QuestionQUESTION: Howard,
First, thanks again for volunteering your time here! I was able to get those stuck lower ball joints out the other night by loosening the upper ball joints from the upper control arms which allowed me to swing the spindle to one side enough to get a good hit on the pin with a sledge hammer. Now that it is running well, registered, front suspension repaired, etc, I drove it quite a bit last night and it developed a small exhaust leak at the second cat converter. No biggie, I know my local exhaust shop can patch it up, but then this evening, after driving all around town at speeds from 30-70 mph, I stopped for a visit of maybe 30 mins and when I left, I experienced a severe lack of power and some mild back fires, but at the exhaust now, not at intake. I pulled over and reached under the car with my lug wrench and tapped the cat converter at which time the front pipe simply fell away from the cat - total disintegration. I thought I would get home just fine then, but I still had reduced, although slightly more power, and if I really got in to the accelerator, some mild backfiring. Your ideas?
ANSWER: Hi Michael,
Your symptoms do not pin point the problem so you need now to run a lot of tests of the system.
First is a compression test then fuel pressure test (32 psi running and about 42 psi with the vacuum pipe removed from the regulator.)
Then check the timing. And check intake manifold vacuum at idle and at high RPM held steady. The fact that when the #2 CAT was pulled down the power improved is a indication of a partially stopped up exhaust. If at high RPM the vacuum slowly goes down means you need to pull one of the plugs on the exhaust manifold and test for back pressure. 1.5 to 3 PSI but no more.
Howard
---------- FOLLOW-UP ----------
QUESTION: Howard,
I know you have a lot to keep up with answering these questions, but I just performed ALL of these tests in the previous weeks of getting the car running, and timing was dead on 17 degrees BTDC, fuel pressure indicated a need for a new regulator, which was replaced, and vacuum pressure at exhaust indicated a clogged exhaust, which seemed to be corrected after I reamed out the first cat converter. The car passed emissions 8/14 with 34/220 and .16/1.20 readings which led me to believe there were no more issues with fuel entering exhaust. My biggest confusion came from the fact that after the the front pipe broke free from the second cat roadside, that I had only a minimal increase in power. I have since investigated, now that the car is cool, and found loose bricks at the inlet of the second cat. Is it possible that debris was sucked, via back pressure, in to the "front" section of the exhaust? I expected to have full, although loud power once I saw the pipe break free of the second cat tonight...
I know you say we must test and verify everything, but it would seem that there should be no need to re-test timing, fuel pressure and vacuum pressure readings that were ok prior to today, when the event seems to be centered around the exhaust. Of course, I'll do whatever you suggest. You are the professor, I am only the student!
Thanks,
Michael
AnswerIf you have the timing correct, (17 deg BTDC) the compression test showed good, (125 to 165 PSI) the exhaust back pressure below (3 PSI at steady high RPM)and the fuel pressure at (32 PSI w/vac and 42 w/no vac)
Then the basics are out of the way and now you need to start testing the injection system.
I always start with the items that have the most influence on fuel mixture. Air flow meter and coolant temp sensor. The air temp sensor and the 0-2 sensor have minor influence on mixture. An ignition problem will usually give you a misfire rather than a loss of power so I would concentrate on fuel.
Except one point worries me. You said "clogged exhaust, which seemed to be corrected" etc. Every time I run into the word "Seems" I find it is from a "Symptom Diagnosis" not a "Test Diagnosis".
Did you retest the back pressure after all the repairs?
The coolant temp sensor (front sensor in the coolant rail)should be,
20C.= 2.5K ohms, 40C.= 1.18K ohms, 60C.= .6K ohms, 80C.= .325K ohms.
The airflow meter usually will have a flat spot in driving conditions not a general loss of power. It is a variable resistor on a carbon track and all you need to do is check between pin 7 and 8 with an ohm meter while moving the flap to see if there is any dead spots. The most ware on the carbon is at the point of normal cruise and will not be a problem at other speeds.
The 0-2 sensor produces voltage depending on fuel mixture and after getting up to operating temp (600 deg F.) .5 v is ideal and a leaner voltage = a lean mixture and a richer voltage = a rich mixture. If this were off you would not have passed your emission test.
There is still a possible problem in the injectors themselves. It is a good idea to run injector cleaner through them. Most shops have the equipment to do this or you can just add injection cleaner to your fuel tank but that takes a long time to work and usually requires several tanks of fuel with the additives in to show any results.
When I have a problem that evades me, I found that making changes that change the problem can in some cases lead me to the cause. For example, If I change timing advance and retard and it changes the problem very little then I look at fuel and change mixture and see if that make any difference. Like remove and plug the vacuum supply to the regulator will give you 42 PSI all the time so thus I have made the mixture rich. The 0-2 sensor tries to counter the high pressure but can not over ride that much extra fuel.
Over the years I have only found a few bad ECUs so I consider that last. I was always fortunate enough to have a known good ECU to try as we never had the expensive tester for ECUs.
Don't over look the transmission in that if it stays in a high gear when it should have shifted down can seem like a loss of power so run your test by shifting manually 1,2 & 3 gear. Don't leave any stone unturned.
