1 2
Sonic
Sonic UberDork
9/28/22 8:41 p.m.

I left today to transit to the start of the Lemons New England rally, which starts Friday morning.  On the 400 mile drive from PA to my family's house in MA my 84 Corvette Ran great for the first 250.  Then it started doing a thing where with heavier throttle it would just stop accelerating.  The amount of throttle needed to make it cut out gradually decreased with time to the point it was throttle barely cracked open, and more and it would lose speed.   
 

Stopped for 5 minutes, gave it a once over and did t see anything wrong, but wiggled the TPS connector as the locking tang has been broken off.  Car then ran great for about 40-50 miles when it did it again, gradually getting worse.  So, I stopped again and did the same thing, and got another 40 miles til it started and then nursed it another 15 and did the same thing which got me to the house.   
 

I have done a tremendous amount of work to this car in the last 1.5 years but driven it little.  Recently did a 200 mile round trip in addition to the usual trips to work and all was well, this is new today.  Fuel filter is new and within 1k miles I have literally wiped the tank clean.  All tune up stuff is basically new.  
 

I’m thinking TPS or ignition coil, any other ideas for those more familiar with old GM cars than I am?  I need to fix this tomorrow for the rally start.   

daytonaer
daytonaer HalfDork
9/28/22 8:45 p.m.

Fuel pump?

Slippery
Slippery GRM+ Memberand PowerDork
9/28/22 9:02 p.m.

I had a problem just like that on my w126 Mercedes and it ended up being the fuel pump. I would shut it off, restart and it would run for another 50 miles or so. 

Not saying its your problem, but I would check the fuel pump's amp draw to rule it out. 

Sonic
Sonic UberDork
9/28/22 9:05 p.m.

Fuel pump is new.  Good tip on trying to check the amps, I'll see if I can get an ammeter, I'm not at home so tools are limited unfortunately 

APEowner
APEowner GRM+ Memberand UltraDork
9/28/22 9:35 p.m.

My first guess is fuel pump.  Net time it dies see if you have spark and if you can check fuel pressure.

Sonic
Sonic UberDork
9/28/22 9:58 p.m.

I loaded up the parts cannon as AutoZone can deliver it all to me tomorrow.  TPS, ignition coil, ignition module, and fuel pump.  I can return whatever I don't need.  

David S. Wallens
David S. Wallens Editorial Director
9/28/22 10:04 p.m.

Fuel filter? 

californiamilleghia
californiamilleghia UltraDork
9/28/22 10:04 p.m.

Fuel filter......maybe it mostly clogged and after 50 miles pushes enough sediment that  it totally clogs,.....

it happened to my Chevy van once and max speed was 50mph.....

cdowd (Forum Supporter)
cdowd (Forum Supporter) Dork
9/28/22 10:05 p.m.

Check fuel filter also.  May still flow but not high enough rate.

Sonic
Sonic UberDork
9/28/22 10:11 p.m.

Highly doubt it is the fuel filter as less than 1k miles ago I had the tank open and literally wiped it clean, it is lined with some kind of rubber and it was spotless.  I replaced the fuel pickup, filler/sender, and the filter at the same time.  

dclafleur
dclafleur Reader
9/28/22 10:20 p.m.

Which fuel pump? My '85 struggled with this too. It was a fuel pump issue. The pump is cooled by the gas, as the gas in the tank heats up/level drops the pump loses efficiency. This is compounded with the older style pumps with ethanol blended gas which has a lower specific heat capacity. Higher fuel temperature with the pressure drop at the fuel pump inlet causes cavitation which causes greater heat in the fuel pump leading to more cavitation and heat build up. The answer for me was to swap out a newer style fuel pump the specifically stated it could handle ethanol, I went through two OE style pumps in short order before finding one that worked for longer, it has worked long enough that I can't find my records on which pump I ended up with.

Sonic
Sonic UberDork
9/28/22 10:39 p.m.

Fuel pump in there now is a stock replacement from Delphi.  This started happening today with more than a half tank, down to about 1/4.   I'll try the other parts first before I open up the tank again for the pump, but good to hear your experience, thanks, glad I added the pump to my order.   

Nockenwelle
Nockenwelle New Reader
9/28/22 11:44 p.m.

Sounds silly but check to make sure the fuel tank venting is working properly, including the fuel cap. I've seen cases where it isn't, and the pump reaches a point after some run time when it can no longer pull fuel thru the pickup against tank vacuum. This is exacerbated by the unfortunate truth that most new electric in-tank pumps aren't as good as the ones they replace. Your shutdown time may be enough for the negative pressure to bleed off thru any remaining but restricted venting. EVAP malfunction may contribute to this nonsense.

Check the fuel pressure at the rail when it's having issues. 

eastsideTim
eastsideTim UltimaDork
9/29/22 9:37 a.m.

One more thing regarding the fuel pump - GM wiring for the pump tends to be marginal when new, and gets worse as it ages.  I suspect that is why they have a reputation for crappy replacement pumps that don't last long.  If it is not too difficult, you may want to rerun the wiring for the pump with some thicker wire.

Toyman!
Toyman! GRM+ Memberand MegaDork
9/29/22 9:42 a.m.

Loosen the gas cap. Sounds like it's drawing a vacuum on the fuel tank. 

stuart in mn
stuart in mn MegaDork
9/29/22 9:52 a.m.
Nockenwelle said:

Sounds silly but check to make sure the fuel tank venting is working properly, including the fuel cap. I've seen cases where it isn't, and the pump reaches a point after some run time when it can no longer pull fuel thru the pickup against tank vacuum.

What I was going to say, it's happened to me before.  Next time it happens, open the fuel cap and see if you hear air rushing in.

06HHR (Forum Supporter)
06HHR (Forum Supporter) Dork
9/29/22 10:09 a.m.

In reply to Sonic :

My money is on the ignition module, they get hot and crap out.  Then work wonderfully once they cool off a bit. A few miles down the road, rinse and repeat.  I'd do the ignition bits first, starting with that one. 

Paul_VR6 (Forum Supporter)
Paul_VR6 (Forum Supporter) UltraDork
9/29/22 10:20 a.m.
Toyman! said:

Loosen the gas cap. Sounds like it's drawing a vacuum on the fuel tank. 

Had this happen a few times with various cars, vent was plugged or line to evap was pinched. Also seen old fuel pump relays with bad contacts do this once they got hot.

parker
parker HalfDork
9/29/22 11:38 a.m.
06HHR (Forum Supporter) said:

In reply to Sonic :

My money is on the ignition module, they get hot and crap out.  Then work wonderfully once they cool off a bit. A few miles down the road, rinse and repeat.  I'd do the ignition bits first, starting with that one. 

Yes, I had this happen on an MG and a 911.  

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) GRM+ Memberand UltraDork
9/29/22 12:58 p.m.

Had this happen in early EFI mustangs.  Ignition modules, fuel filters and clogged fuel socks on the pickup were the usual culprits.

bobzilla
bobzilla MegaDork
9/29/22 1:52 p.m.

Most of the time I saw this on small cap HEI and the ignition module would overheat and shut down. Lot of people changed the fuel pumps because they also triggered the pump IIRC. 

Toyman!
Toyman! GRM+ Memberand MegaDork
9/29/22 1:55 p.m.

The reason I don't think it's the ignition module is they were usually on or off. They didn't gradually get worse. They just quit. 

 

parker
parker HalfDork
9/29/22 4:01 p.m.
Toyman! said:

The reason I don't think it's the ignition module is they were usually on or off. They didn't gradually get worse. They just quit. 

 

That's what I was told with my 911.  Turns out "they" were wrong.

paul_s0
paul_s0 Reader
9/29/22 4:28 p.m.
parker said:
06HHR (Forum Supporter) said:

In reply to Sonic :

My money is on the ignition module, they get hot and crap out.  Then work wonderfully once they cool off a bit. A few miles down the road, rinse and repeat.  I'd do the ignition bits first, starting with that one. 

Yes, I had this happen on an MG and a 911.  

I also had it happen, on a Peugeot 309 GTi..

bobzilla
bobzilla MegaDork
9/29/22 4:40 p.m.
paul_s0 said:
parker said:
06HHR (Forum Supporter) said:

In reply to Sonic :

My money is on the ignition module, they get hot and crap out.  Then work wonderfully once they cool off a bit. A few miles down the road, rinse and repeat.  I'd do the ignition bits first, starting with that one. 

Yes, I had this happen on an MG and a 911.  

I also had it happen, on a Peugeot 309 GTi..

Ford Tempos and Topaz's would do the same thing. 

1 2
Our Preferred Partners
HF5QLKZrvAb3rdkPqvgV3wAnnV3SFgdK7WRIiQGpe5FOxTqeblgchI0F8M5V8x94