28 replies to this topic

[super B]

My SM race car has an issue with left hand turns, the engine quits on hard left turns for about 4 seconds then picks back up and runs fine.I have been racing the car for five years with no issues other than oil, gas , and brakes. I pulled the fuel pump and found only the filter needed to be changed. no broken baffles in the tank. plenty of gas 1/2 tank.No problems with right turns.I suspect the switch that turns off the fuel pump when and if the car turns upside down..That being said questions are;.Where is is located, what does it look like, can it be bypassed, is this a common issue? I bought the car used and did not build it. Thanks, Brian Ward. 

[Ron Alan]

Had the same issue with 2 different cars. On the 1.6 it was in the harness right around the steering column...loosing fuel pump power. 

 

In the 99 it was the fuel pump UNIT...would start with a small miss/stumble around 1/2 a tank in a long/sustained left hand high g corner...would get worse as the fuel load got closer to empty. Changed the whole assembly...been gone ever since!

[shedguy]

Hey Brian I had the same problem in my 96. Changed the fuel pump and screen and the problem went away. Car would run fine with a full tank and start cutting out below a 1/2. Hope that's your problem its an easy fix.

[Danica Davison]

When the car shuts off, does your tach go to zero? Or does it just gradually fall like it would if you are off the throttle? 

 

Someone needs to confirm with this to make sure I have it correctly, but it is to my understanding that if the tach shuts off and goes to zero .. it is most likely an electrical issue.  And if it gradually falls like it would if you were coasting, it is most likely a fuel pump issue.

[Ron Alan]

^^^The reality is many things could cause the OP symptoms. In my 1.6 issue...the AFR jumped up to 22+ indicating loss of fuel...but it was an electrical issue in the FP B+ wire! So an electrical issue...but wasn't a whole car issue so no loss of tach or anything else.

 

IN another car of mine...was having a stumble between 6-7000rpm that was very intermittent(from nothing in the morning sessions to 2 small pops in a session to full missing a whole session)and shot gunning parts wasn't working! Finally installed an AFR hoping this would give me some insight! Sure enough...when the car would miss the AFR dropped indicating a fat mixture so was losing spark not fuel. Finally cut off and replaced the cam sensor plug(95 car)and it would seem so far this has solve the issue!

 

The theory in my 99 low fuel left hand turn stumble was a cracked pipe on the FP assemble that would suck air...I never confirmed this but had someone else tell me that is what they found on theirs with the same symptoms. All I know is replacing the whole FP assembly solved the problem!

[super B]

My tack stays up and running approx 5500 rpm as I can recall... it for sure does not drop to zero. Only sweeping left high g turns. IE. the carousel turn at Sebring. it does not stumble or give any sign its going to quit. just 2 or so seconds into the turn, its like you lifted off the gas.. For sure I am going to change the fuel pump .Thanks Brian

[Steve Scheifler]

Same symptoms on a 1.6 awhile back, happening From 1/2 tank and below. Fuel pump did not seem to make sense but a couple people told me to forget logic and just replace it. It worked.

[Danica Davison]

My tack stays up and running approx 5500 rpm as I can recall... it for sure does not drop to zero. Only sweeping left high g turns. IE. the carousel turn at Sebring. it does not stumble or give any sign its going to quit. just 2 or so seconds into the turn, its like you lifted off the gas.. For sure I am going to change the fuel pump .Thanks Brian

 

Yeah, I would replace the entire fuel pump and tree. I had the same issue with my old 1.6 once, it would cut out in the carousel at sebring and T6 at Daytona when it dropped below half a tank.  That worked for me

[Danny Steyn]

Do you have a fuel pressure gauge that is mapped to your data? If so you will immediately see the pressure drop if it is fuel related. If you do not map directly to a data system, can you see it in your video? Once again this will help you detect immediately if it is fuel related.

[MPR22]

Could be the dreaded broken baffle in the tank. 

 

Could be the ecu resetting.  I would think that would kill that tach though. 

[SaulSpeedwell]

Didn't read whole thread.  In-dash or data-logged fuel pressure gauge is the most underrated gauge of all time for SM and every other car, if you ask me, especially compared to the fancy but usually misleading on-board AFR gauge. 

 

For less than the cost of one wheel bearing, or one German Hoosier, or 0.002 the cost of your competitor's CoalMAX DuallyStroke Supreme Brougham Landau King Ranch Boss Hogg Harley Davidson Denali Edition tow vehicle, you would know for damn sure whether the miss/stumble was fuel pressure or something else.

[Steve Scheifler]

I'm guessing I can count on a single lap of my fingers the number of SMs with fuel pressure being logged, and not that many more with a gauge on the dash.  Which I suppose is to say that I agree with Saul, even though I have not installed either in our cars.  But if I could have only one or the other, it would be the "fancy but usually misleading on-board AFR gauge".

[Danny Steyn]

Didn't read whole thread.  In-dash or data-logged fuel pressure gauge is the most underrated gauge of all time for SM and every other car, if you ask me, especially compared to the fancy but usually misleading on-board AFR gauge. 

 

For less than the cost of one wheel bearing, or one German Hoosier, or 0.002 the cost of your competitor's CoalMAX DuallyStroke Supreme Brougham Landau King Ranch Boss Hogg Harley Davidson Denali Edition tow vehicle, you would know for damn sure whether the miss/stumble was fuel pressure or something else.

 

Could not agree with you more Saul!  At the recent Watkins Glen Hoosier Super Tour I actually did not feel or detect the fuel pressure stumble in the car. However in examining the data I was able to see it clearly, and brought it to Fowler's attention. We were fortunately able to change out the fuel pump before the main race and go on to stop the clock in Race 2.

 

Great believer in mapping the following to your in car data system (and always record the ambient conditions)

• Fuel Pressure
• AF Ratio
• Water Temp
• Throttle Position
• Brake Pressure 

[Marc Cefalo]

don't forget where the fuel pressure sensor is for your data systems......most 99-05 cars I've seen have it right at the regulator.....which is NOT where you want it......

[38bfast]

Danny from you plot I would not have replaced the pump. It looks like you were just running low on fuel. 

[SaulSpeedwell]

Danny from you plot I would not have replaced the pump. It looks like you were just running low on fuel. 

 

When the check valve went bad on my '99 fuel pump, it would do similarly "instantaneous" fuel pressure drops with anything less than ....say ... 3 gallons in the tank?  Only in sharp left turns, IIRC.   There may have been other pump problems beyond the check valve, but the line pressure would definitely drop to <15psi pretty much as soon as you keyed off.  And the engine wouldn't fire back up until 10+ crank revolutions and the fuel pressure got back to high 30s psi. 

 

I'd be curious what Danny's data said when the engine was keyed off. 

 

This is the #1 viewed video on my notoriously amateur and terrible YouTube channel ... a whopping 3,401 views!  LOL

 

[Steve Scheifler]

Speaking of pump failures, I don't suppose anyone but Mark has spent much time tearing them down? Are they typically just getting weak, or failing entirely? If the galling is typical even on low mileage failures, might the problem be that they briefly run dry each time we pump the tank empty? Also, I've always assumed that in normal operation the fuel running through them provides adequate cooling, but I had an experience on the dyno recently that lead me to believe the pump might be overheating. Adding a few gallons cleared it up. I guess that when driving with low fuel there would be plenty of splashing to keep it wet, but perhaps a long dyno session on low fuel is a bad idea. Anyone else see any indications of that?

[38bfast]

We have seen lots of pumps go weak. At idle they have good pressure but as you run up the RPM range to red line you will see the pressure drop. We have seen some drop as much as 15PSi through the range. You will see it as well on the AF gauge. Another good reason to log fuel pressure. We have had customers that aren't logging AF or FP cook a perfectly good motor down due to a bad pump. 

 

Looking at Dannys plot it appears that the fuel pressure spikes get worse lap after lap trending more towards a fuel starvation issue in the tank. Low fuel, broken off baffle, or return hose not pointed directly at the sock on the bottom of the fuel pump. 

[Bench Racer]

Don't disagree with logging fuel pressure.

Why do so few use a visible (outside the windshield)  fuel pressure gauge with snubber?

[Danny Steyn]

Danny from you plot I would not have replaced the pump. It looks like you were just running low on fuel. 

 

Ralph - no we were more than 50% at the time. We have had this occur twice now and replacing fuel pump cured it each time. Normally when a fule pump starts going bad, I feel the gas starvation, a hesitation, sluggish response, most often after a long loaded left hand turn  But as you can see from the data, the dip in fuel pressure did NOT coincide with any dip in engine performance.

 

The reason I showed the data trace is to demonstrate how useful logging these parameters are to help catching a situation early before it becomes a real issue.