putting this here as well in case it is an internal problem.

Car is an 93 mazda rx7 with an 02 F-body pullout from an auto. The ECU has been reflashed with a manual program. wiring has been converted for manual as well.

Ok, here is what's happening. Dropped the car off this morning to get tuned. Get a call that the car wont rev out past 6k. I had it happen to me a couple of times while I was driving it around but figured it was something with the tune. I didn't want to rev it out to much with the raw tune anyway so I stayed below 4500 for the most part.

He said the car drives fine and pulls strong all the way to right at 6000rpm where it falls on its face. Even free reving it it starts to break up a little over 6k. He has loaded 6 different tunes from 6 different cars and the problem stays consistant. The tunes alter the way the car performs a little but do nothing for the 6k issue. He thinks it is something mechanical that is causing it. It makes good vacuum and works fine at anything under 6k. Fuel pressure is rock solid and the TPS and MAf readings are right on. He has turned off everything in the ECU with regards to knock and chassis feedback stuff. He is an LS1 performance shop and said he has never seen anything quite like this. He ran out of time today so he is going to start checking other things tomorrow.

we want to recheck pushrod length and maybe swap the coils. Any suggestions would be great. I trust him but if there is something that is particular for the swap, he will not be on top of that. He works on a lot of corvettes and GTO's. Pretty much lS1 stuff.

My particulars are as follows:

Stock bottom end with ARP rod bolts
CNC'd 243 casting heads with 2.05int and 1.6exh valves milled 20thou
crane double springs with titanium retainers
comp cams 232/236 .595/.600 114lsa cam
flycut pistons
LS4 oil pump
ls2 timing chain
GM high rev lifters
comp cams 7.450 pushrods
Jesel shaft mount 1.7 rockers
LS6 intake
cometic .40 gaskets
fuel system holding 58psi
38# injectors
slp 85mm maf
jtr long tubes

hope to figure this out asap and hope its not going to be internal.

Mike

 

I'm going to guess valvetrain. Who setup the rockers?

 

Make sure the throttle is opening all the way with a volt meter.

 

yours truley. I am using Jesel J2k's with 1.7 rockers. These are older units and do not have the lash adjuster. we mounted the shaft to the heads as per instructions by torquing the shaft bolts to 22ftlb. We then used an adjustable length pushrod to check for length with everything assembled. The valves and springs were already installed on the heads and had just come back from the head builder for freshening. I bought them like this used from a person who was a customer of my tuner who knows the heads well. After getting them back, the owner decided to go with a big block and put them up for sale along with the Jesels. I snatched them up and put them on my Ls1.

Since my cam was different and so was my gasket, I wanted to check to make sure I got the correct pushrod length for preload. I am using the GM high rev drop in lifters which require stock preload. We turned the crank to its base circle and dropped in the adj. pushrod. We then bolted down the rockers and unscrewed the pushrod until the lash was gone. We took the pushrod out and measured it and found the closest length to get the 50thou preload we were shoouting for. The only thing I am unsure about was that the lifters were brand new when installed and had never been pumped up. They should still be fully extended though shouldn't they? If not then maybe we oversized the pushrods.

Mike

 

I will double check this but I think he said it was. Putting this on the list as well.


Mike

 

Ok, here is the theory I am working on. This theory assumes that it is mechanical and not electrical. Both possibilities are still open but my tuner thinks its mechanical so I am working on that at the present.

Since it seems that I did eveything correct when measuring the pushrod length, the only possibilities for valve float would be either lifters over pumping up or bad valve springs. He says the car idles fine and drives fine all the way up to 6k. After 6k it runs like **** for a bit till it recovers. The heads were just gone through so I am putting my attention to the lifters.

I am running the high volume LS4 oil pump. I am seeing over 100psi on my Defi gauge. Is it possible that too much oil pressure is taking all the preload out of the lifter and driving the plunger all the way to the top at high Rpm. This might be floating the valves as they can no longer shut. After letting off, the lifters remain pumped up for a bit and the car now runs like **** until they bleed back down and everything returns to normal. Has anyone else here run this pump and/or experienced this type of problem.

On the dyno we are getting 401hp at 6050 rpm and then it plummits to 250 something by 6150. Fuel pressure is rock solid at 58 psi. As stated after the pull it runs like crap for a bit till it recovers. Then runs fine unless we rev it past 6k again.


Mike

 

On the electrical side, I have a 85mm MAF. It has the resistor on it so it is probably an SLP. I asked if that was the problem but he said the MAF is working fine and all the freq. are in range. I am mis quoting but the point is that he looked at that and saw nothing wrong. He was originally going to cut it out and redo the tables but after logging it on the Dyno, he said no need.

Could there be another problem here that we are missing.

Mike

 

my guy called and said that he installed stock pushrods and now the car revs all the way out to 7 grand and idles much better. He also said it has way more valve train noise. I assume this is due to loosing preload. It seems my car doesn't like either end of the spectrum. What gives? Stock pushrods are like 7.385-7.395 correct? I had 7.450 installed. Max change is .065. This is well in the realm of factory preload.

Also, oil pressure hit 140 when we hit the peak hold button on the gauge. This is way too much. How can this affect the lifters.

Mike

 

turned out to be the pump. I bought a stock z06 pump and pressures are 35-40 idle and no more than 75 at WOT. I still have valve float though. I think the springs need to be replaced. They are crane duals(144832's I believe) and were used with the heads. I am not sure they are up to the task. I am going to have them replaced.

My cam is a comp xer grind 232/236 .595/.601 114lsa. The springs are crane duals according to the previous owner. He had a much more aggresive cam than this so I figured they would be fine. Maybe they are just worn down or not shimed enough. Do you guys think that these springs are under rated for this cam. I am also running Jesel sportsman series shaft mount rockers. They are stock 1.7 ratio. I also have hardened pushrods which give me .060 preload on the caddy lifters. I am considering the new patriot extremes or the crane 144833's. Since I already have the locks and such, I can just buy the srings.


Also, of interest is that the part # on the LS4 pump I was sold does not match either of the part #'s listed in the SDPC thread. As a matter of fact, we can't find the part # on any GM website. I plan on calling Fred Beans on Monday. This pump might not even be for my this engine.

Mike

 

Although I have no real world experience, I have read on here (take with a grain of salt) of people having issues with the LS4 pump. And they guy who has the problems has 140psi and feels the lifters are maxed out (pumped up due to oil pressure). But interesting the stock PR's allow you to get to 7K so preload must be off. I would think the springs you have are fine but as you mentioned, check for for spring height etc.

 

That is me, I posted in different threads trying to get help. the shorter pushrods gave almost 0 preload. They were noisy has all hell. Even though it rev'd to 7k, the hp curve fell and then climed again. It was very abnormal. Since the oil pressure is now correct. The only place to move onto is the valvetrain. Multiple threads say to use .060 preload on the caddy lifters. This is what I have. ???

 

maybe it is a BBC oil pump...LOL J/K

Sounds like you are well on your way to fixing the problem. I was going to suggest valvetrain...you are already there. I would not have used the used springs if I were you and would have gone with the LS6 pump to begin with but that is just me. I did buy the caddy lifters...we will see how that works out. I don't know anything about those shaftmount rockers though.

Good Luck
Jon

 

Sorry, I didn't realize it was you. Did he put the stock PR's in AFTER you replaced the pump? If so, you don't know if it was the pump or PR's that helped. BUT, if you have a dip then obviously the sprigns need looked at.