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Hesitating While Driving - Fuel Pump?


bigcoconut
10-22-2008, 10:47 PM
99 van with 120,000 miles on it. Just got back from a trip to Kansas City, I live in Houston. Last summer I gave it a tune-up, plugs & wires and filters. Just changed the fuel filter before the trip. On the way up, no problems, smooth as glass. However, on the way home it started hesitating/bucking at highway speeds. Made it to Oklahoma City and stopped at a chevy dealer. The tech drove it and it was hesitating, he had his computer hooked up and it was showing to be running lean, why we don't know. Got back to the shop and hooked a fuel pressure gage and drove it around again, but it stopped hesitating, the pressure was right on the money the whole time. He checked the fuel for water or other contaminants and it was clean.

He said his best guess was the fuel pump, but he said it was a "$600 guess". It was running lean but no codes were recorded by the computer. It started running fine so I took a chance and we filled up and drove the rest of the way with no issues at all, smooth as glass all the way home.

That was a couple of weeks ago, no problems until now, it is hesitating again, just like before. Driving along nothing unusual, and it just starts bucking and then it goes away. I just filled the tank again, but this time it is still hesitating. No "Check Engine" light.

cjstew4
10-23-2008, 02:55 PM
99 van with 120,000 miles on it. Just got back from a trip to Kansas City, I live in Houston. Last summer I gave it a tune-up, plugs & wires and filters. Just changed the fuel filter before the trip. On the way up, no problems, smooth as glass. However, on the way home it started hesitating/bucking at highway speeds. Made it to Oklahoma City and stopped at a chevy dealer. The tech drove it and it was hesitating, he had his computer hooked up and it was showing to be running lean, why we don't know. Got back to the shop and hooked a fuel pressure gage and drove it around again, but it stopped hesitating, the pressure was right on the money the whole time. He checked the fuel for water or other contaminants and it was clean.

He said his best guess was the fuel pump, but he said it was a "$600 guess". It was running lean but no codes were recorded by the computer. It started running fine so I took a chance and we filled up and drove the rest of the way with no issues at all, smooth as glass all the way home.

That was a couple of weeks ago, no problems until now, it is hesitating again, just like before. Driving along nothing unusual, and it just starts bucking and then it goes away. I just filled the tank again, but this time it is still hesitating. No "Check Engine" light.

If the codes don't point to anything, I would run some gas treatment /injector cleaner through it before looking to the fuel pump.

rockwood84
10-24-2008, 10:52 AM
when it hesitated was it smooth highway or bumpy? because your problem could be in the pass-thru connector in the floorboard behind the drivers seat. it the bigger of the two connectors. it has the fuelpump wires, fuel gauge wires going thru it. this connector gets wet from a bad designed seal,the seal is supposed to keep the moisture out but does not.if the connector is green inside and the road is bumpy you could be loosing connection at the pins in the connector.sometimes the fuel gauge will go nuts as it hesitates.i have seen some that you could clean with electrical cleaner then gobb the connector full of diealectric cream. i can't remember how many pins in the coonector seems like it was six or eight . do not scrape on the pins much or they will break off.

bigcoconut
10-27-2008, 12:08 PM
It is still having problems, however, now sometime when it hesitiates it will stall. It restarts immendiately, like nothing is wrong.

No bumps or other sudden outside forces acting on the car, just smooth roads and all of the sudden it starts hesitating, the car slows down almost like an engine brake, and then it goes away and I can accelerate back to speed until next time.

I did run some injector cleaner in this last tank but haven't run through it yet, so I don't know if it worked.

Again, no codes are getting stored in the computer, the computer thinks everything is OK as far as what it monitors. The only thing it tells me is that the engine is running lean when it is hesitating, but why is it running lean I don't know.

bigcoconut
10-27-2008, 12:14 PM
Would the O2 sensor play a role in this? I figure if the O2 sensor is telling the computer that there is too much fuel in the exhaust then the computer would lean the mixture to compensate, when in reality that just thins the fuel already too much. Should the computer pick this up as a bad O2 sensor or could it be just enough of a voltage fluctuation to fool the computer for a second or two? Again, I'm getting no codes in the computer.

rockwood84
10-27-2008, 01:25 PM
Would the O2 sensor play a role in this? I figure if the O2 sensor is telling the computer that there is too much fuel in the exhaust then the computer would lean the mixture to compensate, when in reality that just thins the fuel already too much. Should the computer pick this up as a bad O2 sensor or could it be just enough of a voltage fluctuation to fool the computer for a second or two? Again, I'm getting no codes in the computer. i'm still thinking that the fuelpump is back pressuring. running but not pumping close to 50 pounds pressure. the pressure is probably down to 20-30 pounds and this is not enough to keep the motor running at highway speed,so it slows down .these fuelpumps are bad about this.to find this you have to put a fuel gauge on the fuel line.i put mine on the fueline where the fuel filter goes.and just leave the key on and watch the pressure or you can rig one to fit in like the fuelfilter and put a long hose on it and put the pressure gauge on the dash where you can see it when it acts up.this takes a little more rigging but you can drive it and then see whats going on with the fuel pressure when it acts up. you just have to make a fitting and tubing to fit where the fuelfilter goes and not leak. did you check the pass-thru connector? could be the connector on top of the fuel pump as these will go bad .g.m. used too small gauge of wire when they made them and they get hot and go bad.mine would like yours then it got to bucking and backfiring. but five minutes later it would run 100 mph for as long as you wanted to hold it there. then 3 hours later same bucking. finally rigged up the drivo-gauge and when it would start bucking and backfiring it had a fuel pressure of 20 pounds then go down to 10 pounds back up to 20 pounds.put a new $320.00 fuelpump in and cured it.i used the nipples off of an old fuel filter and put a "t" between them and got 4 foot of hose to put through the window to put the fuelgauge on the end of it.one hint that the connector on top of fuelpump or the passthru connector will give is that the fuel gauge on the dash will act up. if its just a worn out fuelpump the fuel gauge won't act up[go to empty or any other mark ,other than whats actually in the tank]. the reason your getting a lean burn is low fuel pressure.if you get a code to pop it will be for a lean burn and it could be anything associated with a lean burn,tps code. if it backfires or bucks it will pop a code for camsensor ,crankshaft sensor, and tps sensor.but i'm betting on the fuelpump doing the backpressure thing. good luck :banghead:

bigcoconut
10-27-2008, 01:35 PM
Fuel gauge is working just fine, no issues there. The dealer did run a fuel pressure gage taped to the window when we were in OKC, but it never acted up, the pressure was good (per the tech, I couldn't read it from where I was sitting) the whole time.

I'll try to rig a pressure gauge this week and drive it around, I'll let yo know what I find...

Schrade
10-28-2008, 10:53 AM
I'll try to rig a pressure gauge this week and drive it around, I'll let yo know what I find...

EXCELLENT!!! Diagnostics!!! GOOD WORK!




He said his best guess was the fuel pump, but he said it was a "$600 guess".
This was not a mechanic that said this right? This was a friend who knows little about cars? Because if it was a mechanic, I would say, "I guess I WON'T pay you if it doesn't fix the problem.", and then I'd say, "Never mind, that's not a guess, it's a definite - I WON'T pay."

Do an ohm test of the injectors. Hot, and cold.

Post results.

pastaben
10-31-2008, 11:16 PM
sounds like a problem I had on a couple of occasions:
1. kinked throttle cable under hood. some mechanic pushed it out of the way to get at something and left it there, but had to replace it because it was kinked.

2. about 30K miles later, similar symptoms, and replacing the ignition coils did the trick.

bigcoconut
11-03-2008, 08:36 AM
OK, I didn't run a pressure gauge on the fuel system like I said. I did a knee jerk reaction, the mechanic in OKC said "maybe" Fuel Pump so that's what I did this weekend along with the fuel filter and guess what, no change )$%&*@#*%^@*(:mad: .

So here I am, new fuel pump assy (the whole "kit"). Just dropped the tank, unscrewed the big a$$ black ring, pulled old fuel pump assy out and put the new one in and reverse order everything back together. Pretty easy stuff, the hardest part was making sure I didn't blow myself up with the fumes, thank goodness it was a clear weekend. There was one catch, it came with a new electrical pigtail because the connection at the top of the pump was different. It also had me install a 20A fuse in place of the original 15A at the fuse block (#32 for the fuel pump).

OK, so I'm at square one again, the engine hesitates/slows down (it isn't stalling) at all speeds, just taking off and cruising along, the van slows down, jerks around a bit, and then it comes back and I can accelerate again. BTW all this bagan after my 100,000 mile tune-up, new plugs (Bosch), new wires (AC/Delco), filters (air and oil), PCV, fluids check, and new fuel pump assy, etc...

My assumption now is the fuel delivery system is OK up to the injectors, there is something telling the computer to lean the fuel mixture or something is leaning the fuel mixture on its own, and the computer isn't catching it because there are still NO CODES. BTW, ran a tank of "injector cleaner" with no change, just filled up second tank with "injector cleaner" for a second dose.

rockwood84
11-03-2008, 11:55 AM
at 120,000 miles the fuelpump was about to the end of its life anyway .some of these mexican made fuelpumps [thanks to nafta] don't make it past 90,000 miles.did you check the connector in the floor board? one other thing ohm the tps [ the numbers should change as you move the notch back and forth.and see if it is in the notch on the throttle body should be centered with notch in the groove on the tps.if its not centered it will throw off the computer.or the tps could be cracked does it act like a miss or series of misses? did you get the map sensor hoses and wires back on? since it started after the 100,000 mile tune -up check that all the connectors are on and every hose is hooked up. its easy to knock one loose or an old hose to break.pull the vacumn line off the fuel regulator and see if gas comes out.

bigcoconut
11-03-2008, 12:49 PM
All underbody connections are good, checked them and used dielectric grease on all.

It feels like a series of misses, not just one but multiple cyclinders.

Triple checked the MAP sensor hoses, had them reversed after tune-up, ran like crud for awhile and through a code (don't remember what but it pointed me right to the MAP sensor). All's good now, as far as that is concerned.

I can check the TPS (throttle position sensor) tonight, thats relatively simple to do I think, I'll post results. While there I'll triple check all my connections again.

bigcoconut
11-03-2008, 12:54 PM
Give me a hint as to where the fuel regulator is, I've got a GM maintenance manual on this thing, reads like stereo intructions (need a class on those things), but it's good at procedures once I nail a part down.

merc81
11-03-2008, 02:02 PM
Here is a photo of the fuel regulator with the vacuum line removed.
John

http://cemrweb.cemr.wvu.edu/~mathews/venture/fuel-reg.jpg

rockwood84
11-03-2008, 05:46 PM
could be a coil getting hot but it would keep missing until you shut the motor off then it would run fine until it got hot again.in other words it wouldn't run fine then miss then run fine.and the 7x cranksensor on the backside of the motor could make it miss but should pop a code .as any miss fire should have popped a code.if the 24x cranksensor behind the harmonic balancer was acting up the tach would get screwy then eventually it wouldn't even crank up.

bigcoconut
11-03-2008, 10:48 PM
Fuel Regulator - poped the hose off, no fuel present, hose is dry, no gas smell.

TPS - looks OK, no cracking visible, Couldn't get to it tonight, have to pull it tomorrow to inspect.

FYI - Driving around this evening I noticed that when it starts hesitating I have to let off the gas to get it to calm down. If I keep my foot in the gas or try to accelerate, it will continue hesitating unitl I take my foot off the gas. I don't know what that means exactly, just another clue. It happens hot or cold. It seems to act up only during heavy load. If I accelerate real gradual/slow (old ladies passing me slow) it seems to be OK, only during load will it act up.

What about the EGR valve? If it were plugged would it act this way.

I found a new friend Sunday, one of the other dads on my sons baseball team is a tranny mechanic at a local Pontiac/GMC dealer. He told me to give him call and he can bring one of their diagnostic computers home and he'll hook it up and see what it says as we drive. I'm going to give him a call tomorrow and try to get together tomorrow evening.

cjstew4
11-04-2008, 03:59 PM
(http://fixitnow.com/samurai-certification-for-electronic-circuit-board-analysis-examination/)
Maybe one of those leaves got somewhere it should not have and is plugging it up. Get those out of there.
Head gaskets leaks will impede performance as well. No overheating??? Right.
Are you sure you don't also hear a knocking somewhere. My 97 had a stuck lifter in the front 3 and caused some god-awful performance until I changed the oil 3 times with different oil treatment brands until the last one with Risoline proved to work. Saved many hundred $ on this technique that my mechanic recommended. He also said to run a qt of Risoline thru at every other oil change. Have since and no stuck lifters now going on 176k miles. !!!!!!!!!!
http://cemrweb.cemr.wvu.edu/~mathews/venture/fuel-reg.jpg[/quote]

Schrade
11-04-2008, 11:46 PM
OK, I didn't run a pressure gauge on the fuel system like I said. I did a knee jerk reaction, the mechanic in OKC said "maybe" Fuel Pump so that's what I did this weekend along with the fuel filter and guess what, no change )$%&*@#*%^@*(:mad: .

So here I am, new fuel pump assy (the whole "kit"). Just dropped the tank, unscrewed the big a$$ black ring, pulled old fuel pump assy out and put the new one in and reverse order everything back together. Pretty easy stuff, the hardest part was making sure I didn't blow myself up with the fumes, thank goodness it was a clear weekend. There was one catch, it came with a new electrical pigtail because the connection at the top of the pump was different. It also had me install a 20A fuse in place of the original 15A at the fuse block (#32 for the fuel pump).

OK, so I'm at square one again, the engine hesitates/slows down (it isn't stalling) at all speeds, just taking off and cruising along, the van slows down, jerks around a bit, and then it comes back and I can accelerate again. BTW all this bagan after my 100,000 mile tune-up, new plugs (Bosch), new wires (AC/Delco), filters (air and oil), PCV, fluids check, and new fuel pump assy, etc...

My assumption now is the fuel delivery system is OK up to the injectors, there is something telling the computer to lean the fuel mixture or something is leaning the fuel mixture on its own, and the computer isn't catching it because there are still NO CODES. BTW, ran a tank of "injector cleaner" with no change, just filled up second tank with "injector cleaner" for a second dose.

No you didn't... You did not replace the fuel pump without checkin' pressure did you? You rich? Can I have some money?

the mechanic in OKC said "maybe" Fuel Pump
Maybe the air freshener too.

120,000 miles the fuelpump was about to the end of its life anyway Only the psychic hotline knows when the fuel pump is about to the end of its life anyway.

Me: Do an ohm test of the injectors. Hot, and cold. Yup. Test fuel pressure too.

He told me to give him call and he can bring one of their diagnostic computers home and he'll hook it up and see what it says as we drive. I'm going to give him a call tomorrow and try to get together tomorrow evening.
What did this scan show?

bigcoconut
11-05-2008, 08:40 AM
OK, here goes, apparently the van has a little stage fright, she won't perform when being watched. She hesitated a little just out of the neighborhood on my way to my buddies house, but for the next 17 miles, no problems.

When I got there he hooked up the Tech II while it was idling and of course everything is showing just OkeeDokee - no codes, fuel pressure good, HO2S1 & 2 good, voltage good, and the host of other variables we looked at were all normal. He got in and we drove for about another 20 miles and no performance, the gremlin never came out of the side curtains to do his little dance.

OK, so we shut the van down for a little world problem solving, no beer, and let the cool evening air cool down the motor.

After letting it cool down, we hooked up the Tech II again and we started up the van. At idle no issues, revved the engine a little, again no issues. Put her in drive and stepped on the gas, and horse came out of the shoot. So he's trying to drive, hangin on to the steering wheel and looking at the Tech II, I'm a little nervous in the passenger seat, but he's done this before. The van is hesitating - if you keep your foot in the gas it will stay bucking for awhile, you have to take your foot off the gas to get her settle down. Again, in a nutshell, with the van hesitating and coughing, the Tech II is showing everything is Freak'n OkeeDokee???

Fuel pressure - good
HO2S1 & 2 - good
Voltage - good
Misfires - none
MAF - good

I can't remember all of the stuff he showed me that we looked at, man that Tech II reads a whole bunch of stuff from the computer/sensors. One thing he did mention was weird was that when the van started hesitating the system (I'm guessing coolant) went into closed mode. He told me it stays in the open mode until the engine warms up to about 160F and then goes into closed mode. With the engine cold it went into closed mode during the hesitating.:confused:

So, in the mist of all of this he notices the battery light flashed during one of its hesitating episodes, but again the system voltage never fluctuated.:confused:

After the van warmed up the gremlin went back to his dressing room and didn't come back out on stage:banghead: . He told he would talk to one of his buddies at the shop about this gremlin and let me know some more this afternoon. He says its the ignition system, something is killing the power to the ignition system intermittently, not enough to stall/kill the motor but enough to slow it down, thats why the battery light flashed but the voltage never dropped.

Thats all I got so far, had to get home and diagnose the clothes washer, the wife called me and says something came apart in the tub and their are rusty pieces all over the place.:shakehead

Schrade
11-05-2008, 11:01 AM
Get the ignition module tested at Advance / Zone. Free test, get it done HOT. It will unscrew with 2 small screws.


One thing he did mention was weird was that when the van started hesitating the system (I'm guessing coolant) went into closed mode. He told me it stays in the open mode until the engine warms up to about 160F and then goes into closed mode. With the engine cold it went into closed mode during the hesitating.
Are you sure it was cold when it went to closed loop? 'Cause it warms back up very quickly, even tho' you say it cooled in the evenin' air. ??? I think it had probably reached the closed mode temp, which is normal.

I think you have one of 2 things:
1) If poor performance started AT THE MOMENT OF CLOSED LOOP, the problem is fuel, because that's when the fuel goes from max fuel, to minimum fuel. That's a fuel problem of insufficient pressure for vaporization, or bad injectors (did you ever do the ohm test?).

2) I don't believe it went closed loop while it was still cold. It had probably reached the critical temp. BUT, if it did go closed loop while cold, either the signal from the O2 was erroneous, or the engine temp sensor is sendin' a bad signal. Exhaust temp is the first determinant, coolant temp is second (I think).

The battery light I think is only because the motor was cuttin' out, not the other way around.

bigcoconut
11-05-2008, 12:16 PM
Have not done the Ohms test on injectors yet. I'll look in the service manual tonight to find out how to do this.

When you say "ignition module" do you mean the control module (pic below, item #3, the service manual calls it a "control" module) the plate that the coil paks mount to, or is their something else I'm looking for? BTW looking at this image, I have no "seals" (item #2) between the coil paks and the ignition module, should there be??? ((forget this, there are 'seals' at the base of the pins)) When I put everything back together after the tune-up I put dielectric grease on the control module pins that the coil paks stab onto, I'm thinking that is not a problem???

http://i28.photobucket.com/albums/c242/xeroinfinity/fisslesticks/V6ignitionsystem.jpg

scottnhalifax
11-05-2008, 03:17 PM
not sure if this will help, my pop lesabre 3.8 seems like it has the same issuses, what we found the problem to be was a faulty oil sender low oil pressure shuts down a relay and cut power off to the fuel injectors. seems like it starts to chug, doesnt throw any codes, just acts like sh1t. new oil sender and no problem now
just my 2 cents
scott

cjstew4
11-05-2008, 07:06 PM
OK, here goes, apparently the van has a little stage fright, she won't perform when being watched. She hesitated a little just out of the neighborhood on my way to my buddies house, but for the next 17 miles, no problems.

When I got there he hooked up the Tech II while it was idling and of course everything is showing just OkeeDokee - no codes, fuel pressure good, HO2S1 & 2 good, voltage good, and the host of other variables we looked at were all normal. He got in and we drove for about another 20 miles and no performance, the gremlin never came out of the side curtains to do his little dance.

OK, so we shut the van down for a little world problem solving, no beer, and let the cool evening air cool down the motor.

After letting it cool down, we hooked up the Tech II again and we started up the van. At idle no issues, revved the engine a little, again no issues. Put her in drive and stepped on the gas, and horse came out of the shoot. So he's trying to drive, hangin on to the steering wheel and looking at the Tech II, I'm a little nervous in the passenger seat, but he's done this before. The van is hesitating - if you keep your foot in the gas it will stay bucking for awhile, you have to take your foot off the gas to get her settle down. Again, in a nutshell, with the van hesitating and coughing, the Tech II is showing everything is Freak'n OkeeDokee???

Fuel pressure - good
HO2S1 & 2 - good
Voltage - good
Misfires - none
MAF - good

I can't remember all of the stuff he showed me that we looked at, man that Tech II reads a whole bunch of stuff from the computer/sensors. One thing he did mention was weird was that when the van started hesitating the system (I'm guessing coolant) went into closed mode. He told me it stays in the open mode until the engine warms up to about 160F and then goes into closed mode. With the engine cold it went into closed mode during the hesitating.:confused:

So, in the mist of all of this he notices the battery light flashed during one of its hesitating episodes, but again the system voltage never fluctuated.:confused:

After the van warmed up the gremlin went back to his dressing room and didn't come back out on stage:banghead: . He told he would talk to one of his buddies at the shop about this gremlin and let me know some more this afternoon. He says its the ignition system, something is killing the power to the ignition system intermittently, not enough to stall/kill the motor but enough to slow it down, thats why the battery light flashed but the voltage never dropped.

Thats all I got so far, had to get home and diagnose the clothes washer, the wife called me and says something came apart in the tub and their are rusty pieces all over the place.:shakehead

Can only help you with the washer repair. Check out this site that offers free appliance repair help and returnable parts within 30days, even electrical ones. Used it many times. Great resource. http://fixitnow.com/.

bigcoconut
11-10-2008, 09:50 AM
Cracked ignition control module (the black plastic plate the coils mount to)!

This weekend I spent Saturday taking everything electronic off of the top of the motor and inspecting it. Found both crank sensors (24X and 7X), a little greasy and road grime, otherwise seemed to be OK and wiring. Also found the cam sensor, PITA to get to under the power steering pump, but seemed to be OK. Pulled the coils (two were original and one was newer, about two years old). When I got the ignition control module off I pulled the rubber gaskets under where the coils mount and found cracks between the coil pins. My only guess is I tightened them to much when I last re-installed. Found the module at Advanced auto for 80 bucks and I went ahead and replaced the two older coils (40 bucks each).

Running and idling much better now. However, this problem has fooled me before, thinking it was gone. I'll have to drive it awhile to make sure.

Happy Trails...

xsonymanx
03-09-2010, 09:05 AM
Hi,
Is there solution for this. I have a 2001 Venture doin the same thing, first had no spark at all.... then took it to a repair place no codes etc etc... so he GUESSED the ignition Control Module ( * used one from a yard * ) and whallah ... it fires up....was fine for 2 days ( about 200 miles ) NOW at random times no matter what speed. it may go for 2 minutes or 40 minutes with no problems,,, Then it will just start jumpin , wont accelerate, when the pedal is pressed have to let off the pedal to calm it down etc etc. No codes to the "T" as this thread describes.
Only thing i can think of is A NEW Ignition Control Module, AND/OR Ignition Coils... Please if someone knows please reply: xsonymanx@yahoo.com Thanx in advance

xsonymanx
03-18-2010, 10:41 PM
FYI....
This turned out to be an Ignition Control Module In my case... same symptoms as stated above. i Purchase a new ICM from RockAuto ( dot) com for $ 57.00 shipped about 1/2 price of what would be paid for it in my local auto parts store. Local mechanic put it on for me for 40 bucks.
hope this helps.

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