DOHC problems

[Lyle's GTP]

Hi, My dohc has a multitude of issues. First my idle is not very good, it's not rough I fixed that it was the timing, but it does surge up and down some times usually when hot. Also not much power, I mean I can't even turn them over (spin the tires). Also when I drive sometimes I get some hesitation when I accelerate, some times it kind of surges when I give it gas.

What I have done to the car: Fuel filter, upper intake gasket/EGR gasket, AIC motor/valve, TPS, Magnecor wires, bosch 2 plus plugs, new 170 amp alt., New optima yellow top, new starter, water pump, used A/C compressor, timing belt, serpentine belt/tensioner, smaller alt. pulley, trans flush/filter change, coolant flush/coolant change. I think that is it. No wait I did the coil packs too and cleaned out my TB/plennum. I think thats it. Help...........Please

Lyle

[brian89gp]

What year is the car?

The Bosch plugs might be the cause, pick up some stock R42LTSM (i think that is stock) AC delco plugs, or NGK TR-5's. The DIS ignition tends to eat up all Bosch plugs.

Did you replace the lower intake gaskets?]

The timing may also be out of whack just a little.

[Lyle's GTP]

It's a 94' GTP. I have a MSD DIS-4 to put in and NGK TR5-IX iridium plugs to put in as well, I also have the lower intake gaskets. I'm also going to change all my vacuum lines as well to silicone. I don't think it's the plugs I've tried some AC rapid fires and now these, But the plugs never lookes bad.

[brian89gp]

Did it do it with the rapid fires in there?

Slight hesitation when stabbing the gas I think is normal with the MAF cars.

[Lyle's GTP]

It did. But it's not only when punching it. It sort of surges even when normal driving. There is a hesitation when driving and you punch it. But I think its just the down shift that take s acouple seconds.

[grandprix34]

take off the ICM and have it tested. I had that wierd condition and it was a coil for me, but since you replaced those, then check the ICM

[Lyle's GTP]

Thanks, I will do that when I install my MSD. Has any body used iridium plugs before? Where can I relocate my washer fluid container to, does any body know and where can I get a suitable replacement?

Lyle

[montessgtp]

I have the iridium NGK TR5IX...any if u want my honesty opinion...dont waste your money its a spark plug...AC delco #8 or #12 will do the same exact job. Also im using a washer tank from a 89 Turbo Grand Prix..n moved the small fues box over bout 6 inches..I have yellow top Optima battery. Also where did u get your 170 amp alternator n how much did u pay I have iceburg cs130 and i still have low charging at idle..

[Lyle's GTP]

My 170 amp alternator was $350.00 CDN and was custom built at Cooper Bros Auto Electric here in Edmonton, Ab. Canada. Low charging is something that we have to live with. It's because of the small case GM alternator, when built up to do high output you lose or gain nothing at idle. Here read this reply I did a couple weeks ago.

Hey, it's your lucky day, well sort of. Your alternator probably puts out probably 120 amps max and about 60-70 amps at idle. I have a 94' grand prix gtp and I did the high output alternator thing. I had one custom built here in Edmonton for about $350 CDN it puts out 170 amps which is really good. But here's the deal, do to the cramped mounting conditions you can't physically put a larger case alternator in there, "which would be ideal" like something out of a semi or some other industrial equipment. So you have to gut your small case and put in new parts, New windings, stators, rectifiers, etc. Which is all good except do to the new heavy windings "which is the key part" the output at idle (600-700 rpm) is severly affected. By this I mean the voltage is lowered to 11.5-12.5 and the amperage drops to about 35 amps (at best). However at 1200-1500rpm all is good you get all the amperage you need and 14.5+ volts. But your nice power accesories like the high voltage at idle, power windows and heater fan are badly affected. Same thing for the audio system, if you are crusin' your favorite strip checkin' the hunnies blazin' the tunez, you are not always up there in revs so your high output alternator is worse than your stock one, now it's a toss up. But if you are interested, check out some auto electric places they do this type of work or I've seen them new on ebay as well, for good prices. Sorry man but it's just this 3.4l dohc, any other car you could drop a nice big beast in there. Like my buddy, we found a pro shop crazy enough install a 160amp AC Delco 21SI semi alternator in his 4 cylinder mazda MX-3. It worked awesome, except we had a 2000 watt system in there and if you were at a stop light and you hit a nasty bass note, the load of the alternator would stall his car. But if you have any specific questions about any part of your vehical electrical system or you sound system, caps, batteries wire size that sort of thing, just email me.

Hope that helps.

By the way, I spoke with a guy who build these things and he said that it's possible to build one to put out as much as stock at idle or possibly better, but not much. But it puts out tons at higher RPM. I don't really beleive this though. At least not with this case anyway. I'm not framiliar with your case though.

Lyle

[emileriddle]

Misfire, plugs 2,4,6 w/carbon 1,3,5 fine

Automobile is 1997 Mazda Millenia with 2.5l V6 24 DOHC (not Super Charged)

Summary:

1) Was getting oxygen senor codes(P1170 and P1173)-replaced all 4 sensors

2) Noticed oil around plug wires-changed valve cover gaskets, plugs and wires

3) Started getting multiple cylinder misfire code (P300)-replaced rotor and cap, ran 2 bottled of injector cleaner through and changed fuel filter

4) Continued getting P300-pulled plugs and noticed front plugs (cylinders 2,4,6) were fouled with carbon and rear plugs (1,3,5) were fine. Figured plugs got fouled during oxygen sensor problems. Replaced all plugs.

5) 25 miles later pulled plugs and noted front 3 plug carboning up again, rear plugs are fine.

Am I having an injector problem, fuel regulation problem. How can I diagnose? I tried listening to injectors with stethoscope as recommended on the web. Can not tell difference between different injector sounds. Cannot get to fuel injectors as they are under fuel rail otherwise would check their resistance with an ohm meter.

Car runs poorly once warm, at highway speeds with low rpm (barely pushing on gas pedal) car stutters. At stop lights car nearly stalls. During cold idle car runs fine.

Detailed Story for those interested:

About 3 months ago car began throwing Check Engine Light. Code was P1170. Since I didn't know what the code was I pulled up the plug wires and found oil around them indicating bad valve cover gasket (which is a known problem on Millenias with 50,000 miles. I later found that the P1170 code was a bad upstream Oxygen Sensor. Of note, my car has 3 upstream Oxygen Sensors.

Took it to a dealer who replaced the valve cover gaskets and felt that changing plugs and wires was the answer for the Oxygen Sensor Code despite the fact I was not getting any misfire codes. I tended to agree with them at the time since it made sense to me that oil around the plug wires could be causing problems.

After getting the car back from the dealer the Check Engine Light came back on. Another P1170. Since Oxygen Sensors are not covered by my extended warranty and the dealer wanted $315 each for them I changed all 3 upstream sensors one at a time until the P1170 Code stopped coming up.

The car seemed to be running well for awhile (approximately 200 miles) then I started getting a multiple cylinder misfire code (P300) combined with P1170 and P1173 (which is downstream O2 Sensor Code). I figured that the last O2 sensor behind the converter needed to be changed So I changed it and cleared the codes.

During this whole oxygen sensor fiasco, the car was running poorly as if it was misfiring. Which could be explained by bad oxygen sensors triggering the engine to richen up. I did notice poor engine performance once the engine was warm. At cold idle the car ran fine at warm idle (at stop lights) the RPMs would drop from 800 to ~200 rpm and the engine would almost stall. On the highway during lower RPM driving (my foot barely on the gas pedal) the car would stutter as if misfiring. I ran through two bottles of injector cleaner and did change the fuel filter.

The car continued with check engine lights and poor performance, but now p300, with an occasional p1173. I figured that I was now getting regular cylinder misfires resulting in the Oxygen Sensor codes. The only part of the ignition system that had not really been addressed thus far was the Cap and Rotor.

I changed the Cap, which did appear bad with corrosion build up on all the contacts. The rotor appeared fine, but was also changed. I thought that I had found the magic bullet, car immediately began running better for about 24 hours. Then that damn p300 started in again.

I decided to pull the plugs and put some dielectric grease on them and the boot, since this was the magic bullet on one of my other cars. While pulling the plugs I noticed something interesting. The plugs in the front three cylinders (2, 4, 6) where all carboned up and the plugs in the rear three cylinders (1, 3, 5) where fine. I figured that maybe during the bad Oxygen Sensors days that the car was running rich on the front 3 cylinders. The plugs were pretty bad so I decided to change all 6 again. I have since put about 25 miles on the car (no check engine lights) and pulled the plugs. The front 3 plugs are starting to carbon up again. The rear 3 plugs look like brand new.

I am now at a loss. I think that I have a fuel injector problem on the front 3 cylinders or some type of fuel regulation problem. The car appears to be multiport fuel injected with the fuel line running to a regulator valve then to a fuel rail that supplies the front the cylinders and their injectors. A U-Shaped hose connects the front fuel rail to the rear fuel rail.

[SappySE107]

what? this is over 2 years old. I dont even know what a mazda 2.5 has to do with 60V6s.

[HayesPerformance]

Lyle......... You should get me to look at your GP. We're in the West end by West Ed Mall.


I can even scan it..........

Regards,
Dave

[Dohc Holiday]

Hi, My dohc has a multitude of issues. First my idle is not very good, it's not rough I fixed that it was the timing, but it does surge up and down some times usually when hot. Also not much power, I mean I can't even turn them over (spin the tires). Also when I drive sometimes I get some hesitation when I accelerate, some times it kind of surges when I give it gas.

What I have done to the car: Fuel filter, upper intake gasket/EGR gasket, AIC motor/valve, TPS, Magnecor wires, bosch 2 plus plugs, new 170 amp alt., New optima yellow top, new starter, water pump, used A/C compressor, timing belt, serpentine belt/tensioner, smaller alt. pulley, trans flush/filter change, coolant flush/coolant change. I think that is it. No wait I did the coil packs too and cleaned out my TB/plennum. I think thats it. Help...........Please

Lyle

the first thing you should do when you get any used vehicle, is take it to a competent garage and have the entire computer control system scanned- all the sensors and computer system checked- what I have found is, there are usually a few worn sensors that need changing- most often the oxygen sensor in the exhaust stream, which senses the rich/lean nature of the fuel mixture, and the TPS (throttle position) sensor, which senses throttle angle- also the coolant temp sensor, which senses when coolant reaches operating temp, and puts the vehicle from open loop into closed loop operation. Occasionally there will also be a bad MAP or MAF sensor as well. On a few GM cars I have noticed bad knock sensors as well, which will retard the timing when they should not be- I put a new coolant temp and knock sensor on a 4-cyl DOHC Saturn engine, and it really woke it up.

if all your sensors are ok, then get a fuel pressure/volume test done, and an exhaust backpressure test. When I had that done on my DOHC 3.4, the mechanic found that the converter was slightly plugged (a few pounds of backpressure found), and that fuel volume/pressure was down. He changed the fuel filter and volume came up into specs, but pressure was marginal (1 psi less and he would have changed fuel pump). The way they check exhaust backpressure is, they remove the O2 sensor and put a pressure probe in the exhaust and run the car. My car runs good but basically needs a fuel pump too, which I bought and have to put in.

if all these things are ok, then go to the basics- run a can of cleaner through your fuel tank to clean injectors, OR do what I did, my mechanic attached a cleaning machine to my injector rail, that runs the engine and feeds it from a tank of special cleaner for a certain amount of time (gas tank line disconnected, this machine has it's own fuel feed)

don't mess around, get a set of spark plug wires and plugs and put them in- I run the Bosch lifetime plugs with 4 electrodes, they are pricey $5 each back when I bought them 5 years ago- I just replaced them and they were $7 each, but there was nothing wrong with the old ones- they had 55,000 miles on them and can still be used, so those plugs are a good deal- BTW these are the same type of plugs that piston engine fighter planes and bombers used during WWII and Korean war, so don't believe what you hear that the 4-electrode plugs are no good- they really work- I ran that car for 5 years and never cleaned the plugs

if, after all this, you still have a problem, you may be looking at an internal engine problem- do a cranking compression test and a leakdown test on the engine- it will tell you the condition of the rings and valves/seats- if you have under 125 psi cc, or over 5% leakdown, you basically don't have an engine, and it needs to come out and be rebuilt

none of my post here is in any kind of specific order, you may want to do the cranking/leakdown tests first, etc. Use your own common sense- but this is the procedure I use, and it will find 99.9% of any problems you have. Once in a while there is a weird problem, like a bare wire touching somewhere that is creating a short and f-ing up the computer control. There was a car here once that the driver was some lady that wore high heels, her heel wore through the rug and into a wire harness, wore the wire bare and created a short. There also was another car that when assembled, a bolt for a rear seat went through a wiring harness and created a short. But those kinds of situations are quite rare.

to recap, not in any specific order:

complete sensor/computer check

fuel pressure/volume and exhaust backpressure check

coils/wires/plugs/crank sensor/cam sensor (make sure its getting good, reliable spark)

cranking compression/leakdown check


the most common problems I've found in the past few decades of driving these cars is, the tests usually reveal bad fuel pump, fuel pump relay, plugged converter, bad O2-TPS-MAP-coolant temp sensors, plugs/wires- we have also changed a few computers and proms but not many

almost none of the tests reveal any mechanical wear historically- we did have one DOHC 4-cyl with burned exhaust valves, due to a plugged converter- but most driveability problems are not internal engine problems- unless you are getting a lot of blue or white smoke from exhaust, or pressure blowing into the radiator

hope this helps

[SappySE107]

Bosch plus 4s are horrible with the gm igntion system. I don't care if its WW2 technology. Many people have had issues using them on their 60V6. I tried a set of bosch plugs and they didn't last 10k miles (electrode was almost gone by then).

btw, this thread is from 04 so hopefully lyle doesn't need the help anymore.