95 Rodeo fuel pressure

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95 Rodeo fuel pressure

Postby HHD » Sat Oct 15, 2016 8:29 pm

My wife drives a 1995 Rodeo 3.2 SOHC. It has been a really good vehicle with few problems. Lately, it has begun to idle rough, sometimes lose power and once in a while make a little backfire noise. The rig has 240,000 miles and always starts fine, but the idle becomes rough especially after putting it in gear. I have changed the timing belt, MAP sensor, plugs and wires and cleaned the throttle body and EGR valve. It is somewhat smoother, but down on power.
I put a fuel pressure gauge on it this afternoon and got consistent readings, but can't find what the normal should be. With the key on and the engine not running the gauge showed 55 PSI, when I start the engine the reading falls to a steady 35PSI. I have looked at numerous sources and can not find if this is acceptable. Anyone have the facts for this engine? I usually work on older vehicles than this and the fuel injection stuff is out of my line.
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Re: 95 Rodeo fuel pressure

Postby Buster28 » Mon Oct 17, 2016 5:51 am

With the engine fully warmed, the fuel pressure on my properly running 02 Rodeo 3.2L dohc engine is 38 PSI Key On with engine not running. When the engine is running at idle at approximately 800 RPM the pressure is 34.5 PSI. My other vehicles have similar numbers. I expect your engine would be similar.
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Re: 95 Rodeo fuel pressure

Postby HHD » Mon Oct 17, 2016 10:42 am

So I guess the pump is good. This thing is driving me crazy. I have tried most of the things I have seen suggested for very little gain. Sometimes the engine seems smooth when started and revs good and then the miss starts again with power loss and roughness. I just did an ohm test on the injectors and they were all at 12 ohms. I have been searching for cracked hoses and bad wires, but no luck. There are no codes.
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Re: 95 Rodeo fuel pressure

Postby Buster28 » Mon Oct 17, 2016 11:30 am

Recommend you re-check the injector resistance when the engine is hot.
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Re: 95 Rodeo fuel pressure

Postby HHD » Mon Oct 17, 2016 1:54 pm

I had to pull the plenum to reach all of the injectors so I can't check them hot.
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Re: 95 Rodeo fuel pressure

Postby Buster28 » Mon Oct 17, 2016 2:52 pm

Is there an electrical connector(s) between the injector wiring harness and the ECM that you can access?
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Re: 95 Rodeo fuel pressure

Postby HHD » Mon Oct 17, 2016 5:31 pm

I'm not sure. I'm not even sure where the ECM is on this vehicle. I was planning to check it over for bad connections or grounds.
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Re: 95 Rodeo fuel pressure

Postby HHD » Sat Oct 22, 2016 11:03 am

I got the plenum and assorted parts back on the engine and took the Rodeo for a drive. The problem persists. Engine starts quick, but soon you can feel a shake or roughness in the idle. The vehicle sometimes idles fast and the idle will rise and fall a few hundred rpms as the engine warms up. On the road the vehicle sometimes hesitates and then pulls well especially if the transmission downshifts. Level and downhill road is good, but if you encounter much of a hill the vehicle will not pull well. Once in a while as I pull away from a stop I get a slight backfire. All of this is pretty much what I had before all of this effort. The only known bad part was the MAP sensor which I replaced.
Before I replace any more parts, I would like to isolate the problem cylinder(s). How do I do this without damaging anything? Can I pull the wires at the coil one by one without doing any harm? How about checking the injectors when I can't reach half of them?
Oh yes, what are the symptoms of a bad fuel regulator and how do I test it?
Please help. My wife needs her Rodeo back.
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Re: 95 Rodeo fuel pressure

Postby Buster28 » Sat Oct 22, 2016 7:10 pm

HHD wrote:I How about checking the injectors when I can't reach half of them?

The injectors are fired in left bank right bank pairs. If you can get to the injectors in one bank you can also measure the resistance of the paired injector. With the engine Not Running, pull the connector off one injector and measure across the pins on that injector. Measure across the connector pins to measure the paired injector resistance. The pairs are 1&2, 3&4, 5&6.
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Re: 95 Rodeo fuel pressure

Postby HHD » Sat Oct 22, 2016 8:02 pm

This would be different than the reading I got by checking each injector before when I had the plenum off? Do you mean while the engine is cool or warm? Is there a specific number or am I just looking for a difference between the pairs? Each injector checked at 12 ohms when I did them one by one.
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Re: 95 Rodeo fuel pressure

Postby Buster28 » Sat Oct 22, 2016 9:15 pm

This test allows you to measure the injector resistance when the engine is hot. They should still be 12 ohms when hot.
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Re: 95 Rodeo fuel pressure

Postby HHD » Sat Oct 22, 2016 10:49 pm

I'll try that. Thanks.
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Re: 95 Rodeo fuel pressure

Postby HHD » Tue Oct 25, 2016 3:21 pm

I must be missing something in your instructions. I got time to try checking the injectors hot, but realized that I can't even see most of them with the engine assembled. Am I supposed to pull the throttle body and EGR to get access? Will the engine still be warm enough by then?
I wish this engine had a carburetor and distributor. I know how to work on those.
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Re: 95 Rodeo fuel pressure

Postby Buster28 » Wed Oct 26, 2016 8:09 am

If you can't easily access the connectors the only other way is to measure the injector pair resistance at the ECM connector. I can post the connector pin out if you want to try that.
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Re: 95 Rodeo fuel pressure

Postby HHD » Wed Oct 26, 2016 9:44 am

Any information would be useful. I have a repair manual on order, but it won't be here for several more days.
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Re: 95 Rodeo fuel pressure

Postby Buster28 » Wed Oct 26, 2016 11:43 am

The ECM is behind the LH ("driver") kick pad.
The PCM wiring harness connector image is showing the pin side. Remove the connector from the ECM to measure the injector resistance.
Click on image to expand.
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Re: 95 Rodeo fuel pressure

Postby HHD » Fri Oct 28, 2016 6:25 pm

After reading the fuel pressure info in the Chilton's manual, I went ahead and changed the fuel pump and strainer. It took most of two days to do it in the driveway and I got lots of dirt in my all over me, but the good news is that the pump cured most of my issues. There is still a roughness in the idle I don't like, but the Rodeo will now climb hills without seeming to be out of power. I guess 35 pounds at idle was not enough. I still want to get that roughness out.
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Re: 95 Rodeo fuel pressure

Postby HHD » Mon Oct 31, 2016 6:57 pm

I think I can eliminate the injectors. I listened to them with a stethoscope and they all sounded alike. I checked the resistance at the ECM with the engine warmed up and they all checked 11.2 Ohms.
The engine starts well, but the idle at 700 rpm is not smooth. I also noticed that if I raise the idle and try to hold it the tach will range up and down about 200 rpm. My son-in-law says his Dakota was doing the same thing until he changed his oxygen sensor. Could this be my problem? The Rodeo is not throwing a code, but he says his truck didn't either.
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Re: 95 Rodeo fuel pressure

Postby Buster28 » Tue Nov 01, 2016 5:54 am

I don't think you have an O2 sensor problem, do you have a scan tool that can monitor the O2 sensor output?
Btw, what is the fuel pressure with the new pump?
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Re: 95 Rodeo fuel pressure

Postby HHD » Fri Nov 11, 2016 2:22 pm

Okay, since I last posted, I changed the 02 sensor, but no great change. I began searching more on other sites and found a description of testing the fuel regulator. After borrowing the fuel pressure gauge again, I hooked up a vacuum pump to the fuel pressure regulator and, even though it held vacuum, the readings on the fuel pressure gauge were inconsistent while the engine was running. I went ahead and changed the regulator and it seemed to help with the surge that occurred sometimes when pulling away from a stop.
I added SeaFoam to the gas and took the Rodeo on some drives. Yesterday I drove over 100 miles and the Rodeo runs much better, but not right. It still idles rough much of the time and will not pull very well when accelerating. Also, it still does not pull steep hills very well. On flat road or a downhill section everything seems normal. When I pulled onto the 4 lane up a slight hill it took a long time to get up to 70 MPH and the transmission did not shift to 4th until almost 70. On a downgrade the getting to 70 seems normal.
My wife drove the Rodeo this morning for the first time since I began working on it and remarked on how much better it runs. I feel like there is some little factor that will put this thing right, but I don't know what it is. My wife is going to drive it for a few days and give the SeaFoam a chance to do its stuff. Maybe an injector is sticking.
BTW This may not apply to other years, but on this model Rodeo with the 3.2 I would stay away from the universal type 02 sensor where the wires have to be adjusted to fit. The sensor my brother brought me from O'Reilly was well made, but the harness had to be so short that it was a pain to add the splice. I would pay a little more for the one made to fit my application next time.
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Re: 95 Rodeo fuel pressure

Postby HHD » Tue Jan 03, 2017 7:55 pm

My wife has been able to drive the Rodeo, but there were severe problems with lack of power and low fuel consumption. I had decided today to try blocking the vacuum sources and see if it helped. When I removed the air filter housing I found one of the vacuum hoses had come off of the throttle body. The hose was hard so I replaced it with a new one. The engine runs much better, but still has a slight roughness that doesn't seem right. We will drive it for a bit and see if it improves.
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Re: 95 Rodeo fuel pressure

Postby HHD » Sat May 13, 2017 12:10 pm

I changed the injectors a few days ago. The engine runs better and no longer shudders when the pedal is pressed down. Unfortunately, I think the transmission is slipping. I think this was why the Rodeo would not pull hills well, but the problem was masked by the engine trouble.
Just when I think I've got it fixed something else crops up. Now I have to learn about Isuzu automatic transmissions. :(
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Re: 95 Rodeo fuel pressure

Postby Grayfox » Sat May 20, 2017 6:44 pm

as i started reading this post, i was scream to my self put a smoke machine on it and run a direct line to the fuel rail injector cleaning, this sounds exactly like a vacuum leak and injectors that are plugging up. my guess is buying new injectors was much like buying a new pair of blue jeans because the one you have on are dirty. sadly people put far to much trust in the rip off injector cleaners that you put in the gas tank, that hardly ever work
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Re: 95 Rodeo fuel pressure

Postby HHD » Sun May 21, 2017 1:26 pm

I did check the fuel rail while it was off. Some of the injectors looked bad on the ends and one had an o ring that looked like it had been seeping. They served well for almost 250,000 miles so I figured it was time for a change.
Is there a particular place the engine could develop a vacuum leak?
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Re: 95 Rodeo fuel pressure

Postby Grayfox » Sun May 21, 2017 3:03 pm

typically on older cars like these Rodeos.. vacuum hose seem to be the first to go ( dry rot, cracking(i always spray anything rubber with AT 205 reseal available on Amazon, it rejuvenates rubber)), the vacuum switch valve for the egr, and the evap purge, likes to start leaking, which then is the same as having a hose disconnected from the intake. its the little square valves on top the manifold on a older rodeo. the the egr diaphragm and or Pintle shaft( but those pintle shafts even new will sometimes leak a little, you just do not want a huge leaked there) Egr is the one closest to the throttle body, evap purge in the one closest to the charcoal canister. the other common one i have noticed on them is in particularly on the first generation Isuzu motors('93.4 and 5) is the rear cam plugs disintegrate. true this is more of a crankcase vacuum leak as long as ur pvc is good, but i have traced it to be the contributing factor to letting dirt in and helping speed on the clicking of the valve train. you can feel back there with ur hand...if it feels like a empty hole with a shaft in there ... then the plug is gone completely. or you can feel holes in the plug.. the plugs look like old metal freeze plugs for a block only they are plastic and tap in like a normal seal would. and . check where ur throttle body bolts on, and the hose for the fuel pressure regulator comes out of the manifold... right to the right of that on the bottom under a lip in the casting of the manifold is another vacuum port that is just capped with a rubber plug... i have seen dozens of those rubber plugs dry rotted or gone completely.. if you have access to a smoke machine pump the smoke into the dip stick tube and if the valve covers ,rear cam seals or spark plug tube seals are leaking you will know it in about 2 minutes.
hope something in all that was of use to you.
here is a link (you can copy and paste) to a picture of the rear cam plug. i just did a search for my '93. but its the same motor
http://www.partsgeek.com/catalog/1995/i ... _plug.html

the evap purge valve is easy to check with a traditional vacuum pump.. it is a normally closed calve so it should not leak down. unless you energize it.
the Egr valve you have to make sure is not leaking threw the vent port on the back of the valve. i dont remember with out looking at it what the steps to test it are.. i think one port holds vacuum and one pulls air threw the vent and when you energize the valve it switches which one pulls holds the vacuum, i would have to look at it to remember

a heads up. if the evap purge is leaking. start praying because i have not been able to find them new anywhere and finding used one is tuff.. normally i can put a few drops of the AT205 in the bottom and top ports and let it soak in the rubber for a 6-7 hrs and then energize the valve and spray WD-40 to flush it out. i learned the hard way do not let the AT 205 soak in there very long .. LoL is such a small space in there that the rubber of the valve swells up so much the freezes up and wont function at all... so it is better to do a few short soaks that one long one.
.
side note for the AT-205 re seal.. i tried as a test .. i filled a small measuring cup with it, and that dropped a o'ring in it (the condition of the oring, was 3/4 diameter, was somewhat of the worn flat spots they get, mostly crushed flat, but still flexible) after a 24 hrs soak. the had expanded to almost more than half its original thickness and measured just over 7/8 in diameter. but i spray it on anything rubber.. body to frame bushing, cv boots, ball joint boots. i keep it in a sprat bottle and just go over the entire car any time i open the hood. and rubber clearly lasts longer.. ok i will shut up now i have rambled on and this is waay to long of a post

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