Popping through intake, bucking, missing... major FI problem like I have never seen.

[Slow LX]

This is my first post in a long time, howdy! I will cut to the chase....
I recently placed a 1988 302 with fresh Trickflow Heads, Intake, and Lunati 51014 Cam (installed -4') 5 speed, etc... In a 1993 Ford Ranger Splash.
I am having horrible drivability problems. It is a Mass air, newer motorsport harness, A9L… It runs horrible when cold. You can hold the pedal at half throttle and it pops through the intake and does not rev for at least 5-7 seconds, just keeps popping. After 3-4 minutes of driving it clears out and drivers pretty good. Pretty smooth through the rpms, but does miss once or twice. At the same point, about 5 miles from my house it goes bizerk. I mean bad. It starts bucking, popping through the intake every time you let off the throttle and try to accelerate again. It does this at the same point in the trip every time. It is like a light switch.
However, if you press the pedal passed ½ or more it will run better, it misses once or twice, but nothing like what it does at light throttle. When I unplug the Mass air meter it runs sooo much worse. I mean, it can barely make it up the driveway. You can push the throttle to ¾ and it does not even rev, it just coughs and pops through the intake.
I pulled codes and got 91 41 O2’s lean, not switching and some thermactor (81 84 85) stuff and (nds) stuff. I unplugged the 02’s and still runs bad. I checked the wiring to the computer and I am getting continuity to the proper computer pins from the plugs at the exhaust. The o2’s look new but I had them lying around for a while. I am in the process of hooking up the Wideband O2 to see what is happening. I get a misfire from #4 when I put the timing light on that wire and drive it. Timing is at 12’ and advances nicely to 35-36 when you rev with the spout in… It also runs really bad when you pull the spout. It will barely drive until you almost floor it, and then it clears out and goes.

My question is, when the o2’s are unplugged and the mass air meter is unplugged what is causing the truck to run so poorly? It should be running off preset tables in the computer, right? I can press the throttle and it chokes and pops.

I have the egr propped half way open, still plugged in, Tps is Good, full sweep smoothly… I am going to check for the voltage at the computer plug when the truck is running for the o2’s, tps, maf, … I have switched out 2 computers, 2 maf, 2 TPS sensors, 2 set of plugs, 2 sets of plug wires, 2 distributor’s (MSD currently), 2 coils…etc

I just put in a 255 in tank pump, did it with the old pump also, fuel filter, even took the fuel rails off and cleaned the injectors/ changed the f/p reg...

I am going crazy here...

 

[89streetbeast]

sounds like a timing problem. didnt get the firing order messed up did ya ?

 

[txstang84]

EGR propped open will have a definite nasty effect, EGR is only supposed to operate at part throttle cruise or accel...if it's open at idle, it will most certainly run like crap.

Also, yes, the computer will run from preset tables, but if it has no basis to run them (learned memory) it will think that it's operating with a stock 302, not a cammed, and headed engine. Not to mention, "limp home" mode is not at all friendly, it'll run...but just barely. Timing does sound like a culprit though, especially if you're not getting any real response below 1/2 throttle.

Dump the computer, reconnect all your sensors, ck your timing again, and ck your MAF wires for contamination.

Other suggestions guys??

 

[superhuaman]

yes check timing with spout out. what is fuel pressure? also, it sounds like it is running too rich. the computer thinks it is too lean, thus setting a code, but also trying to add more fuel.

 

[HISSIN50]

I think he means he has the EGR position sensor set halfway in (simply let us know if you have a functional EGR on the truck).

A cylinder balance test is a nice way to confirm that #4 has an issue and see if any other cylinders are not contributing (as opposed to a tune-induced or random misfire). I'd not expect the car to run too hot with the MAF disconnected (O2's can be more lenient). Do you have a means of tuning it (read a TwEECER)? If so, geting it to idle in OL might help. Also, what size squirters are you running?

That was a huge opening post so it might take a bit to whittle the issue down.

Good luck.

 

[Slow LX]

I do have the egr plugged in but the valve propped open. I do not have the egr spacer in between the throttle body and intake anymore. I have unplugged the egr and drove with no good result.

I have tried setting the timing to 36' with the spout out, locking it a 36', and took it for a ride. It ran pretty good until it got to this one spot a few miles down the road and like a light switch, bam, it ran horribly again.

1-3-7-2-6-5-4-8- firing order check more than a couple times...


I am in the proccess of putting the wideband and the fuel pressure gauge in.

It will not do a koer test, I think because of the nds switch. I will have to try with the clutch pressed in...

I also got the code for the fuel pump signal to the computer not registering...

Thanks for the ideas guys, I will keep you posted...

I really want to get this straightened out...

 

[HISSIN50]

Wow, the EGR valve itself is being held open? The other guys were right. I'm not sure why this was done, but I'd undo it.

36* locked timing is a lot - I'd try 26* for right now and see how it does (it's more of a middle of the road timing setting).

 

[EMW150]

It could be a connection. My '87 acted up like that till I found a connector not getting good contact. I don't think it's a timing issue or firing order since it acts up intermittantly. If it was timing or firing order it would be all the time.

 

[jrichker]

Backfiring
Backfiring out the intake is either a valve stuck open, a lean mixture or spark plug wire(s) connected to the wrong cylinder(s). Check compression on all cylinders and then look for vacuum hoses loose, cracked, misconnected. Check the line for the vapor recirculation system – it is easy to knock loose and not see it when you connect the air pump plumbing. If the vacuum line for the EGR valve and the air pump are cross connected, some very strange things can happen. Check the mass air flow electrical connection and see that it is tight, the same goes for the fuel injection wiring harness connectors up on top of the manifold near the firewall.

Sticking valves: If a intake valve is bent, has a bad spring or is misadjusted, the engine will sometimes backfire through the intake. Use a vacuum gauge connected to any convenient spot on the intake manifold. Run the engine at 1000 RPM & look for 18-21 inches of vacuum with a steady needle. A problem intake valve will make the vacuum gauge needle sweep 5-10 inches .

Lean fuel mixture breaks out into several sub categories:
A.). Vacuum leaks
B.) Air entering the intake without passing through the MAF.
C.) Failure of the MAF, BAP/MAP (Baro or Manifold Air Pressure, same sensor, different name), ACT (air charge temp), or ECT (engine coolant temp). These should set a code in the computer.
D.) Leaking exhaust gases from EGR valve at WOT, or EGR opening when it should not be open.
E.) Poor fuel delivery due to bad fuel pump, clogged filter or bad fuel pump wiring. Look for low pressure or fluctuating pressure. Standard injector pressure is 39 PSI at idle, with the vacuum line disconnected from the regulator and capped.
F.) Clogged fuel injectors.- see the cylinder balance test below
H.) Fuel injector wiring problems causing injector not to deliver rated flow.
I.) Computer problems: (computer problems are not common like sensor problems)
J.). ROM has bad data in fuel or timing table. This should also set a code in the computer.
K.) Failure of one or more of the computer's driver transistors for the fuel injectors. No code set on this one. Use a noid test light to test the injector wiring & injector drivers,
L.) MAF calibration off or mismatched to injectors.
M.) ACT or ECT bad. Sometimes the sensors will be off calibration, but not bad enough to set a code. If they falsely read too high a temp, the engine will back off fuel delivery.

Cylinder balance test:
Warm the car's engine up to normal operating temperature. Use a jumper wire or paper clip to put the computer into test mode. Start the engine and let it go through the normal diagnostic tests, then quickly press the throttle to the floor. The engine RPM should exceed 2500 RPM's for a brief second. The engine RPM's will increase to about 1450-1600 RPM and hold steady. The engine will shut off power to each injector, one at a time. When it has sequenced through all 8 injectors, it will flash 9 for everything OK, or the number of the failing cylinder such as 2 for cylinder #2. Quickly pressing the throttle again up to 2500 RPM’s will cause the test to re-run with smaller qualifying figures. Do it a third time, and if the same cylinder shows up, the cylinder is weak and isn’t putting out power like it should. See the Chilton’s Shop manual for the complete test procedure.

EGR operation
Some basic theory to clarify how things work is in order…

The EGR shuts off at Wide Open Throttle (WOT), so it has minimal effect on performance. The addition of exhaust gas drops combustion temperature, increases gas mileage and reduces the tendency of the engine to ping. It can also reduce HC emissions by reducing fuel consumption. The primary result of EGR usage is a reduction in NOx emissions.

The EGR system has a vacuum source (line from the intake manifold) that goes to the EVR, computer operated electronic vacuum regulator. The EVR is located on the back of the passenger side shock strut tower. The computer uses RPM, Load. and some other factors to tell the EVR to pass vacuum to open the EGR valve. The EGR valve and the passages in the heads and intake manifold route exhaust gas to the EGR spacer (throttle body spacer). The EGR sensor tells the computer how far the EGR valve is open. Then computer adjusts the signal sent to the EVR to hold, increase or decrease the vacuum. The computer adds spark advance to compensate for the recirculated gases and the slower rate they burn at.

There should be no vacuum at the EGR valve when at idle. If there is, the EVR (electronic vacuum regulator) mounted on the backside of the passenger side wheelwell is suspect. Check the vacuum line plumbing to make sure the previous owner didn’t cross the vacuum lines.

Diagram courtesy of Tmoss & Stang&2birds.

The EGR sensor is basically a variable resistor, like the volume control on a radio. One end is 5 volt VREF power from the computer (red/orange wire). One end is computer signal ground (black/white), and the middle wire (brown/lt green) is the signal output from the EGR sensor. It is designed to always have some small voltage output from it anytime the ignition switch is the Run position. That way the computer knows the sensor & the wiring is OK. No voltage on computer pin 27 (brown/lt green wire) and the computer thinks the sensor is bad or the wire is broken and sets code 31. The voltage output can range from approximately .6-.85 volt.


EGR test procedure courtesy of cjones

to check the EGR valve:
bring the engine to normal temp.
connect a vacuum pump to the EGR Valve
apply 5in vacuum to the valve.
if engine stumbled or died then EGR Valve and passage(there is a passageway through the heads and intake) are good.
if engine did NOT stumble or die then either the EGR Valve is bad and/or the passage is blocked.
if engine stumbled, connect vacuum gauge to the hose coming off of the EGR Valve
snap throttle to 2500 RPM (remember snap the throttle don't hold it there).
did the vacuum gauge show about 5in vacuum?

if not, check for manifold vacuum at the EGR vacuum valve.
if you have manifold vacuum then connect vacuum gauge to the EGR valve side of the vacuum valve and snap throttle to 2500 RPM.
should read about 5in vacuum

Code 41 or 91 - O2 indicates system lean. Look for a vacuum leak or failing O2 sensor.

The computer sees a lean mixture signal coming from the O2 sensors and tries to compensate by adding more fuel. Many times the end result is an engine that runs pig rich and stinks of unburned fuel.

The following is a Quote from Charles O. Probst, Ford fuel Injection & Electronic Engine control:
"When the mixture is lean, the exhaust gas has oxygen, about the same amount as the ambient air. So the sensor will generate less than 400 Millivolts. Remember lean = less voltage.

When the mixture is rich, there's less oxygen in the exhaust than in the ambient air , so voltage is generated between the two sides of the tip. The voltage is greater than 600 millivolts. Remember rich = more voltage.

Here's a tip: the newer the sensor, the more the voltage changes, swinging from as low as 0.1 volt to as much as 0.9 volt. As an oxygen sensor ages, the voltage changes get smaller and slower - the voltage change lags behind the change in exhaust gas oxygen.

Because the oxygen sensor generates its own voltage, never apply voltage and never measure resistance of the sensor circuit. To measure voltage signals, use an analog voltmeter with a high input impedance, at least 10 megohms. Remember, a digital voltmeter will average a changing voltage." End Quote

Measuring the O2 sensor voltage at the computer will give you a good idea of how well they are working. You'll have to pull the passenger side kick panel off to gain access to the computer connector. Remove the plastic wiring cover to get to the back side of the wiring. Use a safety pin or paper clip to probe the connections from the rear. The computer pins are 29 (LH O2 with a dark green/pink wire) and 43 (RH O2 with a dark blue/pink wire). Use the ground next to the computer to ground the voltmeter.

Most of the common multimeters have a resistance scale. Be sure the O2 sensors are disconnected and measure the resistance from the O2 sensor body harness to the pins on the computer.

Note that all resistance tests must be done with power off. Measuring resistance with a circuit powered on will give false readings and possibly damage the meter. Do not attempt to measure the resistance of the O2 sensors, it may damage them.

The O2 sensor ground (orange wire with a ring terminal on it) is in the wiring harness for the fuel injection wiring. I grounded mine to one of the intake manifold bolts

Replace the O2 sensors in pairs if replacement is indicated. If one is weak or bad, the other one probably isn't far behind.

 

[seijirou]

Unprop that EGR valve first, there's no reason for it to be half open. plugged in or unplugged doesn't matter if it's half open, it will suck exhaust gasses either way as that's a mechanical function not electronic.

If you've got a miss on #4, make sure that it's not arcing in the cap or somewhere else and causing a different plug to fire at the wrong time. That can give you some really odd behavior that could be intermittant.

 

[Slow LX]

Thanks for all of your input guys.

I do not have any pollution equipment on the truck. I have a vacuum gauge on the truck and it reads 5-6 inches at idle, it is 4' retarted but when you rev it it will pull 20-22 and smooth right out. My engine builder saw the truck run and he said it sound mechanically sound. He re-valved, new guides , etc in the trick flow heads etc...

I t runs the poorest with the mass air unplugged as of right now....

This weekend I am going to see what the voltage is at the computer plug for all of the sensor signal wires.

 

[88-5.0mustang]

5-6 seems extremly low... id guess u got a vacuum leak.. stock 302s make about 16 inches and my car which is similiar setup but with abit more duration makes about 12in of merc

 

[txstang84]

5-6 seems extremly low... id guess u got a vacuum leak.. stock 302s make about 16 inches and my car which is similiar setup but with abit more duration makes about 12in of merc

No doubt...before I put on my blower, I'd pull about 14-16" hg depending on where I put the timing. But, now with the blower, it only pulls about 8-10" hg.

 

[seijirou]

Thanks for all of your input guys.

I do not have any pollution equipment on the truck. I have a vacuum gauge on the truck and it reads 5-6 inches at idle, it is 4' retarted but when you rev it it will pull 20-22 and smooth right out. My engine builder saw the truck run and he said it sound mechanically sound. He re-valved, new guides , etc in the trick flow heads etc...

I t runs the poorest with the mass air unplugged as of right now....

This weekend I am going to see what the voltage is at the computer plug for all of the sensor signal wires.

Why is the timing backed so far out? You should be in the 30's when you give it some gas. Try giving it 8-10 degrees of base advance. I thought you said the EGR was propped half open, but now you're saying there's no smog equipment?

The vac you're pulling is way low too, but retarded timing will do that.

 

[dragnazz5.0]

youre getting such low vacuum readings because of the egr being open. its essentially a vacuum leak at this point

 

[Slow LX]

I do not have the egr on the intake, it is just mounted in the engine bay hidden being held open via a aluminum piece I made. I could not fit the egr spacer between the throttle body and intake due to the air conditioning.

I probed the wires going to the 60 pin harness at the computer with the engine running(pulling 5-6" hg). I can make the truck pop and miss when I try to read the pin #50 voltage on the .25 volt scale on my analog meter.
However, when I try to read it on the 10 volt scale it will not effect the way it runs at all, and reads 1 volt at idle and when reving to 2500rpm or so, it will sweep up to 2 volts.

I also read the O2's at the computer(41-91 codes). On the .25 volt scale they would barely move.

This is where it gets wierd, after doing all of this the idle raised 500 rpm or so, and it was pulling 12"hg of vacuum. I later drove the truck home and it ran great! No bucking missing, poping or anything. The coolant temp also got higher. It was at 1/2 way up instead of usual 1/4 way up.
This is what I found, maybe somebody can see something here:

pin 43-Left O2= KOEO= 0 volts / KOER= full sweep across .25 volt scale(changed as the motor warmed up and ran right). When it was not running right, it would barely move on the .25 volt scale.

pin 29-rght O2= KOEO= 0 volts / KOER= full sweep across .25 volt scale(changed as the motor warmed up and ran right). When it was not running right, it would barely move on the .25 volt scale.


pin 50-MAF = KOEO= (6/50) 6th line on the scale of 50 lines.(.25 volt scale on meter).
Unplugged= 1 volt / KOER= 1 volt at idle. (Try to read on the .25 volt scale it will pop the same exact way it does when it is not running right pulling 5-6"hg vacuum) would sweep up to 2 volts as it was reved lightly to 2500 or so.

pin 9-MAF rtrn= KOEO= (5/50) 5th line on the scale of 50 lines.(.25 volt scale on meter).
KOER= (11-13/50) swept lightly on idle, 11 through 13 lines on the scale of 50 lines.(.25 volt scale on meter).

When I unplugged the mass air at the meter, it read 5 volts

pin 19 fuel pump monitor= 12 volts when running. Got a code for that do not know why?

pin 7- Engine collant temp= KOEO (cold 70'F) 3 volts. Unplugged from the heater rail read 4 volts. It eventually read 1 volt when warm.

Pin 47- TPS= KOEO= 4.5 volts / KOER= 4.5 volts

Pin 46- TPS= signal = KOEO=1 volt / KOER= 1 volt SWept nicely as revved, but when I open the throttle all the way it will only reach 3.75 to 4.0 volts... At both the computer and the sensor it's self.

pin 26- tps= KOEO= 4.5 volts / KOER= 4.5 volts.


pin 27- EGR signal- KOEO=1 volt / KOER= 1 volt


I got it to run great for 15 minutes or so, but after a while it was like a light switch, it just went back to it's horrible drivability...

 

[superhuaman]

It sounds like it is running lean, because the computer sees the EGR being open, and subtracts fuel to compensate. EGR gases displace air, richening the mixture. Therefore, the computer thinks the engine is running too rich, and leans it out. You need to remove the thing you have in there to hold the valve open. Try running it with the EGR unplugged. It will set a code, but it might run better. If that fixes it, then get a $15 EGR Eliminator from ebay to turn out the engine light, if it comes on.

 

[jrichker]

The odd behavior when measuring the voltages is an indication of a multimeter not being correctly set or loading the circuit. High quality multimeters & DVMs have a very high input resistance to prevent loading of the circuit that could change circuit operation. Pin 50 is the MAF signal, which if loaded to the point where the voltage drops, will negatively affect engine operation.

I believe what you are telling us about the EGR is that you have it mounted in the engine bay so that you can connect the electrical and vacuum connections. Is that correct? If so, disconnect the vacuum line and the electrical connection while you troubleshoot the problem. Be sure that you plug the disconnected vacuum line. You will set code 32 or 33, but that will not prevent the engine from running smoothly.

Set the timing at 10 degrees BTDC and redo the vacuum tests. If you do not pull at least 14" of vacuum at 650-725 RPM, you have a vacuum leak. That would explain the 41/91 code.

 

[Slow LX]

Well, I had 2 mass air meters laying around....

Ran like ape S*&% with both meters I had....


Tried a mass air meter from a friends car, his car was know to run fine...

Guess what - it is like a new truck:

it idles at like 1,800rpms...

18-20"hg of vacuum...

It has the drivability of a stock mustang!

I just hope this stays running this well!!!

Oh yeah, this thing is a rocketship!!! Now I can put in my 42# and hook up the dry shot!

Thanks for all your help guys, hopefully I will not be posting on this thread anymore!

 

[Supaman]

did you get any code when you had the other 2 mass air meters on? I was just wondering because my car is almost running the sme way and it's not throwing any codes. Glad you got your problem solved.