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DTC 301 code

01-26-2010, 05:39 PM
I've been getting the code 301 which is misfire #1 cylinder. I pulled the #1 spark plug and wire. The plug was fine and the wire checked out fine. I cleared the code. 5 miles down the road the code sets again. So I inspected the ignition system from the coil to the spark plugs and found a severely corroded connection on the dist cap center connection and coil wire. I replaced the cap, rotor and spark plug wires and cleared the code. Two days and 30 miles later (yesterday) the code shows up again. This time I rebooted the computer by disconnecting the battery. I only drove the car to work (10 miles today) and no code yet. I don't feel like i've found the problem though. I need to make a 500 mile trip this weekend and i'm not feeling too good about it. Could this be an indication of the EGR passage plugging? Any thoughts you have would be helpful.

Thanks, Ron
97 1.0 137,000 miles

Johnny Mullet
01-26-2010, 08:03 PM
If you have spark and fuel an #1 is still missfiring, then you need to perform a compression test. Here is a guide..............

01-26-2010, 08:05 PM
Compression is fine. The problem is electrical.

Thanks, Ron

Johnny Mullet
01-26-2010, 08:11 PM
Compression is fine. The problem is electrical.

Thanks, Ron

You need spark, fuel, and compression for a cylinder to fire. Fuel is supplied to a 1.0 via throttle body, so if it runs, it's not fuel.

If you said the spark plug and wire is fine, then you have spark.

This means you do not have an "Electrical Problem" :nono:

Start the car, put on a glove, and remove wire #3. Is it sparking? Engine running really shitty? Repeat with #2 and finally #1. If removing #1 changes nothing, then either perform the compression test or throw parts at it.


01-26-2010, 08:32 PM
I'm telling you that the compression is fine. I did check it. Even the factory shop manual does not mention lack of compression as a cause for a DTC 301. The misfire is not caused by lack of fuel or compression. It must be electrical.

Johnny Mullet
01-26-2010, 08:42 PM
the factory shop manual does not mention lack of compression as a cause for a DTC 301. The misfire is not caused by lack of fuel or compression. It must be electrical.


Lemme know when you find your electrical problem.

01-27-2010, 12:16 AM
Your first post did not include spark plug replacement. Although your car could seem to run fine, the resistance across the air gap on spark plugs increases as your compression increases as in throttling up. A slight crack on the insulator of the plug can make high voltage go to ground before it reaches the end of the plug. To get that code it would not have to misfire 100% of the time, just a periodic miss that could go unnoticed could do it. Good luck.

01-27-2010, 07:40 PM
I replaced the plugs today just to eliminate them as a cause. The code came back within 30 miles of driving.

01-28-2010, 04:42 AM
That was the last thing left that could possibly be electrical. You've got a mechanical problem, most likely compression. Especially at that mileage, any G10 with 137K is suspect as far as burned valves go.

01-28-2010, 10:21 AM
The engine has about 60,000 miles since being rebuilt by me. Compression is 95-99 across the board cold. I've already said that compression is not the problem. It runs like there is nothing wrong. I'll have to check the gas mileage though to verify. EGR operates normally. Checked it yesterday. I'm starting to believe that there is no misfire even though the computer is indicating it. The PCM does not blink the check engine light first. It comes on solid and stores in memory. I'm going to check the wiring at the PCM today. Could be a loose or bad connection. The shop manual says that vacuum leaks, EGR, PCV, fuel pressure, defective crank timing belt pulley or poor connection at PCM could be the cause. That's alot of stuff... If I was able to collect freeze frame data when the code sets I would be better able to diagnose it. I don't have that kind of equipment. Evidently no one on this form has had this happen to them.

Johnny Mullet
01-28-2010, 09:20 PM
Minimum Compression allowable in your manual is 155 PSI.

01-29-2010, 05:23 AM
95 - 99 is a disaster, it's supposed to be 200 with 155 the factory recommended minimum, most cars will run down to about 100, but not well. You should certainly renew all electrical connectors and ground points, and check the timing belt lower pulley for make sure it's not slicing the woodruff key and walking around the crankshaft, but nothing that you've listed there would explain why it's reporting a cylinder 1 misfire rather than a general misfire.

Here's what my shop manual says, perhaps yours is missing an entire page on mechanical causes for this code:

Worn or faulty camshaft
Leaky or stick valves or rings
Excessive valve deposits
Weak valve springs
Malfunctioning Hydraulic valve adjusters
Incorrect valve timing
Intake (vacuum) leaks
Leaking head gasket
Loose or broken motor mount.

Yes, many of us have seen this problem, it's usually a bad spark plug wire or a burned valve.

01-29-2010, 10:47 AM
My bad. The compression is 195-199 cold. Forgot the 1. I took out the PCM yesterday. I saw no evidence of corrosion on the terminals. Removed and reinstalled the plugs several times. The code reset again at after about 50 miles. Cleared the code and left the reader plugged in while driving about 10 miles. I constantly checked for codes while driving. the 301 code would come up then go away then come up then go away while I was cruising. The light did not come on though. When the light has come on and I read the codes it always shows the code being set twice. Guess i'll have to check the crank gear for dirt. Probably tomorrow. Again the car runs fine and pulls as hard as it ever has. The plugs I replaced looked identical in color.

02-02-2010, 12:54 PM
Removed the crank position sensor and inspected the trigger plate etc. I found nothing wrong. Area is dry and clean. Checked wiring to the sensor plug and found nothing abnormal. Checked EGR valve and found nothing wrong. Checked for intake leaks visually. Nothing apparant. Test drive shows the same symptoms as before. 301 code still comes up occasionally and goes away while continuously checking for codes during driving. It can come up while cruising or stopped and idling. Engine light does not come on until misfire is detected twice. Again the car runs fine and pulls as hard as it ever has. Idle is good. I'm not sure what to do next.

03-03-2010, 12:24 PM
I may have found the problem. I was checking the EGR valve and solenoids IAW the service manual. The EGR vacuum solenoid resistance checks out ok. The blow test, according to the service manual, does not pass. When blowing air into tube A (#2 in the illustration) the air blows out of the filter not tube B (#1 in the illustration). When I connect 12 volts to the solenoid the valve shuts and does not let air pass through at all. The EGR valve and the other solenoid check out ok.

03-04-2010, 05:04 AM
EGR would not cause a misfire code, especially one for only one cylinder. EGR feeds into the intake manifold at the throttle body, how would it effect a single cylinder?

There are specific codes for EGR, the engine turns it on at a steady state cruise and watches the MAP sensor to see the change in intake manifold pressure. If stuck on, your engine would barely run, if stuck off it would run fine but an EGR code would be displayed.

03-04-2010, 03:09 PM
The factory service manual says that a malfunctioning EGR can cause this code. It also cites several other conditions, besides the obvious plugs, wires, cap, rotor and coil, as possible causes of this code.

03-05-2010, 05:10 AM
Good luck with it, I'm done. Everything that has been suggested has been totally rejected by you as a possibility, why ask a question and then not even consider the answers you get?:banghead::banghead::banghead:

03-05-2010, 07:12 PM
Rejected??? I already checked out all the possibilities all of you have suggested before I started this thread. The suggestions were not rejected. I found no abnormalities other than the corrosion on the distributor cap center post. I am an accomplished mechanic and have never had a problem finding and fixing situations like this. This one has me though. It is very frustrating. I'm going to replace the EGR solenoid this weekend. If that does not work then i'll know one more thing that is not the problem. I do appreciate all the input you all have given.

03-06-2010, 05:29 AM
Maybe you're not communicating that very well, or maybe I'm just a grumpy old coot. In retrospect, the second possibility is the most likely.


Johnny Mullet
03-06-2010, 07:38 AM
I still suspect a burnt valve.

03-15-2010, 05:50 PM
Well folks I replaced the EGR vacuum solenoid with a junk yard replacement. There was no change. Evidently the blow test in the manual is wrong. I also picked up a PCM out of a 98 or 2000 (not sure of the year) 1.0 and tried it. Not only did I get the 301 code but also got a 1401 code. Most likely the junk yard PCM is not compatible with the 97 sensor. I put the original PCM back in this morning. I also did another compression check followed up with adding oil and a second compression check. There was no difference between test 1 and 2. There is no compression problem as I stated earlier. No burnt valve and no broken valve springs. When I removed the plugs for the compression test and inspected them I found something. The plugs for cyl #2 and #3 are the usual coffee w/cream color. #1 plug looks like coffee w/alot of cream. Not white but slightly colored. These plugs have less than 200 miles on them so i'm not sure if I have a problem. The lighter #1 plug suggest to me that there may possibly be a slight intake leak. I'll have to check for a leak w/starting fluid. This problem has really kicked my butt. :disappoin

03-16-2010, 11:45 AM
Houston we've found the problem. :) Intake leak at the #1 cylinder/intake manifold gasket. Right at the outer most bolt. Using starting fluid to detect worked. Boy am I glad I found it. It is a very slight leak. Manifold vacuum at idle was within specs. Surprising that this leak would show up after 60,000 miles. I need to change the gasket to verify but this sounds promising. Wish me luck.

03-19-2010, 05:51 PM
:):):) The intake gasket was split about 1/8" causing the leak. I should have figured this out earlier since it only involved the #1 cylinder but was looking for the obvious problems thinking that a vacuum leak would only be in a hose. I must be getting old... I needed a tuneup and needed to change the coolant anyway. I'll put it back together tomorrow and verify. Thanks to everyone who provided input on this thread.


03-20-2010, 08:26 PM
I put the intake back on this morning with a new gasket. Problem solved.


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