86 not running right

tehcarguy

Member
The problems started when my dad ran the car out of gas. This ruined the fuel pump, but I didn't know it at the time. I tried to start the car by spraying some starting fluid in the TB, and I think that may have hurt some of the sensors on it. If it did, wouldn't it be giving me a code? The problem is, when I drive the car for less than a mile, the engine starts surging and the car is jerking forward even if I just slightly press the throttle. It runs fine at idle, and when I rev it. It sounds beautiful. I know it's not the trans cause I can put it in park and rev it and it does the same thing and almost dies. I have no idea what else could be causing the problems.
Things I have replaced:
Dist. cap, coil, rotor, and plugs.
Fuel pump
Fuel filter
O2 sensor
My friend told me it could be the ignition timing, but then why would it run perfect at idle?
 
when a fuel tank is run to empty on an older car its not at all un-common for crud like fine rust to get pumped up thru the fuel rails and sediment finds its way into injectors,so getting them cleaned or replaced may be a good move, but before going to that expense, as a first step Id suggest, dropping back to basics and setting your ignition timing with a timing light,verifying your fuel pressure remains consistant,verify your battery voltage,check for vacuum leaks, and re-adjusting the TPS sensor and IAC
then carefully inspect the spark plugs
post clear pictures as the details are far easier to see if the pictures are clear
ALWAYS TEST ALL YOUR INJECTORS OHMS RESISTANCE, WITH A MULTI METER, IF YOUR ENGINE RUNS BADLY ,INDIVIDUALLY< THEY SHOULD ALL BE VERY CLOSE TO EQUAL, ANY THAT ARE NOT NEED TO BE REPLACED
READING THRU THESE LINKS AND SUB LINKS WILL HELP, YOU LOCATE THE CAUSE AND CORRECT IT

viewtopic.php?f=2&t=3074&p=8155&hilit=+software+cable#p8155

viewtopic.php?f=32&t=168

viewtopic.php?f=32&t=1401

viewtopic.php?f=70&t=202

viewtopic.php?f=55&t=1475&p=3325#p3325

viewtopic.php?f=55&t=1241

viewtopic.php?f=70&t=875

viewtopic.php?f=70&t=986

viewtopic.php?f=70&t=2798

viewtopic.php?f=50&t=609
 
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I have tested the fuel pressure at the schrader valve, and it's getting 39 psi. I did a vacuum check at the manifold, and everything seemed fine. Did the normal test of revving engine to 2k rm and dropping to check vacuum. Battery voltage is fine, I keep it on the charge regulator most of the time. I was going to reset the TPS and IAC valve tomorrow, but I have to work, so it's gonna be delayed even more. I replaced the spark plugs when I replaced all the distributor stuff. I did put some Lucas fuel injector cleaner in the tank, so that should have helped the injectors if they were clogged. And if they were clogged, why would it run so beautifully at idle and rev? What would you like pictures of?
 
If the car runs badly it should throw trouble codes , but you still need to check basics like the timing, valve adjustment,testing the fuel pressure, electrical connectors,vacuum lines, bad sensors etc.

if the injectors are partly clogged they could easily flow enough to allow the engine to idle yet not flow nearly enough to allow the engine to rev easily, under load,that may not be your problem but its certainly worth looking at,
after you reset the TPS and IAC
injector cleaners work great on varnish and fuel deposits...but on fine grit & crud like rust flakes ,sand, etc, not so much
Id like very clear pictures of the spark plugs labeled, per cylinder they came from, as a potential indicator of cylinder burn conditions, and pull codes, and read that set of linked info


READING THRU THESE LINKS AND SUB LINKS WILL HELP, YOU LOCATE THE CAUSE AND CORRECT IT

READ
viewtopic.php?f=2&t=3074&p=8155&hilit=+software+cable#p8155

viewtopic.php?f=32&t=168

viewtopic.php?f=32&t=1401

viewtopic.php?f=70&t=202

viewtopic.php?f=55&t=1241

viewtopic.php?f=70&t=875

viewtopic.php?f=70&t=986

viewtopic.php?f=70&t=2798

viewtopic.php?f=50&t=609
 
The car is not giving me any codes, and I will have pics of the plugs up later tonight. Unfortunately, I did not mark which cylinder they came from. I did get to thinking about what you said about the injectors, and you're right, it won't get rid of any rust particles that might be in them.
 
I finally figured out the problem! I took the car for another test drive today, and it gave me a code 44 again. That reminded me of something someone told me along time ago. They told me to drive the car with the fuel pressure gauge taped to the windshield. I did this, and when the car started running badly again, I noticed the fuel pressure was at 14 psi! I ohmed the injectors and they were all at around 17.3. I have replaced the fuel pump, and filter. The pump makes a very loud whining noise though.
 
yes the drop in fuel pressure, at the fuel rails from 39 psi to 14 psi is a sure way to get it to run like crap, its almost always a simple case of verifying the basics that leads to the solution, put a fuel pressure gauge on the fuel rail , and tape the gauge on the windshield so you can watch it when you drive

read thru the threads/links posted earlier ,start with these

http://members.shaw.ca/corvette86/FuelS ... gnosis.pdf

viewtopic.php?f=32&t=1401

I'm always glad to help out gentlemen!
most times, when youve got a problem with any car function, its just a matter of stepping thru all the potential sources of a problem, in a logical manor and verifying each potential problem source or eliminating it before stepping thru to the next.
obviously having a shop manual to refer to and a few tools to test with helps but the main factor is the logical process of verifying correct function , without guess work or assuming its correct without checking to actually verify it is correct.
example
I recently got a call from a buddy that built a killer 468 cubic inch 13.5:1 compression ratio, BIG BLOCK CHEVY with a very radical solid roller cam,
(crower 01521 cam/brodix heads)
(first solid roller cam he ever installed) and he spent hours trying to get it to idle below 1500rpm, it sounded like crap,and didn,t sound right, and he was sure the cam had lost a couple lobes, he called me over and we ran down a check list, I had printed out, when we got to the firing order question, he starting cursing and said, I can,t believe I spent 6 hours chasing this problem, when its my own damn stupidity!
(he installed a custom ground 4/7 swap cam and was still using the 1-8-4-3-6-5-7-2 firing order he had used for 30 years, without thinking and had verified it several times, not the 1-8-7-3-6-5-4-2 required by the new cam)

I had a different friend install a 467 cubic inch Pontiac V8 in a 1967 fire -bird and he hooked the headers to the stock 40 plus year old exhaust, the car ran decent up to about 4000rpm where it seemed to hit a wall on power, a simple check showed he had over 7 psi of back pressure at 4000rpm so the engine just could not fight that, swapping to a custom 3" dual exhaust with an (X) pipe really woke-up the power potential, and before testing he was convinced the cam was too mild, which it was not. (crower 60213 cam/ edelbrock 2957 intake/850 holley/edelbrock 60955 heads)

READ THE LINKS I POST YOULL LEARN A GOOD DEAL THAT WILL HELP IN THE FUTURE!
 
I would make sure you put the fuel filter facing the correct direction of flow, also if you changed it first before filling the tank back up, you could have blown all that crud into the new filter. Also a drop in pressure under load can be caused by A bad Pump, Check Valve or pulsator on the sending unit. I've heard stories of the older C4's having a small section of black rubber hose coming from the return line near the filler neck turning into jelly on the inside blocking flow. Also check your wiring harness to pump for corrosion its a common place for water to drip on, there is also a chassis grond there check for loose connection. Check for failing FPR by blocking off return line and looking at your fuel gauge to see if pressure holds. Pull the feed lines at the rail and do a fuel FLOW check. Also pull the vacuum line at the FPR and smell for fuel, if gas comes out replace FPR. Cold OHM checking the injectors wont tell you if they are clogged, but a loss of pressure that great smells like a blockage to me.Start with the most simplestuff first, It sounds like you've already started throwing parts at it, STOP, get your Field Service Manual and read it, and these forums, then follow the flowcharts and you'll save big $$, Happy Hunting! Keep us posted. ;)
 
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