Steady Rpm Cam Hop?

Dsum14 · Nov 10, 2015

I have a built 306, aluminum heads, Cam, Rockers, with a trickflow intake, exhaust, all the normal mods. I don't know the specifics on the motor because I bought it from a guy who had it in a 92 weekend drag car. When I got it, it ran very rich and had no power. I replaced the cap and rotor as they were burnt, new plugs and wires, american thunder cat back exhaust, and had it tuned. At that point, I started having a pretty violent hopping or jerking between 1800 and 2100 rpms. It did fine as long as I was giving it gas and accelerating, but if I were just trying to cruise at those rpms, I'd almost end up with whiplash. It definitely runs a lot better, but was burning very rich even after the tune. I found that the MAF wasn't calibrated to the 24lbs injector size. I switched out the MAF. It doesn't burn rich anymore and the hop seemed to get better, but it still does it. And sometimes it does it pretty bad. It's very annoying. I don't know if the tune had something to do with it or if because the MAF was wrong when it was tuned, that is causing the problem. Anybody have any suggestions?

jrichker · Nov 11, 2015

Fist of all, dump the codes, find and fix any code related problems.

Next AFTER you fix ALL the codes, save up your $$$ for a new custom dyno tune and chip.

Let's do the first step now...

Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on.

Dumping the computer diagnostic codes on 86-95 Mustangs

Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

Codes may be present even if the check engine light hasn’t come on, so be sure to check for them.

Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.

If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.

The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

Your 86-88 5.0 won't have a working Check Engine Light, so you'll need a test light.
See AutoZone Part Number: 25886 , $10

Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

Or for a nicer scanner see Equus Digital Ford Code Reader (3145) Equus - Digital Ford Code Reader 3145.
It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $22-$36.

Dsum14 · Nov 11, 2015

That's very detailed, thank you. It does have a light on and has to do with the EGR. It does have an SCT Chip in it and was dyno tuned, but that was before I knew the MAF didn't match the injector size. When they tuned it, they assumed the MAF was matched. I don't know if that makes a difference or if I need to go back and have it tuned again...

TOOLOW91 · Nov 11, 2015

If it has a decent size cam and stock gears this may be the issue

Sent from my iPhone using my fingers while my auto correct makes me seem illiterate

Dsum14 · Nov 11, 2015

Rear end has 3.73s. Cleared codes and took it for a drive. Got a 511 electronic control assembly read Only memory and a continuous code of 332 insufficient egr flow.

jrichker · Nov 12, 2015

Dsum14 said:
Rear end has 3.73s. Cleared codes and took it for a drive. Got a 511 electronic control assembly read Only memory and a continuous code of 332 insufficient egr flow.

The 511 code is probably due to the presence of the SCT chip. I would not worry about that code at this time.

If the EGR sensor or vacuum line has been removed, disconnected or otherwise mangled, it will set the 332 code.That should have little or no effect on your current problem

Here's the same code for an 86-93 5.0 Mustang. The function is the same but the wire colors may be different.

Code 33 - Insufficient EGR flow detected.
Look for vacuum leaks, cracked vacuum lines, failed EGR vacuum regulator. Check to see if you have 10” of vacuum at the EGR vacuum connection coming from the intake manifold. Look for electrical signal at the vacuum regulator solenoid valves located on the rear of the passenger side wheel well. Using a test light across the electrical connector, it should flicker as the electrical signal changes. Remember that the computer does not source any power, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

See Mustang FAQ - Wiring & Engine Info for some help with the diagrams.

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 or see the EGR test jig drawing below. Connnect the test jig or to directly to manifold vacuum.

Do not connect the EGR test jig to the EVR (Electronic Vacuum Regulator).

apply 5in vacuum to the valve. Using the test jig, use your finger to vary the vacuum

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 EGR test jig to the hose coming off of the EGR Valve.
Use your finger to cap the open port on the vacuum tee.
snap throttle to 2500 RPM (remember snap the throttle don't hold it there).
did the vacuum gauge show about 2-5 in vacuum?
if not the EVR has failed

EGR test jig

The operation of the EGR vacuum regulator can be checked by using a test light applied across the wiring connector. Jumper the computer into self test mode and turn the key on but do not start the engine. You will hear all the actuators (including the EVR vacuum regulator) cycle. Watch for the light to flicker: that means the computer has signaled the EGR vacuum regulator successfully.

Dsum14 · Nov 12, 2015

Okay, so neither code has anything to do with my problem. I contacted the guy who tuned my car and he said they can shut off the 332 code and it's probably being tripped because my egr bypass is capped at the headers. He says the 511 shouldn't make the light come on...is that accurate? He also told me that since my maf wasn't matched at the time we tuned it last time, it is probably running very lean and causing my hop issue. His suggestion to fix it, is to bring it back in to be tuned again. I guess $300 for a new tune isn't that bad of a fix.

mikestang63 · Nov 12, 2015

Dsum14 said:
Okay, so neither code has anything to do with my problem. I contacted the guy who tuned my car and he said they can shut off the 332 code and it's probably being tripped because my egr bypass is capped at the headers. He says the 511 shouldn't make the light come on...is that accurate? He also told me that since my maf wasn't matched at the time we tuned it last time, it is probably running very lean and causing my hop issue. His suggestion to fix it, is to bring it back in to be tuned again. I guess $300 for a new tune isn't that bad of a fix.

im wondering why they didnt adjust the tune for the mismatched MAF? Any competent tuner should know how to do this. I would be asking him why is he charging you for another tune when he should have seen this the first time.

Dsum14 · Nov 13, 2015

I know he was assuming the MAF matched, but are you saying that the tuner should have recognized that it was mismatched? I talked to a second tuner who also told me I would need to have it retuned now that I have the right MAF.
I spoke to a buddy of mine who has a 331 stroker. He said he has the same cam hop issue and had always been told that the hop was caused by the bigger cam that makes power in the higher rpm range. But he said he has a trickflow stage 2 and another buddy has the same hop issue and is running the trickflow stage 1 cam.
Since I didn't build my motor and rather bought it from someone who had it built, I do not know the specs on the cam.

mikestang63 · Nov 13, 2015

Dsum14 said:
I know he was assuming the MAF matched, but are you saying that the tuner should have recognized that it was mismatched? I talked to a second tuner who also told me I would need to have it retuned now that I have the right MAF.
I spoke to a buddy of mine who has a 331 stroker. He said he has the same cam hop issue and had always been told that the hop was caused by the bigger cam that makes power in the higher rpm range. But he said he has a trickflow stage 2 and another buddy has the same hop issue and is running the trickflow stage 1 cam.
Since I didn't build my motor and rather bought it from someone who had it built, I do not know the specs on the cam.

yes- the tuner should have noticed the mismatched MAF.

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