Hesitating @ highway speeds - light load. Pump?

[swharris]

'97 Astro is now starting to miss/hesitate at freeway speeds @ light load (very noticable with cruise on).

Background:
280,000 miles
New fuel pump (4th in lifetime), spider,dist., cap, rotor, wires, plugs, timing chain, oil pump, coil, etc. done 10k miles ago.

Van had been running fantastic, but now hesitates at cruising speed at light throttle. Could this be once again ANOTHER fuel pump??? Once I get a chance I'll throw a pressure gauge on it and drive it around and try and replicate the problem to see if the pressure drops. Does anyone make a pressure gauge extension hose??

If this is the FP, it will be the van's 5th! I don't replace things lightly, and every pump was verified as a failure. Stupid van

[Spider'sSafari]

It may is a simple as water in fuel, thanks to Ethanol gas blends. I attached a great write up of Why it can be so bad, it's has alot of good info and can explain a lot of little runninng problems that are just fuel related.

The 10% that could be as it's posted on the pump is not regulated and the gas/ethonal blend is done by the guy who delivers the fuel to the station. So the supplier doesn't even store it and keeps the 2 seperate until they put it in the tank in the ground.. Problem = Smaller stations that don't move alot of product can develop alot of seperation it the ground tanks and when they do get low the customer gets more alcohol or water then regular gas and no real fix for them, they probably don't reallly even care or know what's happening.
So, it's best to buy gas at busy station with alot of turn over, but they also maybe mixing too much Alcohol to stretch the gas and make more $$$$. The 10% is not regulated by the Government and it's up to each provider to get it right.

Easy fix might be Drain tank, top off with higher Octane and run some Seafoam through it. Also Don't run the tanks below 1/4 level so you don't get a chance to suck up the junk that could be in the tank.

Please Read This::;; http://www.fuel-testers.com/ethanol_pro ... amage.html

[swharris]

Thanks for the suggestion. I put about 375-500 miles a week on this van, so I go through a bunch of gas from various stations. The issue has transcended multiple tanks, so I'd doubt it was moisture. I'm in dry So. CA too and moisture is usually not an issue. Still, I'll most likely drop the tank and see what's going on in there. The gas gauge is broken and I suspect it is the sender. I have a spare pump/sender so hopefully that will fix it. It's never a guarantee with this platform though It's a crime that these pumps continue to fail with such regularity. Chevrolet should have been made to fix this issue and file a formal recall. A car should not go through 5 pumps in it's lifetime IMO.

[Spider'sSafari]

The water comes from the Fuel not the environment your in. Flushing it out can'r hurt.
Have you thought about removing the pump from the tank and just use an external electric aftermarket?

[Ragenme]

Spider'sSafari is right. That would be the way I'd go. I would also look in the tank while its down. If you have some trash in the tank it could cause a blockage. How long has this pump been in service. Also how often do you run it low? As you know that could be adding extra stress to the pump.

[swharris]

Spider'sSafari is right. That would be the way I'd go. I would also look in the tank while its down. If you have some trash in the tank it could cause a blockage. How long has this pump been in service. Also how often do you run it low? As you know that could be adding extra stress to the pump.

The last pump I put in about 2 years ago. I did significant service to the motor(see above) at the time and the van has run brilliantly since then. When the last pump went in, the tank was spotless. I also upgraded the connector at the pump with the factory suggested (TSB recommended) harness.

I try not to run the tank too low. Since the gauge quit, I've been running about 300 miles and then filling. I get about 20 mpg. The tank is 20gal.??

I'm going to get an extension for my FP gauge and drive it and see if pressure fluxuateswhen the hesitation happens. If not I guess the issue is electrical, and I can start looking at cap/rotor/wires/plugs. All that was new at the 1.5 year interval too. New distributor went in then too(car had 230k at that point).

I

[chevymaher]

Another thing to check is the EGR valve. If it is sticking or staying open to much it will do that.

[swharris]

Spider'sSafari is right. That would be the way I'd go. I would also look in the tank while its down. If you have some trash in the tank it could cause a blockage. How long has this pump been in service. Also how often do you run it low? As you know that could be adding extra stress to the pump.

The last pump I put in about 2 years ago. I did significant service to the motor(see above) at the time and the van has run brilliantly since then. When the last pump went in, the tank was spotless. I also upgraded the connector at the pump with the factory suggested (TSB recommended) harness.

I try not to run the tank too low. Since the gauge quit, I've been running about 300 miles and then filling. I get about 20 mpg. The tank is 20gal.??

I'm going to get an extension for my FP gauge so I can see it in the cabin, and drive it and see if pressure fluxuates when the hesitation happens. If not I guess the issue is electrical, and I can start looking at cap/rotor/wires/plugs. All that was new at the 1.5 year interval too. New distributor went in then too(car had 230k at that point).

[adam728]

For a miss at idle I'd start with electrical. If it were low on fuel pressure it would only get worse as load and flow rate increases.

Best bet would be to take it to someone that can hook up a scanner. Even if it's not throwing codes for the miss they can often tell a lot by the live data.

[MuRKRoW]

Check the EGR valve like chevymaher said. I had that problem and my van would stall while I was driving. I also didn't hear you talk about replacing the fuel filter. Maybe there's a blockage in it? Who knows. You'll need to pressure check it. You don't need to be driving to check the fuel pressure...

4 fuel pumps is way too many already. I haven't had to change mine even once. I'm at 127K miles too. Are you buying off-brand pumps? Buy AC Delco parts whenever possible for now on. http://www.autopartswarehouse.com/detai ... EP381.html

If you can't find pressure problems in the fuel system, then the ignition system is the next place to start!

[swharris]

Check the EGR valve like chevymaher said. I had that problem and my van would stall while I was driving. I also didn't hear you talk about replacing the fuel filter. Maybe there's a blockage in it? Who knows. You'll need to pressure check it. You don't need to be driving to check the fuel pressure...

4 fuel pumps is way too many already. I haven't had to change mine even once. I'm at 127K miles too. Are you buying off-brand pumps? Buy AC Delco parts whenever possible for now on. http://www.autopartswarehouse.com/detai ... EP381.html

If you can't find pressure problems in the fuel system, then the ignition system is the next place to start!

It is 4 pumps if you count the original pump. 1st replacement was done by a dealer(on vacation and in a lurch with out any of my tools) so I assume it was a Delco(it ought to be for the $600 I paid those thiefs), second one was an off brand, but the third replacement was Delco. New fuel filter at each replacement, so I doubt that is the issue.

I beg to differ for the need to test while driving. The last pump that failed worked perfectly and put out spec. psi @ idle and while key on. It even put out perfect pressure @ around town driving. BUT, once the ambient temp went 90+ and at highway speeds the pressure dropped to 20psi and would not return until things cooled off. This took me months to figure out. I now test while doing ACTUAL real world driving conditions and temperature.

Thanks for the tips.

S.

[swharris]

Check the EGR valve like chevymaher said. I had that problem and my van would stall while I was driving. I also didn't hear you talk about replacing the fuel filter. Maybe there's a blockage in it? Who knows. You'll need to pressure check it. You don't need to be driving to check the fuel pressure...

4 fuel pumps is way too many already. I haven't had to change mine even once. I'm at 127K miles too. Are you buying off-brand pumps? Buy AC Delco parts whenever possible for now on. http://www.autopartswarehouse.com/detai ... EP381.html

If you can't find pressure problems in the fuel system, then the ignition system is the next place to start!

Pre 96 van? If so, the pumps are apples and oranges. The failure rate for the earlier pumps are a fraction of the later ('96-later). Post '96 pumps are 3 times the price too. So, comparing a pre facelift van pump to the later ones is not a fair comparison.
http://www.autopartswarehouse.com/sku/GMC/Safari/AC_Delco/Fuel_Pump/1997/SLE/6_Cyl_4-dot-3L/ACMU1782.htmll

[JuneauCabbie]

If this is the FP, it will be the van's 5th! I don't replace things lightly, and every pump was verified as a failure. Stupid van

Are you letting the gas level get low before refueling? These pumps use the fuel as a coolant, so you should never let the fuel level in the tank get below 25% full. Capacity for my '03 tank is 23 gallons (20 + 3 "emergency"), so I never let it get below about 6 gallons.

If you've had that many pump failures, overheating because of low fuel levels could be the cause.

[adam728]

If this is the FP, it will be the van's 5th! I don't replace things lightly, and every pump was verified as a failure. Stupid van

Are you letting the gas level get low before refueling? These pumps use the fuel as a coolant, so you should never let the fuel level in the tank get below 25% full. Capacity for my '03 tank is 23 gallons (20 + 3 "emergency"), so I never let it get below about 6 gallons.

If you've had that many pump failures, overheating because of low fuel levels could be the cause.

Very common myth.

Fuel does cool the pump, but it's the fuel that runs THROUGH it, not the fuel around the outside of it. Running low won't hurt, unless you are in the habit of running it till the pump is sucking air.

[swharris]

If this is the FP, it will be the van's 5th! I don't replace things lightly, and every pump was verified as a failure. Stupid van

Are you letting the gas level get low before refueling? These pumps use the fuel as a coolant, so you should never let the fuel level in the tank get below 25% full. Capacity for my '03 tank is 23 gallons (20 + 3 "emergency"), so I never let it get below about 6 gallons.

If you've had that many pump failures, overheating because of low fuel levels could be the cause.

No. I refill at about 1/4 left in the tank.

**UPDATE** PROBLEM SOLVED!

Well, I pulled the dog house off to put a FP gauge on the test port. Pump is putting out 60psi at key on and then settles to around 55-57 running/driving as it should.

In addition to the hesitating issue I had also been neglecting a vent vacuum issue. The vents were not changing with the selector knob. This is usually a broken vacuum line coming from the intake manifold. So, while investigating the line I found that it was slightly cracked in multiple places. The last time I replaced it I used the factory hard line with the molded in end. Once I pulled the line and thought about it, it dawned on me that the hesitation I'd been experiencing could be from a momentary lean condition when the line would allow un-metered air in to the intake system. This would explain why the hesitation only occurred during times of high vacuum conditions(light throttle).

I replace the line and went for a drive on the fwy. Voila! No more hesitation!! For once a simple fix. I'm sure it'll be 10 years before I get another one

Anyway...check that stupid vacuum line first!! I will from now on. Oh and DON'T USE THE FACTORY HARD LINE...it will fail!

Thanks for all the comments guys )

[xit]

Glad you found your problem, it may help someone down the line