Atx to mtx conversion wont rev past 5k

[Jon Klein]

Hey guys this one is unique. Car is a 1994 original atx. Swapped to mtx keeping the atx harness and 3.2. MLPS soldered as per instructions. Car has sho shop catless y pipe, big bore secondaries, and ported runners. Car starts perfectly and runs awesome every day. Been driving like this every day for 3 years and now im sick of it. When you jump on it the car runs perfect till about 5k then starts to drastically run out of power almost struggling to get past 6k. Feels like fuel cause the less pedal u give it the better it revs. Also, somtimes it feels like it hits a rev limiter at 5500rpm if you have it floored. Does this at any speed. Will free rev to 7k in neutral (mtx now) done plugs and wires... with factory parts. Fresh 60k minus crank sensor. Will try to update soon woth codes that matter... becsuse there are many since the trans is missing lol. Also, i just noticed that the DPFE sensor is no longer there, same with egr since when they swaped it they used a MTX intake manifold. Would that be the cause? Almost feels like when u hit the 144 mph fuel cut at the same rpm in 4th gear on an atx. There is a speed sensor in the car and hooked up to the atx harness. I did not do the swap. I owned the car as an atx. Sold it to a friend who did the swap... and then got it back when i couldnt stand him destroying a beautiful opal frost in mint shape because he never cleaned or cared for the car the way it deserved. Please help. Thanks guys..

 

[rubydist]

the atx pcm has a 4000 rpm rev limiter in neutral. so, if you were not successful at the modification to tell the pcm that the car is not in neutral, that is why it is not revving up as desired.

 

[Jon Klein]

It revs past 4k. Without doubt. Its def 5k. And its not a rev limit all the time. Most times it just struggles to rev past 5k but will if you force it... just has no power

 

[Jon Klein]

It also is more pronounced floored than if you lift when it starts to happen and feather the pedal to get more rpm. And other then that runs awesome and has all its power up to the 5-5.5k point.

 

[Jon Klein]

Btw ruby thanks for the reply. Ive been on the forum since 02 when i got my first SHO at the age of 16. You, bob gervais, toolman.... all the OG posters will forever be my heros..

 

[SHOdded]

Sticking butterfly actuators?

 

[Jon Klein]

The secondaries open beautifully at 4k rpm everytime.... great burst of power and that awesome sound. This really feels like fuel... or timing... its too rythmic and precise to be a random event. Thanks for the reply SHOdded!

 

[Jon Klein]

Also the secondaries both open when car is off, and close when started... they also open when revved to 4k stationary and moving... and will stay open to 7k when free revved in neutral. (Rememebr the car is a mtx now)

 

[Jon Klein]

Im going to try to post a video later this evening...

 

[SHOdded]

Usually with fuel, you will see problems with the fuel pump or fuel pump regulator. If the vehicle has been sitting awhile, it is gummed up injectors/filter. Also not uncommon are EVAP issues due to stuck check valve, which most people end up simply eliminating.

Timing - many options to go wrong other than just behind the timing cover. Mainly grounds, and DIS-related issues. Any time you take off the manifold, there is potential for DIS issues - insufficient grease on the backside, cracked connectors, and again, ground. I do not think this is ground related, but could be an overheating DIS module.

I am not intimately familiar with this conversion, but is an EGR system still active & present? Any chance the DPFE module is at fault? Clogged EGR passages ("nostrils") come to mind.

What spark plugs are you using?

 

[rubydist]

I hate to be called an old guy, but it does fit...

iirc, the times I had this type of symptom were due to:
cam timing off
bad cam sensor or dis
bad injectors

I would double check the cam timing is correct - even one tooth off is a big deal. If that doesn't help, then I would swap on a known good dis (making sure to have enough heat sink grease as SHOdded suggests above) and/or run without the cam sensor plugged in for a while to see if one of those helps.

 

[Jon Klein]

Hey guys thanks for the info... ruby I was using OG as "original ganster" not old guy... either way only the most respect implied. Ive swapped injector sets along with rails and regulator to no avail... i will try cam sensor and DIS. I have spares.

SHOdded... just a tip the "grease" you mentioned on the back of the DIS is NOT GREASE lol. Its very important heat transfer compound... usually white and somewhat dried out from years of heat. But it is super important in preventing the DIS from overheating. It allows the intake crossover to act as a heat sink. Dielecteic grease would act as an insulator and prevent this all so important process because prior to common belief dielectric does NOT conduct electricity and acts more as a heat insulator than a transfer inducer. Always try to reapply fresh heat transfer compound when installing a new or reused DIS. Thanks so much for the posts guys... gonna swap sensor and DIS tonight and report back tomorrow. Also they are motorcraft plugs and wires... two weeks old. And the egr and dpfe are removed... there are more details in the original post. I know its long winded but its all there. Thanks guys. Youre all the best.

 

[rubydist]

Also double check that the plug wire routing is correct, as several of the published diagrams have the wiring wrong.

 

[itwonder]

Since you've ruled out many logical things, that leaves only out of the box things to check. I like rubydist's thought of the timing belt being off a tooth or so, or the cam timing being otherwise off. You could have an exhaust system restriction. You could have a strange intake restriction, like the air filter or hose collapsing at high RPM.

There's an interesting article by a ham that challenges some of the conventional thinking concerning dielectric grease and heat sink compounds. The most important lesson: a thick coat is not better; use a very thin coat for best results.
https://www.w8ji.com/dielectric_grease_vs_conductive_grease.htm

 

[SHOdded]

Interesting what people interpret the term "grease" to mean LOL. It is used today as a generic term, much like "xerox" became a generic term to mean "copy". Certainly did not mean to mislead.

 

[Jon Klein]

SHOdded no worries didnt mean any disrespect of any kind. I really appreciate any and all input from everyone. I was just clarifying for those who might not know. I sure didnt until much later into my mechanical career.

Ruby... wires routed correctly. I have my own diagram that uses the correct routing. (5 and 6 being the two out of sequence) but yes i am aware of the diagram errors and have double checked my work just to honor your wisdom... sometimes it is the simple things that get us but not today lol.

Itwonder... i think youre absolutely right. Whatever it is is definitely "out of the box". Now i was searching this forum and in the "performance mod engine driveline" section there is a guy who swapped a 91 (listed as 89 in the title but it isnt if you read the post) with a 99 v8 motor and used the stock MTX trans and he is having the same issues almost to a T. Since the transmission sensors and mechanical operations are almost identical between the ATX (ax4s) and v8 ATX (ax4n) except for some valvebody changes and the like... this would lead me to believe that whatever this is its transmission (or lack of) related. Especially since it happens right around where the fuel cut would come in if the car was in 4th gear (atx) going 144mph. Approx. 5200-5400rpm.

 

[Jon Klein]

Itwonder... car has SHOshop catless y pipe with the rod shifter short resonator mid pipe (new) and factory mufflers with good flow no restrictions in them. Each side is even flow. Also swapped tps and checked wiring, cleaned MAF and swapped, swapped DIS, swapped coil pack... swapped cam sensor and did all cam seals. The car has an ATX 3.2l block and heads but is dressed with 3.0l manual timing belt setup and 3.0l accessories. Also, all parts used during the swap were from an identical year (1994) MTX car. I have double checked the timing and use the 3.0l belt marks when doing this due to the 3.0l tensioner and idlers setup as opposed to the self tensioning ATX setup. The crank sensor has been replaced in the past and never made any difference in this issue. Tach is working and accurate. Car starts up like it should... going up to 1400rpm or so briefly and settling right down to 900 like it should. No smoking or oil consumption. Valves in perfect adj. No noises.

 

[Jon Klein]

Going to attempt to post a video and codes tonight. Ive never posted a video to the forum in the 17yrs ive been a member... but it cant be too hard i would assume.

 

[rubydist]

post the video on youtube and then put the link in your post.

 

[BaySHO Performance]

I've had several cases of cars bogging down under hard acceleration but working fine under gentle acceleration. Causes I've had are a vacuum leak (even from something as simple as leaving the air hose clamp at the TB loose), bad plug or wire, or dirty MAF. But all of my cases have been between 2-4K, not higher.