1993 Camry 4 cylinder Losing Power Under Load

[ukrkoz]

Fuel pressure. Check fuel pressure. Under load means more fuel is required and you may have clogged fuel filter or weak fuel pump. Even bad connector on pump.

[frafreg]

Thank you for your reply. I noticed the timing was very unstable at idle after warm up. I'm using the TOYOCOM device which enables me to look at live data and it shows the timing moving up and down from about -5 to about -1 while idling. I tried to advance the timing to -10 degrees, rotating the distributor counter clockwise, but I was only able to get it to about -5.3. That was as far as the distributor could move. Although the timing is still wrong, the idle became smooth and the timing got steady. I took the car for a drive and there was no longer any trouble going up a hill with the car under a load.
I need to go back and check the base timing with a timing light and jumper TE1 and E1 in the diagnostic connector per the service manual. I suspect the timing belt may have jumped a notch, but I can't be sure until I hook up the timing light. Any thoughts would be helpful. Thanks again!

[Brian R.]

I doubt it is the timing belt. Bad valve timing would cause you greater problems than what you are seeing. The timing you see when you jump the connector will tell you the story. If your timing is stable and within spec, you are probably in good shape.

If your valve timing were off by one tooth on the timing belt, Changing the the ignition timing by rotating the distributor would not correct it. Check your compression to check if the timing belt is off by a tooth.

[frafreg]

I adjusted the timing to 10 degrees btdc at idle with E1 & TE1 connected. When I removed the jumper, the timing went to 5 degrees btdc instead of 13 to 22 as described in the service manual. The bad idle returned.
I removed the vacuum hose from the fuel pressure regulator, held my finger over the vacuum hose and the idle returned to normal. I think the fuel pressure went up or at least closer to normal. Unfortunately, I was unable to check fuel pressure before or after removing the vacuum hose because I didn’t have the correct adapter to connect to the outlet of the fuel filter. Since the idle got normal and there is no fuel coming out of the fuel pressure regulator, I think the problem must be with the fuel filter or the pump.
I went online and I think I found the correct adapter.
Link to adapter:
https://www.ebay.com/itm/Banjo-Bolt-...mvSB=true#rwid

Any thoughts or suggestions? Thank you.

[Brian R.]

Anywhere from 0 - 10 deg BTDC is correct for your engine. Double check your service manual.

If it were your fuel supply, you would not be able to correct it periodically as you made changes. It would always be bad. Your problem may be with some sensor giving the ECM bad data, like your coolant temperature sensor or your manifold pressure sensor or crankshaft position sensor, etc. Perhaps your distributor is installed with the shaft indexed incorrectly. Remove the distributor and make sure you install it correctly, lined up with the #1 cylinder at TDC on the compression stroke.

[frafreg]

I marked the position of the distributor on the outside, and the position of the rotor to make sure I put it back in the exact same position.
There is no separate crankshaft position sensor. The cam and crank angle signal comes from pickup coils inside the distributor. NE + and NE- is the crank angle and G + and G – is the cam angle. I checked the resistance and the air gap for both coils and they were good.
The only thing that gave me a smooth idle was removing the fuel pressure regulator vacuum hose while plugging the vacuum hose. That didn’t fix the hesitation under a load. Advancing the distributor as far as it would go corrected the hesitation under a load but didn’t correct the rough idle.
The ECT temperature looks correct according to the live data I see from the TOYOCOM.
I’ll go back and check the MAP sensor with a vacuum gauge to make sure the power output drop is correct at different levels of vacuum.
Thanks for your help. I’ll let you know my findings.

[Brian R.]

Did you check the compression? Is your engine operating temperature normal or is it low?

Is the intake manifold vacuum in the normal range at idle? Gasket leak in intake manifold? Bad vacuum hose connection, leaking vacuum system hose?

Since the battery change apparently started the problem (maybe), check the power wire on the battery (positive terminal) which is separate from the high-amp starter connection. If the connections or conductor are questionable, they are potential sources of erratic electrical behavior.

[frafreg]

I haven't checked the compression. The engine operating temperature is normal. I will have to find out what normal intake manifold pressure should be at idle.
I'm told that the problem did happen before the battery change but got worse later on. I have since removed, cleaned and checked the battery terminals.

The vacuum hoses for the fuel pressure regulator and the MAP sensor come from the same port on the intake. There is a "T" fitting with both hoses. Is there anything about that "T" fitting I could be missing?

[Brian R.]

That T-fitting is ok unless it's broken or the hoses are loose.

Intake manifold vacuum should be 60 kPa, 450 mmHg or 17.7 inHg at idle. Make sure that your idle is stable before you make a judgement from this measurement. A bad running engine (like one with a miss) will have strange vacuum because you are opening the throttle to make the engine idle correctly. The throttle has to be closed to make a judgement on vacuum with the idle speed around normal.

Compression pressure in a new engine at operating temperature with plugs removed is 178 psi or more. Older engine should be not less than 142 psi with not more than 14 psi difference between cylinders.

Other specs: page EG-1-140 in manual

The battery terminals are not the issue. They are for high current. The connections and wire that you should test is the relatively small one from the positive battery terminal to the fuse box or near the fuse box. This wire can be corroded badly within the insulation and be a poor or intermittent conductor.

[frafreg]

The “T” fitting looks good. I also checked it for leaks with carb cleaner. Thanks for the intake vacuum numbers at idle. I went to Harbor Freight Tools tonight to buy a vacuum pump kit made by Pittsburgh, to test the MAP sensor. My luck, the one I bought was bad out of the package. I need to go back and get a new one tomorrow. I’ll check the intake manifold vacuum also.
I’ll try to do a voltage drop test on the wire going to the fuse box.

The weird thing is that I pulled the vacuum hose for the fuel pressure regulator, held my finger on the hose then, plugged the hose back in again. The idle got smooth without doing anything else. A minute or two later, the idle got bad again. Maybe I disturbed the vacuum for the MAP sensor since they are both on the same port. I could be wrong. I need to do more tests. It’s surprising that I would have such bad hesitation under a load without getting any error codes. Thanks again for your help and information. It is greatly appreciated!

[Brian R.]

Many times, what I do is hang out at a Toyota dealership service department and ask to talk to a mechanic. I always am able to talk to someone who is knowledgeable and give me some ideas on how to solve a problem. If they are an experienced mechanic, they have seen everything.

[aleekat]

Originally Posted by frafreg

The weird thing is that I pulled the vacuum hose for the fuel pressure regulator, held my finger on the hose then, plugged the hose back in again. The idle got smooth without doing anything else. A minute or two later, the idle got bad again. Maybe I disturbed the vacuum for the MAP sensor since they are both on the same port. I could be wrong. I need to do more tests. It’s surprising that I would have such bad hesitation under a load without getting any error codes. Thanks again for your help and information. It is greatly appreciated!

If you smell gas in that vacuum line or some gas trickles out, then you have a bad fuel pressure regulator. About $65 at rockauto.

[frafreg]

I didn't smell any gas or see any fuel come out of the fuel pressure regulator. I think I have finally narrowed it down now to the area where the problem may be. I hope the results of the MAP sensor test will finally reveal what is wrong. I got a bad vacuum pump tester from Harbor Freight Tools last night and I won't be able to carry out the test until I get a new one. It's is made by Pittsburgh. Maybe I'll opt for the better one made by Mityvac for $12 more. I need something that is reliable especially when troubleshooting something like this with no error codes. Thanks for your help aleekat.

[aleekat]

Originally Posted by frafreg

I didn't smell any gas or see any fuel come out of the fuel pressure regulator. I think I have finally narrowed it down now to the area where the problem may be. I hope the results of the MAP sensor test will finally reveal what is wrong. I got a bad vacuum pump tester from Harbor Freight Tools last night and I won't be able to carry out the test until I get a new one. It's is made by Pittsburgh. Maybe I'll opt for the better one made by Mityvac for $12 more. I need something that is reliable especially when troubleshooting something like this with no error codes. Thanks for your help aleekat.

Not out of the regulator, the vacuum hose.

[frafreg]

I tested the MAP sensor today and although it is slightly out of spec, I don’t think it’s bad. I have 5 volts reference at the connector. According to the service manual the signal voltage should read 3.96 volts with no vacuum. I read 3.63 volts. Below are the rest of my readings.
Engine Warmed Up
Map signal voltage at idle - 1.5 volts
Vacuum Reading – 33 kpa
23.99 kpa to 37.33 kpa (Service manual specification)

MAP Sensor Bench Test
Reference voltage - 5 volts at connector
Specified Signal voltage with no vacuum – 3.96 volts

Volts Drop
No Vacuum 3.63
13.3 kpa - 100 mmHg 2.79 .86
26.7 kpa - 200 mmHg 2.38 1.27
40.0 kpa - 300 mmHg 1.96 1.67
53.3 kpa - 400 mmHg 1.58 2.07
66.7 kpa - 500 mmHg 1.17 2.48

There was no smell of gas coming from the fuel pressure regulator hose. I went back to AutoZone tonight to rent the fuel pressure test kit and they had one in stock. The next test will be for fuel pressure.
What still confuses me is that the car had no trouble under a load after I advanced the timing but still had a rough idle. Does that mean my fuel pressure is ok as well as my compression?
I also checked the wire coming from the battery to the fuse box and it was good. Thank you.