinhart (edited 06-06-2021).]

IP: Logged
Spoon
Member
Posts: 3493
From: Sadsburyville, PA. 19369 / USA
Registered: May 2004


Feedback score:    (16)
Leave feedback





Total ratings: 60
Rate this member

Report this Post06-06-2021 08:58 PM Click Here to See the Profile for SpoonSend a Private Message to SpoonEdit/Delete MessageReply w/QuoteDirect Link to This Post
It uses more fuel under load at same rpm. Also 5000 miles on filter with crap fuel is not same as 5000 with good quality fuel.

Just my 2 cents.

Spoon

------------------
"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut

IP: Logged
reinhart
Member
Posts: 658
From: Orange County, CA
Registered: Mar 2002


Feedback score: N/A
Leave feedback

Rate this member

Report this Post06-06-2021 09:23 PM Click Here to See the Profile for reinhartClick Here to Email reinhartSend a Private Message to reinhartEdit/Delete MessageReply w/QuoteDirect Link to This Post
Just ran a pressure test following the service manual at the shraeder valve. It passed. 44psi key on and 38psi at idle. Revving it fluctuates between 36--39.

Now, I'm assuming it must be electrical unless I'm missing something,
IP: Logged
Mike in Sydney
Member
Posts: 374
From: Meadow Flat, NSW, Australia
Registered: Sep 2011


Feedback score: N/A
Leave feedback

Rate this member

Report this Post06-07-2021 12:00 AM Click Here to See the Profile for Mike in SydneySend a Private Message to Mike in SydneyEdit/Delete MessageReply w/QuoteDirect Link to This Post
Don't think it's likely to be anything electrical if you aren't getting misfiring when you rev it at rest. Although, I guess you could have problems with the sparkplug wires.

Out of curiosity, have you looked at the fuel filter since you changed it? If you have a rusty tank, there is a strong possibility that you've a obstructed filter. My suggestion: Spend the $10 or so for a new filter and replace it. Open the old filter and see if you have rust in the filter media.

CAUTION: MANUALLY open the old filter in an open, well ventilated environment away from electrical appliances, angle grinders, cutting torches, open flames, cigarettes, cigars, doobies, etc. Have you wife, buddy, or someone close by with a fire extinguisher, fire blanket, fire hose, fire-fighting foam generating machine, etc. in case you set yourself on fire. Wear goggles, nomex hood and gloves, and a nomex firesuit, for added protection.

(BTW, Let us know what the issue is when you solve it.)

[This message has been edited by Mike in Sydney (edited 06-07-2021).]

IP: Logged
Dennis LaGrua
Member
Posts: 14159
From: Hillsborough, NJ U.S.A.
Registered: May 2000


Feedback score:    (13)
Leave feedback





Total ratings: 323
Rate this member

Report this Post06-07-2021 10:49 AM Click Here to See the Profile for Dennis LaGruaClick Here to Email Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
Sure sounds like an obstruction in the fuel system somewhere, a bad fuel pump or a rotted connection from the fuel pump to the outlet tube. Many times people use std fuel injection hose to make that connection. Over time it enlarges and breaks. You must use J30R10 submersible fuel hose there, or the pulsator that you no longer need with todays turbine fuel pumps that put out constant pressure.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

IP: Logged
reinhart
Member
Posts: 658
From: Orange County, CA
Registered: Mar 2002


Feedback score: N/A
Leave feedback

Rate this member

Report this Post06-08-2021 05:46 AM Click Here to See the Profile for reinhartClick Here to Email reinhartSend a Private Message to reinhartEdit/Delete MessageReply w/QuoteDirect Link to This Post
wouldn't a fuel pressure test detmonstrate whether there's an obstruction (leak) in the fuel lines? I mean shouldn't it fail the pressure test (drop below the minimum level)? If I can rev it to redline while parked without the fuel pressure dropping, how can the fuel filter or lines be a problem? Also how would a clogged fuel filter be perfect one day and not allow it to rev over 3000 under load the next day? Fuel filters shouldn't be binary like that. I'm not necessarily opposed to changing it but it just seems like it's not a likely culprit.

If it were electrical, is the consensus that there would be unburnt fuel in the exhaust which would cause a backfire? I haven't gotten a single backdire. I can literally floor it and if anything, the car and revs slow ever so slightly if I get past a certain point on the throttle.

[This message has been edited by reinhart (edited 06-08-2021).]

IP: Logged
reinhart
Member
Posts: 658
From: Orange County, CA
Registered: Mar 2002


Feedback score: N/A
Leave feedback

Rate this member

Report this Post06-08-2021 05:58 AM Click Here to See the Profile for reinhartClick Here to Email reinhartSend a Private Message to reinhartEdit/Delete MessageReply w/QuoteDirect Link to This Post
Dennis regarding the fuel pump, I changed the original GM pump about 30,000 miles ago. I used a Delco brand. I don't believe there are any rubber lines inside the tank. I did replace the strainer of course but reused everything else.

[This message has been edited by reinhart (edited 06-08-2021).]

IP: Logged
zkhennings
Member
Posts: 1572
From: Massachusetts, USA
Registered: Oct 2010


Feedback score: (3)
Leave feedback

Rate this member

Report this Post06-08-2021 02:31 PM Click Here to See the Profile for zkhenningsSend a Private Message to zkhenningsEdit/Delete MessageReply w/QuoteDirect Link to This Post
Fuel and air are you factors that will differ when parked vs when driving. The car will consume much more fuel and air under load, spark however is the same. If it can rev out at idle then spark is almost certainly not the issue.

I would agree that it is probably a restriction to the fuel. You really need to record the fuel pressure while driving to be certain it is not a fuel issue. You can have good pressure when parked and the engine is not asking for a lot of fuel, but poor pressure when the fuel demand goes up when driving. Could you mount the gauge and have a go pro record it?

It could also be air, if you have a massive restriction in your air intake system. Pushing air out could also be a restriction, you make a lot more exhaust under load than when parked.
IP: Logged
Patrick
Member
Posts: 31580
From: Vancouver, British Columbia, Canada
Registered: Apr 99


Feedback score: (1)
Leave feedback





Total ratings: 446
Rate this member

Report this Post06-08-2021 02:45 PM Click Here to See the Profile for PatrickClick Here to Email PatrickSend a Private Message to PatrickEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by reinhart:

I changed the original GM pump about 30,000 miles ago... I don't believe there are any rubber lines inside the tank.


Ummm...




Another possibility is that your muffler is partially blocked with broken up innards from the removed cat.
IP: Logged
PFF
System Bot
zkhennings
Member
Posts: 1572
From: Massachusetts, USA
Registered: Oct 2010


Feedback score: (3)
Leave feedback

Rate this member

Report this Post06-08-2021 03:13 PM Click Here to See the Profile for zkhenningsSend a Private Message to zkhenningsEdit/Delete MessageReply w/QuoteDirect Link to This Post
As someone who has had the hose inside the tank split (reused the 4cyl submersible hose in a V6 swap), it will not develop full fuel pressure during priming, idling, or driving, so while a possible point of failure for the fuel system, I would be surprised if it is the culprit here.
IP: Logged
reinhart
Member
Posts: 658
From: Orange County, CA
Registered: Mar 2002


Feedback score: N/A
Leave feedback

Rate this member

Report this Post06-08-2021 04:44 PM Click Here to See the Profile for reinhartClick Here to Email reinhartSend a Private Message to reinhartEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by zkhennings:

Fuel and air are you factors that will differ when parked vs when driving. The car will consume much more fuel and air under load, spark however is the same. If it can rev out at idle then spark is almost certainly not the issue.

I would agree that it is probably a restriction to the fuel. You really need to record the fuel pressure while driving to be certain it is not a fuel issue. You can have good pressure when parked and the engine is not asking for a lot of fuel, but poor pressure when the fuel demand goes up when driving. Could you mount the gauge and have a go pro record it?

It could also be air, if you have a massive restriction in your air intake system. Pushing air out could also be a restriction, you make a lot more exhaust under load than when parked.


Interesting idea. I was trying to rack my brain as to how I could be able to see the guage while driving when I was testing it in the driveway. I don't have a go pro but it gives me the idea to use a cell phone video recorder. I could tape both the gauge and phone in place. and just have it record for a couple minutes while I drive around. I'll have some time to work on this later in the week. Thanks for the ideas guys.
IP: Logged
reinhart
Member
Posts: 658
From: Orange County, CA
Registered: Mar 2002


Feedback score: N/A
Leave feedback

Rate this member

Report this Post06-08-2021 04:47 PM Click Here to See the Profile for reinhartClick Here to Email reinhartSend a Private Message to reinhartEdit/Delete MessageReply w/QuoteDirect Link to This Post

reinhart

658 posts
Member since Mar 2002
 
quote
Originally posted by Patrick:

Ummm...




Another possibility is that your muffler is partially blocked with broken up innards from the removed cat.


Ah there is one rubber connector. I reused that.

Regarding the cat, It was removed about 25 years ago lol.

[This message has been edited by reinhart (edited 06-08-2021).]

IP: Logged
Dennis LaGrua
Member
Posts: 14159
From: Hillsborough, NJ U.S.A.
Registered: May 2000


Feedback score:    (13)
Leave feedback





Total ratings: 323
Rate this member

Report this Post06-08-2021 05:34 PM Click Here to See the Profile for Dennis LaGruaClick Here to Email Dennis LaGruaSend a Private Message to Dennis LaGruaEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by reinhart:


Ah there is one rubber connector. I reused that.




I would guess that there is a small leak in that old connector hose limiting the supply at high engine demand. You can buy or borrow (many auto stores loan them out) a fuel pressure gauge with a 3' hose. Attach the gauge to the schrader valve on the fuel rail , remove the passenger side vent grill and tape the gauge to the rear window. Accelerate to the 3000 rpm limit and have an assistant record the readings. If you do not get about a 43 psi reading then it is the hose connection, the fuel pump or possibly a bad connection at the connector near the firewall.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

IP: Logged
reinhart
Member
Posts: 658
From: Orange County, CA
Registered: Mar 2002


Feedback score: N/A
Leave feedback

Rate this member

Report this Post06-09-2021 05:35 PM Click Here to See the Profile for reinhartClick Here to Email reinhartSend a Private Message to reinhartEdit/Delete MessageReply w/QuoteDirect Link to This Post
I own a gauge like that which is what I used to test it. I'll likely get a chance to test it on the road tomorrow. I'll report back.
IP: Logged
reinhart
Member
Posts: 658
From: Orange County, CA
Registered: Mar 2002


Feedback score: N/A
Leave feedback

Rate this member

Report this Post06-11-2021 12:45 AM Click Here to See the Profile for reinhartClick Here to Email reinhartSend a Private Message to reinhartEdit/Delete MessageReply w/QuoteDirect Link to This Post
I hooked up the fuel pressure gauge and taped my cell phone nearby and went out for a drive. The car was back to its old self. No issues revving and power was great. LOL So the only thing I messed with since my previous last test drive was some of the wires that go from the distributor to the ignition coil I had repositioned and reinsulated a few days ago but never took it out for a test driv. I mentioned one wire had a fray previously although I had taped it up and my test drive after that didn't make a difference.

So either the problem is intermitant or it was the wires from the distributor to the ignition coil. Regardless fuel supply block/leak ideas were incorrect. It could also be some other intermittant spark issue.

Thanks for the ideas. I'll update if the gremlin comes back.
IP: Logged
zkhennings
Member
Posts: 1572
From: Massachusetts, USA
Registered: Oct 2010


Feedback score: (3)
Leave feedback

Rate this member

Report this Post06-11-2021 12:43 PM Click Here to See the Profile for zkhenningsSend a Private Message to zkhenningsEdit/Delete MessageReply w/QuoteDirect Link to This Post
I very much doubt it was an issue with driving vs parked then, and more of an intermittency that got triggered when you were driving by luck (or unluck). Those cables that go to the ignition coils and distributer are suspect and should be replaced IMO, they are right above the exhaust and I have seen them become an issue on my Fiero and others. Though usually they cause the car to intermittently die and not have a rev limiting effect. You can construct new ones yourself from connectors with pigtails that you can buy from RockAuto. I soldered and heatshrinked mine together but crimps would work fine too.
IP: Logged

next newest topic | next oldest topic

All times are ET (US)

Post New Topic  Post A Reply
Hop to:

Contact Us | Back To Main Page

Advertizing on PFF | Fiero Parts Vendors
PFF Merchandise | Fiero Gallery | Ogre's Cave
Real-Time Chat | Fiero Related Auctions on eBay



Copyright (c) 1999, C. Pennock