Hesitating/Surging and Popping under Load

Lunch Box · Apr 12, 2008

i have a 1988 LX 5.0 SD

Mods:

A/C Smog Delete
timing 13*
Mac LTs
Mac o.r Prochamber
Flowmaster
3.73s

okay under load and this is about 90% of hte time the car surges and or hesitates, like fuel is being completely cut off to the engine and it starts to make a popping noise

it is intermittent, for example leaving work today it ran like a gem while ****ing aorund with my buddies vette, but i got home parked it couple hours later took it back out and it ran like crap about, surging and popping noises and what ever else... its under and kind of load it happens but under WOT it will not happen as long but under partial load somtimes it just keeps going so i have to let off and push the clutch in....

say im rolling in first gear... at 2500 rpms the car will start bucking like fuel is just being cut off

the Pump is new
the Cap Rotor Plugs are new

this started happening shortly after my Exhuast was put in. i did run the car for a week with out O2s just had hte holes plugged because i was waiting for the extensions in the mail... and it just got worse and worse till where it is now that i just know when i hit the throttle and let the clutch out the car is just gonna pull the same old BS.

BlownFiveLiter · Apr 12, 2008

Check out the Surging Idle Checklist that's found in the Useful Technical Thread Index that's stickied at the top of this forum.

Lunch Box · Apr 12, 2008

its almost always under load

a couple times while idleing ill catch the rpms dipping pretty low but its 90% of the time while under load

mustangfan1990 · Apr 12, 2008

this might sound crazy but I went 2 years trying to find out what was wrong with mine when it did that and I had an optima battery and it was bad

Lunch Box · Apr 12, 2008

mustangfan1990 said:
this might sound crazy but I went 2 years trying to find out what was wrong with mine when it did that and I had an optima battery and it was bad

nah this is clearly (in my eyes) a fuel delivery issue but on the off chance its a ignition please chime in

Ddaniels750 · Apr 13, 2008

I also had a similar problem under part throttle and it turned out to be the HEGO ground. It's an orange wire that extends from the engine harness to the back of the engine. Somehow it had broken and caused all kinds of grief.

mustangfan1990 · Apr 13, 2008

Lunch Box said:
nah this is clearly (in my eyes) a fuel delivery issue but on the off chance its a ignition please chime in

I thought the same too. It sounded like a fuel delivery problem. When I posted problems about it on here that was what everyone was telling me.

Here is mine http://forums.stangnet.com/showthread.php?t=727800

vikingpower · Apr 13, 2008

TPS sensor may be broken, so the ECU is not reading open throttle. All you need is a voltmeter to check it.

blueblazes · Apr 13, 2008

this is a problem with the way the ecm gets data to decide how much fuel the car needs. Reason I say this is because you say its fine when its at wot, which means the computer is going off of known good values rather than trying to calculate from sensors and what not.

I would check the following:
1. Maf - get some electronics safe carb cleaner
2. tps
3. iac
4. as always check all your grounds

are you throwing a check engine light? If so you can check the code with the self test plug under the hood and count the times the cel blinks.

Lunch Box · Apr 14, 2008

from time to to at idle it dips down low and stuff but not very often, and even at WOT somtimes it will still not be 100%

svtpower · Apr 14, 2008

similar

My 87 SD does a similar thing. I am dumping a truckload of parts into it currently so I'm hoping to have the issue solved, but I won't know for a few weeks and it's back together.

Mine would only happen at WOT under load. It would pop through the intake and fall on it's face and hesitate. Happened more when it was cold, after it was warmed up it rarely happened.

I replaced a cracked vacuum hose and it got better but still did it. The car always smelled like it was running rich and the EGR and air intake passages were absolutely caked with carbon as was the old exhaust I took off when I got it to put on my Magnaflow stuff.

I have (8) 19lb injectors that have been sonically cleaned with flows sheets. My guess is I had a leaky injector, but we will see. The originals were really grimey looking. The upper and lower intakes are now spotless and ported so that should help too. I have a new FMS 65mm TB and spacer and it has a new TPS on it so that could be a fix too.

I have a code reader with a digital readout and there are no codes.

Shutgun approach?

Lunch Box · Apr 14, 2008

hmmm the IAC how do i get that thing off... every time i trie i always end up stripping the screws

svtpower · Apr 14, 2008

IAC

Just make sure you pick a screwdriver with a head that matches the screw heads the closest. I used a large screwdriver with a shallow head and they came out pretty easy. You don't want any wiggle room between the screwdriver head and the slots on the screw heads.

Lunch Box · Apr 15, 2008

this is wierd... on my vert the IAC has held in with screws, on my hatch now its held in with bolts...

mustangfan1990 · Apr 15, 2008

Lunch Box said:
this is wierd... on my vert the IAC has held in with screws, on my hatch now its held in with bolts...

Someone prolly changed it because they stripped out the screws...it is common in 5.0s to do that I did.

Lunch Box · Apr 28, 2008

Okay im still having this problem haha

So far i've done

Cap
Rotor
Fuel Filter
Fuel Pump
ACT sensor
MAP sensor (not a typo the MAP or BAP I AM SPEED DENSITY!)
Timing down to 13*
Cleaned IAC
EGR Delete
New upper intake Gasket (somone said somthing like the intake gasket could be leaking and letting in air that hte computer is not seeing.)
Wires

Checked TPS .74v at idle couldn't get a reading under throttle cuz i did it solo and i had to hold the lead tips on the pins

Checked the HEGO ground to the back of the block

Waiting on Doing the Fuel Pressure Regulator, just need a guage to adjust it.
Gonna get a New ECT sensor also.

(and can any one tell me where the coolant temp sender is? my guage in my car does not work)

ls1beater4eva · Apr 28, 2008

coolent temp is on the front driver side of the lowerintake manifold, what kind of ignition is on the car is it msd ?

LtDavis · Apr 28, 2008

Lunch Box said:
Okay im still having this problem haha

So far i've done

Cap
Rotor
Fuel Filter
Fuel Pump
ACT sensor
MAP sensor (not a typo the MAP or BAP I AM SPEED DENSITY!)
Timing down to 13*
Cleaned IAC
EGR Delete
New upper intake Gasket (somone said somthing like the intake gasket could be leaking and letting in air that hte computer is not seeing.)
Wires

Checked TPS .74v at idle couldn't get a reading under throttle cuz i did it solo and i had to hold the lead tips on the pins

Checked the HEGO ground to the back of the block

Waiting on Doing the Fuel Pressure Regulator, just need a guage to adjust it.
Gonna get a New ECT sensor also.

(and can any one tell me where the coolant temp sender is? my guage in my car does not work)

What about the oxygen sensors? My car was acting the same way when I realized the wiring was fraying and coming loose out of the actual sensor part. I'm sure they were old and needed replaced anyway but two new o2s fixed the problem.

ls1beater4eva · Apr 28, 2008

thats a really good point too bc it would make sense on why it only does it occasionaly, pull the codes

Lunch Box · Apr 29, 2008

02s are only a couple months old... and i ran the car for about a week and a half before this problem started with out 02s and once i put the 02s in the car it did not fix it.

Hesitating/Surging and Popping under Load

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