Exhaust Manifold/Header Replacement - Page 6

**Uniblurb** · 06-10-2012, 07:36 AM

Thanks for the input guys and don't know about the IAC coralman. I took it off and cleaned it not too long ago but never moved the pintel. Don't know if it would all the sudden go out of whack and fail from engine heat. And even though it was hot yesterday, I was doing 65 mph on the freeway, just installed a new rad/thermostat, and engine temp was running about 205 so really shouldn't be all that hot.

Almost feel like installing a semi-permanent pressure gauge on my intake to see if I'm still having a vacuum leak when the engine's loping. Not sure if this would tell me if there's a problem with the intake/manifold gasket leaking though? I really don't remember this engine loping problem until I installed a new manifold but may just be a coincidence. So is the best trick to shoot carb spray on the gasket area to see if the engine picks up rpm for finding a leak? Not sure if this is the best idea with ice cold carb spray on a super hot manifold? I'm not worried about fire but about cracking something.

Guess something that always sticks in my mind is the TSB which came out 16 years ago on these 96 4.0 ZJ fuel pump assemblies possibly failing. I've noticed new ones, like Bosch, say their pumps won't fail like the OEM fuel pumps from heat. But with a full tank of gas, and doing 65 mph, you wouldn't think my fuel pump, or the fuel in the tank itself, would be all that hot even with 88 degrees out.

But the fuel is leaning out according to my scanner, unusual readings of "0.00" for ST/LT fuel use once in a while, and seems like after making left hand turns the engine doesn't have any pickup.

And there again I can look at my newest reman PCM, where I put zip ties on the connectors and maybe shouldn't have with a newly soldered circuit board? The list goes on......

**coralman** · 06-10-2012, 08:32 AM

Wasn't talking about the IAC, there is a sensor that measures intake air temperature if I'm not mistaken. IAT sensor is what I think its called. It figures in the denseness of the incoming air to help adjust fuel ratios. I don't know if it would throw a code if bad but some move its location to play with the fuel mix. Probaly a long shot.

**Uniblurb** · 06-10-2012, 08:55 AM

Sorry I misunderstood you and think I know what sensor you're talking about. It's a separate one at the back/top of the intake with a 2-wire plug connected. I will say when I cleaned the inside of the intake I removed it and sprayed the end/tip with either carb or brake cleaner spray. Hope I didn't damage it in doing so?

**coralman** · 06-10-2012, 11:49 AM

I don't have a clue,lol. I couldn't find a value for it in the fsm either.

hdrocknroll · 06-10-2012, 12:39 PM

Quote:

Originally Posted by Uniblurb

Sorry I misunderstood you and think I know what sensor you're talking about. It's a separate one at the back/top of the intake with a 2-wire plug connected. I will say when I cleaned the inside of the intake I removed it and sprayed the end/tip with either carb or brake cleaner spray. Hope I didn't damage it in doing so?

Don,t know if cleaning it would damage that, but I cleaned my o2 sensor with brake cleaner, and started having problems, replaced o2 sensor problems gone.

**Uniblurb** · 06-10-2012, 02:16 PM

Bright minds must think alike HD. I also cleaned my cat o2 sensor with brake cleaner, ruined it, and had to replace it! LOL.

I did some troubleshooting and may have found the problem. Before even starting the engine today I connected the fuel pressure gauge to the fuel rail, lost no fuel/pressure, and it read 18psi. Also connected my scanner once I turned the key on. Had code PO171 (Bank 1 system too lean) which must have been saved from yesterday when it was loping. Erased the code and as soon as I started the engine the fuel pressure read 50psi, which is real good.

Let it sit for 10 minutes in the hot sun while idling, hood down, AC on, and fuel gauge still connected. Had the gauge itself clear over between the air box and fender. Drove it down the road 5 miles and let it sit in the hot sun for another 15 min idling. Coolant temp was clear up to 214 degrees and IAT at 196. ST FTRM1 readings went from -28.1, -3.1, -2.3, -0.08, 0.00, but the engine continued to run smooth with no loping.

Drove it home, let it idle for 10 more min trying to get it to lope, and it never did. Popped the hood, grabbed the the fuel gauge by the hose and about burnt the heck out of my hand. Gauge read 58psi and fuel had to be scalding hot/expanding. Let it continue to idle with the hood up and watched the fuel pressure slowly drop to 24psi. I even felt the fuel filter by the tank, along with the metal fuel line, and both were barely warm.

Turned it off, let it sit for 10 minutes, and the fuel pressure dropped to 20psi. It was down to 18psi an hour later. When I released the pressure out of the gauge it came out like foam so must have still been super hot. Granted I may have an injector leak but the fuel pressure sure shouldn't drop from 58/50psi to 24psi with it running. Believe I need to install a new fuel pump assembly unless there's something else, like the PCM, causing the pressure to be reduced? Sure am glad I have 3/4 tank of gas! LOL.

BTW, ran an o2 scanner test 10 min after driving and they were both between .14-.80 so would assume they're still good.

Madpipr · 06-10-2012, 07:22 PM

If SFTRM1 is lower than -10% it typically means a vacuum leak or O2 getting into the system before the downstream O2. I don't know that I've ever seen one at -28.5 though. What is your LFTRM1 at? If that is negative (around the same -28.5) it has learned negative trims from whatever is causing it.

**Uniblurb** · 06-10-2012, 10:12 PM

Quote:

Originally Posted by Madpipr

If SFTRM1 is lower than -10% it typically means a vacuum leak or O2 getting into the system before the downstream O2. I don't know that I've ever seen one at -28.5 though. What is your LFTRM1 at? If that is negative (around the same -28.5) it has learned negative trims from whatever is causing it.

Thanks for the input. The LT FTRM1 started out even worse at -32.0 and slowly followed the readings of the STRM1. Something I've never been able to figure out is both the STRM1 and LTRM1 will both eventually read 0.0. Did it with the last reman PCM and with the newest reman one. If fact when the I saw the STRM1 read 0.0 today I looked at the fuel pressure gauge connected to the rail and it was still reading 48psi.

I also sprayed carb cleaner all around the intake gasket and vacuum lines today and no change at all in engine rpm's. The only thing I can think of in making the fuel lean-out so much is low pressure from the fuel pump. I'm getting ready to order a whole new fuel pump assembly so if someone has some other troubleshooting tips I'd really appreciate some advice. Thanks.

Madpipr · 06-11-2012, 04:37 AM

Take it to a shop and get the system "smoked". You'll find a vacuum leak pretty easily. Though, from the sound of it, it may be the intake/exhaust gasket. Once it warms up the metal expands very slightly and seals your leak. May have to drop it off to a shop one night and let them smoke it first thing in the morning.

**Uniblurb** · 06-11-2012, 07:38 AM

So are you saying one of the throttle body/intake sensors is causing the low fuel pressure readings (24psi), because of an intake leak, rather than the fuel pump itself? Know what you mean about metal expanding and my cracked header used to seal itself up when hot.

But when my fuel leans out the worst is when the engine is hot and it starts loping. So it doesn't seem like any intake leaks are being sealed when hot but that's when they may be the worse if there are any. It loped when I had a brake booster leak but I sealed the rubber grommet in the front housing, where the vacuum line enters, which fixed the problem.

Madpipr · 06-11-2012, 09:00 AM

Where is your STFTRM1 when it starts acting up? I'm not sure what kind of scan tool you have, but if you have one that allows you to reset memory, do it. It will run rough for a few minutes until it relearned itself, but then you can start fresh and see where your adaptives and all are.

**Uniblurb** · 06-11-2012, 10:36 AM

The STFTRM1 can be anywhere, usually in somewhat of a normal range, when it suddenly starts acting up/loping. As mentioned before it always seems to do this when the engine is hot, leans out to -28.1, so it appears to be heat related.

My Actron CP9575 scanner doesn't have the capability of resetting the PCM memory but it will clear error codes. I often disconnect the neg terminal battery cable which should clear the memory on the reman PCM. And it must relearn real quick since never seems to run rough even after start-up in doing this. I can feel very slight misses and wouldn't doubt it's my original injectors.

Madpipr · 06-11-2012, 10:53 AM

http://www.obd-codes.com/faq/fuel-trims.php

Check that out.

**Uniblurb** · 06-11-2012, 12:20 PM

Some real good info to know, thanks. I had considered changing out the front/downstream o2 sensor a couple weeks ago and the one in the cat is new. Guess I need to search for vacuum leaks too. I'd rather try this myself before taking it to a shop and have the intake "smoked". While carb cleaner is supposed to work, in the engine picking up rpms, I really wonder about this? I tried propane too and didn't see any engine rpm changes.

It is evident my fuel pressure is bleeding off with the fuel pump being shut off. Guess there's no way to tell if it's leaking through the the fuel pump/assembly check valve or the injectors?

Madpipr · 06-11-2012, 05:00 PM

Gum cutter/carb cleaner is one way to check for vacuum leaks, but after seeing a smoke machine in action I wouldn't recommend anything else. Every lean code that comes through our shop gets smoked and it has found leaks that I never found before.

There are special gauges to check leak down on fuel pressure, but not cost efficient to use once or twice.

I'm gonna say its a vacuum or intake/exhaust manifold gasket leak.