Posted: May 10 2008 at 7:22pm | IP Logged

I recently bought a 1998 Frontier with the four cylinder 2.4 engine and automatic transmission.  I really like the truck but when I bought it the engine rolled over but would not run.

I bought the truck with 139,000 miles on it and knew that the engine had been driven by an older woman who had her on the expressway and she just shut off one day as she pulled into a rest stop...

After pulling her apart I found a cylinder head with all 16 valves bent.  Sooooo, I did the right thing, bought a book, and a head and all of the tensioners and timing chain components and gaskets.

Put her back together and I'm having a problem...

- She idles really well but won't accelerate past 3000 rpms.  I can sit in the driveway and she will sit there and idle but when I hit the gas its like....whaw, whaw...or that sound you get in a carb car when the accelerator pump doesn't work.  If I'm really easy on the pedal (1/4") or so she will rev to no more then 3000 rpms and then if I try to "barely" push her any more at all....whaw, whawww, and back to idle. 

- If I lether sit and idle, no problems, when I put the accelerator to the floor and try to rev her up...(yes I did say to the floor), she will rev no higher then 2-3K and just sit there.  She never reaches the rev limiter but sits at a steady 2-3K rpms and whaaaw.

- I'm thinking it may be fuel related or something...is there some device that acts like an accelertor pump of sorts and skirts extra gas or allows the injectors to squirt more???

- Here are the only peculiar things that happened during the teardown and build.

Timing the thing:  This vehicle was different then any I had done before her.  I simply installed the crankpulley and rotated her around to TDC (as close as I could with a long screwdriver into the number one spark plug hole) and then noticed the crank gear dot was at about the 3 to 4 - O'Clock position if I can remember right. I placed the silver tooth on the chain there at the dot and then put the chain on the idler pulley and aligned the other silver link with the dot on the idler pulley gear as instructed in the book.  I then put the bottom tenstioner and guides on and was finished on the bottom.  The top chain was just as easy as the three silver links were placed on the cams in the following orientation:

- The left and right cam gears seemed the same and when they were installed the keyway was up on both cams and the cam gears had what I called a left side and a right side mark in there 10 and 2pm teeth.  The left gear was to have a silver link at the 10:00 mark and the right gear had a silver tooth at the 2pm spot.  The bottom of the top chain had a silver tooth that was to be alligned with the bottom dot on the idler gear.  After all of this I placed the top tensioner in place and knew I had done the best I could...

Oil pump installation:   

I wish I could get my hands on the idiot that designed a distributor shaft with its gear on the oil pump and not on the end of the distributor... Well, that is another story. Sufice it to say, I had a time but finally was able to allign the dots on the oil pump body and the shaft so that when the two were placed in the engine my distributor alligned with the number one spark plug tower at TDC of the engine.

The only other thing that happened that I feel must be said is that when we were wrestling with the intake manifold (wasn't removed from the engine and nothing was disconnected) and trying to get it alligned with the head we noticed a gas smell.  The battery was out and we had thought that maybe we broke something but never found anything.  The fuel pump had never ran as we noticed after not having fuel pressure upon start up that the dealer or someone had for some reason removed the fuel pump fuse.  Once we replaced that the engine started right up but still runs with no power at all and won't rev past 3K rpm.

Is it possible that I have the timing chains on wrong (it purrs like a kitten below 1000 rpm)?

It is also very hard to start when warmed up, but starts when you breath on the key when it is cold.  I also noticed when I took the spark plugs out to check their gap that they were black and a bit sooty after being installed new.  My son also noticed black smoke out the tail pipe at times.  Could it be a fuel pressure regulator?  Why does it idle so well then? but won't scream to top end?

Thanks for any advice you may have and sorry for such a long disertation but wanted you guys to know all the things that led to the problem.  Car sat no longer then 2 months after breakdown.

Mr. Tripp

Augusta, GA

Posted: May 11 2008 at 10:37am | IP Logged

Going to try and leave this in bullets so it is easier to follow:

- Thanks for the PO300 and that should go away when I find the problem.

- Plugs were new when inserted and gapped to 0.040 which is between the 0.038 and 0.043 recommended.

- Don't think it is the wires as they look like new and truck was running just fine when it broke down on the expressway.

- I too am thinking timing but....want to think it is impossible....

Your drawing shows the upper timing relationship and the drawing is bad.  There are 7 teeth between each link and that is the way (drawing) that I installed the upper chain.  The bright silver teeth went on the intake cam with the link at 10pm or so and the exh cam's link was at the 2pm as shown.  The bottom silver link for the upper chain located on the intermediate shaft was at the 5:30 to 6pm possition as shown.

As for the lower chain the engine was rotated with a long screwdriver in the number one hole and when the tool reached its highest point the crank gear was in the indicated position with the keyway pointing towards 11pm as the silver dot / link was placed on the crank gear at the 4pm position.  This left the 2nd silver link on the idler sprocket in the 2pm position as my book shows.

- The upper chain has 3 silver links with 7 teeth inbetween each link. Installation is easy as you can't get it wrong.  (In my humble opinion..ha)

- the lower chain has only 2 silver links and for both of them to be at the above described position it too is impossible to get wrong.  The only way would be to some how have the idler link at a position other then 2pm which would be way out of time and the upper chain wouldn't go on as it did with the bottom link lining up with the dot on the bottom of the idler sprocket.

- It is for these reasons that I say I don't like the set up and allignment but you have to hand it to them...it all must be right or it all will be wrong.

- Timing...I was able to put a timing light on it and after getting the oil pump and shaft in right the timing is set to 20 degrees BTDC when it runs best at idle. 

- Fuel filter?  Will this let it idle but not accelerate?  If so then it is a possibility but why can I sit there at 800rpm and slowly accelerate to 3k but can blip it to 3k?

- Mass air flow?  That is right on the side of the carb and has input to the PCM right?  Something is either flooding it or starving it or not sending the right information to the injectors???  I'm surprised that I am not getting another code.

Thanks a ton for you help and if you would like to talk please leave me your number and I can call you or call me at (706)825-7180 in Augusta, GA.

Thanks again!

Mr. Tripp

Posted: May 11 2008 at 3:07pm | IP Logged

I was able to go out and tinker a bit with it after we talked.  This is what happened.

I found tha the Throttle Body had a hole in it just above the MAF which is mounted on the outside of the Throttle Body.  I plugged it with my finger and had my son start her up...she started right up and varoom, varoom I was able to flip the throttle and she sounded great as I was able to rev her up for 4-5 seconds or so..."Yep, I found the problem, or so I thought..."  Just as fast as she sounded fine, she went right back to doing what she was doing.  I couldn't get her to repeat the same again.  So then I took the MAF out and tried to clean it and install it and still no luck.  I will buy one just the same. 

Then I took the EGR off and noticed that I could blow into the EGR pipe and the air I was blowing (simulating exhaust pressure on the valve) was getting past the valve.  If I blew a force of 10 then 3-4 of it was getting by the valve.  I pulled up with my fingers on the diaphram and also sucked it up with vacume and it worked fine. But it does have a leak and I'm going to replace it too.

I'm thinking the MAF sensor and the EGR replaced might fix it.  There are no other codes being set but the crank sensor setting the misfire detected code.  Many of the emissions sensors send outputs for timing, and fuel metering....the MAM is said to cause many a driveability problem so that is what I hope it is.

Thanks!

Mr. Tripp